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Hu W, Figueroa‐Balderas R, Chi‐Ham C, Lagarias JC. Regulation of monocot and dicot plant development with constitutively active alleles of phytochrome B. Plant Direct 2020; 4:e00210. [PMID: 32346668 PMCID: PMC7184922 DOI: 10.1002/pld3.210] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 02/03/2020] [Accepted: 02/25/2020] [Indexed: 05/31/2023]
Abstract
The constitutively active missense allele of Arabidopsis phytochrome B, AtPHYBY276H or AtYHB, encodes a polypeptide that adopts a light-insensitive, physiologically active conformation capable of sustaining photomorphogenesis in darkness. Here, we show that the orthologous OsYHB allele of rice phytochrome B (OsPHYBY283H ) also encodes a dominant "constitutively active" photoreceptor through comparative phenotypic analyses of AtYHB and OsYHB transgenic lines of four eudicot species, Arabidopsis thaliana, Nicotiana tabacum (tobacco), Nicotiana sylvestris and Solanum lycopersicum cv. MicroTom (tomato), and of two monocot species, Oryza sativa ssp. japonica and Brachypodium distachyon. Reciprocal transformation experiments show that the gain-of-function constitutive photomorphogenic (cop) phenotypes by YHB expression are stronger in host plants within the same class than across classes. Our studies also reveal additional YHB-dependent traits in adult plants, which include extreme shade tolerance, both early and late flowering behaviors, delayed leaf senescence, reduced tillering, and even viviparous seed germination. However, the strength of these gain-of-function phenotypes depends on the specific combination of YHB allele and species/cultivar transformed. Flowering and tillering of OsYHB- and OsPHYB-expressing lines of rice Nipponbare and Kitaake cultivars were compared, also revealing differences in YHB/PHYB allele versus genotype interaction on the phenotypic behavior of the two rice cultivars. In view of recent evidence that the regulatory activity of AtYHB is not only light insensitive but also temperature insensitive, selective YHB expression is expected to yield improved agronomic performance of both dicot and monocot crop plant species not possible with wild-type PHYB alleles.
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Affiliation(s)
- Wei Hu
- Department of Molecular and Cellular BiologyUniversity of CaliforniaDavisCAUSA
| | - Rosa Figueroa‐Balderas
- Public Intellectual Property Resource for Agriculture (PIPRA)University of CaliforniaDavisCAUSA
- Department of Viticulture and EnologyUniversity of CaliforniaDavisCAUSA
| | - Cecilia Chi‐Ham
- Public Intellectual Property Resource for Agriculture (PIPRA)University of CaliforniaDavisCAUSA
| | - J. Clark Lagarias
- Department of Molecular and Cellular BiologyUniversity of CaliforniaDavisCAUSA
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2
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Oh J, Park E, Song K, Bae G, Choi G. PHYTOCHROME INTERACTING FACTOR8 Inhibits Phytochrome A-Mediated Far-Red Light Responses in Arabidopsis. Plant Cell 2020; 32:186-205. [PMID: 31732705 PMCID: PMC6961613 DOI: 10.1105/tpc.19.00515] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Revised: 10/25/2019] [Accepted: 11/14/2019] [Indexed: 05/04/2023]
Abstract
PHYTOCHROME INTERACTING FACTORs (PIFs) are a group of basic helix-loop-helix (bHLH) transcription factors that repress plant light responses. PIF8 is one of the less-characterized Arabidopsis (Arabidopsis thaliana) PIFs, whose putative orthologs are conserved in other plant species. PIF8 possesses a bHLH motif and an active phytochrome B motif but not an active phytochrome A motif. Consistent with this motif composition, PIF8 binds to G-box elements and interacts with the Pfr form of phyB but only very weakly, if at all, with that of phyA. PIF8 differs, however, from other PIFs in its protein accumulation pattern and functional roles in different light conditions. First, PIF8 inhibits phyA-induced seed germination, suppression of hypocotyl elongation, and randomization of hypocotyl growth orientation in far-red light, but it does not inhibit phyB-induced red light responses. Second, PIF8 protein accumulates more in far-red light than in darkness or red light. This is distinct from the pattern observed with PIF3, which accumulates more in darkness. This PIF8 accumulation pattern requires degradation of PIF8 by CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) in darkness, inhibition of COP1 by phyA in far-red light, and promotion of PIF8 degradation by phyB in red light. Together, our results indicate that PIF8 is a genuine PIF that represses phyA-mediated light responses.
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Affiliation(s)
- Jeonghwa Oh
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
| | - Eunae Park
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
| | - Kijong Song
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
| | - Gabyong Bae
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
| | - Giltsu Choi
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea
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3
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Qiu Y, Pasoreck EK, Reddy AK, Nagatani A, Ma W, Chory J, Chen M. Mechanism of early light signaling by the carboxy-terminal output module of Arabidopsis phytochrome B. Nat Commun 2017. [PMID: 29199270 DOI: 10.1038/s41467-107-02062-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023] Open
Abstract
Plant phytochromes are thought to transduce light signals by mediating the degradation of phytochrome-interacting transcription factors (PIFs) through the N-terminal photosensory module, while the C-terminal module, including a histidine kinase-related domain (HKRD), does not participate in signaling. Here we show that the C-terminal module of Arabidopsis phytochrome B (PHYB) is sufficient to mediate the degradation of PIF3 specifically and to activate photosynthetic genes in the dark. The HKRD is a dimerization domain for PHYB homo and heterodimerization. A D1040V mutation, which disrupts the dimerization of HKRD and the interaction between C-terminal module and PIF3, abrogates PHYB nuclear accumulation, photobody biogenesis, and PIF3 degradation. By contrast, disrupting the interaction between PIF3 and PHYB's N-terminal module has little effect on PIF3 degradation. Together, this study demonstrates that the dimeric form of the C-terminal module plays important signaling roles by targeting PHYB to subnuclear photobodies and interacting with PIF3 to trigger its degradation.
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Affiliation(s)
- Yongjian Qiu
- Department of Botany and Plant Sciences, Institute for Integrative Genome Biology, University of California, Riverside, CA, 92521, USA
| | | | - Amit K Reddy
- Department of Biology, Duke University, Durham, NC, 27708, USA
| | - Akira Nagatani
- Department of Botany, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan
| | - Wenxiu Ma
- Department of Statistics, University of California, Riverside, CA, 92521, USA
| | - Joanne Chory
- Howard Hughes Medical Institute, Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA, 92037, USA
| | - Meng Chen
- Department of Botany and Plant Sciences, Institute for Integrative Genome Biology, University of California, Riverside, CA, 92521, USA.
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4
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Qiu Y, Pasoreck EK, Reddy AK, Nagatani A, Ma W, Chory J, Chen M. Mechanism of early light signaling by the carboxy-terminal output module of Arabidopsis phytochrome B. Nat Commun 2017; 8:1905. [PMID: 29199270 DOI: 10.1038/s41467-017-02062-6] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 11/03/2017] [Indexed: 11/08/2022] Open
Abstract
Plant phytochromes are thought to transduce light signals by mediating the degradation of phytochrome-interacting transcription factors (PIFs) through the N-terminal photosensory module, while the C-terminal module, including a histidine kinase-related domain (HKRD), does not participate in signaling. Here we show that the C-terminal module of Arabidopsis phytochrome B (PHYB) is sufficient to mediate the degradation of PIF3 specifically and to activate photosynthetic genes in the dark. The HKRD is a dimerization domain for PHYB homo and heterodimerization. A D1040V mutation, which disrupts the dimerization of HKRD and the interaction between C-terminal module and PIF3, abrogates PHYB nuclear accumulation, photobody biogenesis, and PIF3 degradation. By contrast, disrupting the interaction between PIF3 and PHYB's N-terminal module has little effect on PIF3 degradation. Together, this study demonstrates that the dimeric form of the C-terminal module plays important signaling roles by targeting PHYB to subnuclear photobodies and interacting with PIF3 to trigger its degradation.
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5
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Viczián A, Klose C, Ádám É, Nagy F. New insights of red light-induced development. Plant Cell Environ 2017; 40:2457-2468. [PMID: 27943362 DOI: 10.1111/pce.12880] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 12/04/2016] [Accepted: 12/05/2016] [Indexed: 05/14/2023]
Abstract
The red/far-red light absorbing photoreceptors phytochromes regulate development and growth and thus play an essential role in optimizing adaptation of the sessile plants to the ever-changing environment. Our understanding of how absorption of a red/far-red photon by phytochromes initiates/modifies diverse physiological responses has been steadily improving. Research performed in the last 5 years has been especially productive and led to significant conceptual changes about the mode of action of these photoreceptors. In this review, we focus on the phytochrome B photoreceptor, the major phytochrome species active in light-grown plants. We discuss how its light-independent inactivation (termed dark/thermal reversion), post-translational modification, including ubiquitination, phosphorylation and sumoylation, as well as heterodimerization with other phytochrome species modify red light-controlled physiological responses. Finally, we discuss how photobiological properties of phytochrome B enable this photoreceptor to function also as a thermosensor.
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Affiliation(s)
- András Viczián
- Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary
| | - Cornelia Klose
- Institute of Biology2/Botany, University of Freiburg, Schänzlestrasse 1, D-79104, Freiburg, Germany
| | - Éva Ádám
- Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary
| | - Ferenc Nagy
- Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726, Szeged, Hungary
- Institute of Molecular Plant Science, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3JH, UK
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Smith RW, Helwig B, Westphal AH, Pel E, Borst JW, Fleck C. Interactions Between phyB and PIF Proteins Alter Thermal Reversion Reactions in vitro. Photochem Photobiol 2017; 93:1525-1531. [PMID: 28503745 DOI: 10.1111/php.12793] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Accepted: 05/02/2017] [Indexed: 10/19/2022]
Abstract
The dynamic behavior of the plant red/far-red light photoreceptor phytochrome B (phyB) has been elucidated in natural and synthetic systems. Red light switches phyB from the inactive Pr state to the active Pfr state, a process that is reversed by far-red light. Alongside light signals, phyB activity is constrained by thermal reversion (that is prominent in the dark) and protein-protein interactions between phyB, other phytochrome molecules, and, among others, PHYTOCHROME INTERACTING FACTORs (PIFs). Requirements for phyB-PIF association have been well studied and are central to light-regulated synthetic tools. However, it is unknown whether PIF interactions influence transitions of phyB between different conformers. Here, we show that the in vitro thermal reversion of phyB involves multiple reactions. Thermal reversion of phyB in vitro is inhibited by PIF6, and this effect is observed at all temperatures tested. We analyzed our experimental data using a mathematical model containing multiple Pfr conformers, in accordance with previous findings. Remarkably, each Pfr conformer is differentially regulated by PIF6 and temperature. As a result, we speculate that in vivo phytochrome signaling networks may require similar levels of complexity to fine-tune responses to the external environment.
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Affiliation(s)
- Robert W Smith
- Laboratory of Systems & Synthetic Biology, Wageningen University & Research, Wageningen, The Netherlands.,LifeGlimmer GmbH, Berlin, Germany
| | - Britta Helwig
- Laboratory of Systems & Synthetic Biology, Wageningen University & Research, Wageningen, The Netherlands
| | - Adrie H Westphal
- Laboratory of Biochemistry, Wageningen University & Research, Wageningen, The Netherlands
| | - Eran Pel
- Laboratory of Systems & Synthetic Biology, Wageningen University & Research, Wageningen, The Netherlands
| | - Jan Willem Borst
- Laboratory of Biochemistry, Wageningen University & Research, Wageningen, The Netherlands
| | - Christian Fleck
- Laboratory of Systems & Synthetic Biology, Wageningen University & Research, Wageningen, The Netherlands
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Su J, Liu B, Liao J, Yang Z, Lin C, Oka Y. Coordination of Cryptochrome and Phytochrome Signals in the Regulation of Plant Light Responses. Agronomy 2017; 7:25. [DOI: 10.3390/agronomy7010025] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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8
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Nagano S. From photon to signal in phytochromes: similarities and differences between prokaryotic and plant phytochromes. J Plant Res 2016; 129:123-135. [PMID: 26818948 DOI: 10.1007/s10265-016-0789-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 01/03/2016] [Indexed: 06/05/2023]
Abstract
Phytochromes represent a diverse family of red/far-red-light absorbing chromoproteins which are widespread across plants, cyanobacteria, non-photosynthetic bacteria, and more. Phytochromes play key roles in regulating physiological activities in response to light, a critical element in the acclimatization to the environment. The discovery of prokaryotic phytochromes facilitated structural studies which deepened our understanding on the general mechanisms of phytochrome action. An extrapolation of this information to plant phytochromes is justified for universally conserved functional aspects, but it is also true that there are many aspects which are unique to plant phytochromes. Here I summarize some structural studies carried out to date on both prokaryotic and plant phytochromes. I also attempt to identify aspects which are common or unique to plant and prokaryotic phytochromes. Phytochrome themselves, as well as the downstream signaling pathway in plants are more complex than in their prokaryotic counterparts. Thus many structural and functional aspects of plant phytochrome remain unresolved.
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Affiliation(s)
- Soshichiro Nagano
- Institute for Plant Physiology, Justus Liebig University Giessen, Senckenbergstrasse 3, 35390, Giessen, Germany.
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9
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Su L, Hou P, Song M, Zheng X, Guo L, Xiao Y, Yan L, Li W, Yang J. Synergistic and Antagonistic Action of Phytochrome (Phy) A and PhyB during Seedling De-Etiolation in Arabidopsis thaliana. Int J Mol Sci 2015; 16:12199-212. [PMID: 26030677 PMCID: PMC4490439 DOI: 10.3390/ijms160612199] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Revised: 05/13/2015] [Accepted: 05/15/2015] [Indexed: 11/16/2022] Open
Abstract
It has been reported that Arabidopsis phytochrome (phy) A and phyB are crucial photoreceptors that display synergistic and antagonistic action during seedling de-etiolation in multiple light signaling pathways. However, the functional relationship between phyA and phyB is not fully understood under different kinds of light and in response to different intensities of such light. In this work, we compared hypocotyl elongation of the phyA-211 phyB-9 double mutant with the wild type, the phyA-211 and phyB-9 single mutants under different intensities of far-red (FR), red (R), blue (B) and white (W) light. We confirmed that phyA and phyB synergistically promote seedling de-etiolation in B-, B plus R-, W- and high R-light conditions. The correlation of endogenous ELONGATED HYPOCOTYL 5 (HY5) protein levels with the trend of hypocotyl elongation of all lines indicate that both phyA and phyB promote seedling photomorphogenesis in a synergistic manner in high-irradiance white light. Gene expression analyses of RBCS members and HY5 suggest that phyB and phyA act antagonistically on seedling development under FR light.
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Affiliation(s)
- Liang Su
- Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China.
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Pei Hou
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Meifang Song
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
- Beijing Radiation Center, Beijing 100875, China.
| | - Xu Zheng
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Lin Guo
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Yang Xiao
- Graduate School, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Lei Yan
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Wanchen Li
- Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China.
| | - Jianping Yang
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
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10
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Su L, Hou P, Song M, Zheng X, Guo L, Xiao Y, Yan L, Li W, Yang J. Synergistic and Antagonistic Action of Phytochrome (Phy) A and PhyB during Seedling De-Etiolation in Arabidopsis thaliana. Int J Mol Sci 2015. [PMID: 26030677 DOI: 10.3390/2fijms160612199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/09/2023] Open
Abstract
It has been reported that Arabidopsis phytochrome (phy) A and phyB are crucial photoreceptors that display synergistic and antagonistic action during seedling de-etiolation in multiple light signaling pathways. However, the functional relationship between phyA and phyB is not fully understood under different kinds of light and in response to different intensities of such light. In this work, we compared hypocotyl elongation of the phyA-211 phyB-9 double mutant with the wild type, the phyA-211 and phyB-9 single mutants under different intensities of far-red (FR), red (R), blue (B) and white (W) light. We confirmed that phyA and phyB synergistically promote seedling de-etiolation in B-, B plus R-, W- and high R-light conditions. The correlation of endogenous ELONGATED HYPOCOTYL 5 (HY5) protein levels with the trend of hypocotyl elongation of all lines indicate that both phyA and phyB promote seedling photomorphogenesis in a synergistic manner in high-irradiance white light. Gene expression analyses of RBCS members and HY5 suggest that phyB and phyA act antagonistically on seedling development under FR light.
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Affiliation(s)
- Liang Su
- Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China.
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Pei Hou
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Meifang Song
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
- Beijing Radiation Center, Beijing 100875, China.
| | - Xu Zheng
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Lin Guo
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Yang Xiao
- Graduate School, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Lei Yan
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Wanchen Li
- Maize Research Institute, Sichuan Agricultural University, Chengdu 611130, China.
| | - Jianping Yang
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
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Takala H, Björling A, Linna M, Westenhoff S, Ihalainen JA. Light-induced Changes in the Dimerization Interface of Bacteriophytochromes. J Biol Chem 2015; 290:16383-92. [PMID: 25971964 DOI: 10.1074/jbc.m115.650127] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Indexed: 11/06/2022] Open
Abstract
Phytochromes are dimeric photoreceptor proteins that sense red light levels in plants, fungi, and bacteria. The proteins are structurally divided into a light-sensing photosensory module consisting of PAS, GAF, and PHY domains and a signaling output module, which in bacteriophytochromes typically is a histidine kinase (HK) domain. Existing structural data suggest that two dimerization interfaces exist between the GAF and HK domains, but their functional roles remain unclear. Using mutational, biochemical, and computational analyses of the Deinococcus radiodurans phytochrome, we demonstrate that two dimerization interfaces between sister GAF and HK domains stabilize the dimer with approximately equal contributions. The existence of both dimerization interfaces is critical for thermal reversion back to the resting state. We also find that a mutant in which the interactions between the GAF domains were removed monomerizes under red light. This implies that the interactions between the HK domains are significantly altered by photoconversion. The results suggest functional importance of the dimerization interfaces in bacteriophytochromes.
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Affiliation(s)
- Heikki Takala
- From the University of Gothenburg, Department of Chemistry and Molecular Biology, Gothenburg, SE-40530 Sweden and University of Jyvaskyla, Nanoscience Center, Department of Biological and Environmental Sciences, Jyväskylä, FI-40014 Finland
| | - Alexander Björling
- From the University of Gothenburg, Department of Chemistry and Molecular Biology, Gothenburg, SE-40530 Sweden and
| | - Marko Linna
- University of Jyvaskyla, Nanoscience Center, Department of Biological and Environmental Sciences, Jyväskylä, FI-40014 Finland
| | - Sebastian Westenhoff
- From the University of Gothenburg, Department of Chemistry and Molecular Biology, Gothenburg, SE-40530 Sweden and
| | - Janne A Ihalainen
- University of Jyvaskyla, Nanoscience Center, Department of Biological and Environmental Sciences, Jyväskylä, FI-40014 Finland
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Song MF, Zhang S, Hou P, Shang HZ, Gu HK, Li JJ, Xiao Y, Guo L, Su L, Gao JW, Yang JP. Ectopic expression of a phytochrome B gene from Chinese cabbage (Brassica rapa L. ssp. pekinensis) in Arabidopsis thaliana promotes seedling de-etiolation, dwarfing in mature plants, and delayed flowering. Plant Mol Biol 2015; 87:633-43. [PMID: 25724426 DOI: 10.1007/s11103-015-0302-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Accepted: 02/18/2015] [Indexed: 05/22/2023]
Abstract
Phytochrome B (phyB) is an essential red light receptor that predominantly mediates seedling de-etiolation, shade-avoidance response, and flowering time. In this study, we isolate a full-length cDNA of PHYB, designated BrPHYB, from Chinese cabbage (Brassica rapa L. ssp. pekinensis), and we find that BrphyB protein has high amino acid sequence similarity and the closest evolutionary relationship to Arabidopsis thaliana phyB (i.e., AtphyB). Quantitative reverse transcription (RT)-PCR results indicate that the BrPHYB gene is ubiquitously expressed in different tissues under all light conditions. Constitutive expression of the BrPHYB gene in A. thaliana significantly enhances seedling de-etiolation under red- and white-light conditions, and causes dwarf stature in mature plants. Unexpectedly, overexpression of BrPHYB in transgenic A. thaliana resulted in reduced expression of gibberellins biosynthesis genes and delayed flowering under short-day conditions, whereas AtPHYB overexpression caused enhanced expression of FLOWERING LOCUS T and earlier flowering. Our results suggest that BrphyB might play an important role in regulating the development of Chinese cabbage. BrphyB and AtphyB have conserved functions during de-etiolation and vegetative plant growth and divergent functions in the regulation of flowering time.
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Affiliation(s)
- Mei-Fang Song
- Beijing Radiation Center, Beijing, 100875, People's Republic of China
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Procko C, Crenshaw CM, Ljung K, Noel JP, Chory J. Cotyledon-Generated Auxin Is Required for Shade-Induced Hypocotyl Growth in Brassica rapa. Plant Physiol 2014; 165:1285-1301. [PMID: 24891610 PMCID: PMC4081337 DOI: 10.1104/pp.114.241844] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Accepted: 06/01/2014] [Indexed: 05/20/2023]
Abstract
Plant architecture is optimized for the local light environment. In response to foliar shade or neighbor proximity (low red to far-red light), some plant species exhibit shade-avoiding phenotypes, including increased stem and hypocotyl growth, which increases the likelihood of outgrowing competitor plants. If shade persists, early flowering and the reallocation of growth resources to stem elongation ultimately affect the yield of harvestable tissues in crop species. Previous studies have shown that hypocotyl growth in low red to far-red shade is largely dependent on the photoreceptor phytochrome B and the phytohormone auxin. However, where shade is perceived in the plant and how auxin regulates growth spatially are less well understood. Using the oilseed and vegetable crop species Brassica rapa, we show that the perception of low red to far-red shade by the cotyledons triggers hypocotyl cell elongation and auxin target gene expression. Furthermore, we find that following shade perception, elevated auxin levels occur in a basipetal gradient away from the cotyledons and that this is coincident with a gradient of auxin target gene induction. These results show that cotyledon-generated auxin regulates hypocotyl elongation. In addition, we find in mature B. rapa plants that simulated shade does not affect seed oil composition but may affect seed yield. This suggests that in field settings where mutual shading between plants may occur, a balance between plant density and seed yield per plant needs to be achieved for maximum oil yield, while oil composition might remain constant.
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Affiliation(s)
- Carl Procko
- Plant Biology Laboratory (C.P., J.C.), Jack H. Skirball Center for Chemical Biology and Proteomics (C.M.C., J.P.N.), and Howard Hughes Medical Institute (C.M.C., J.P.N., J.C.), Salk Institute for Biological Studies, La Jolla, California 92037; andUmeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umea, Sweden (K.L.)
| | - Charisse Michelle Crenshaw
- Plant Biology Laboratory (C.P., J.C.), Jack H. Skirball Center for Chemical Biology and Proteomics (C.M.C., J.P.N.), and Howard Hughes Medical Institute (C.M.C., J.P.N., J.C.), Salk Institute for Biological Studies, La Jolla, California 92037; andUmeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umea, Sweden (K.L.)
| | - Karin Ljung
- Plant Biology Laboratory (C.P., J.C.), Jack H. Skirball Center for Chemical Biology and Proteomics (C.M.C., J.P.N.), and Howard Hughes Medical Institute (C.M.C., J.P.N., J.C.), Salk Institute for Biological Studies, La Jolla, California 92037; andUmeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umea, Sweden (K.L.)
| | - Joseph Patrick Noel
- Plant Biology Laboratory (C.P., J.C.), Jack H. Skirball Center for Chemical Biology and Proteomics (C.M.C., J.P.N.), and Howard Hughes Medical Institute (C.M.C., J.P.N., J.C.), Salk Institute for Biological Studies, La Jolla, California 92037; andUmeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umea, Sweden (K.L.)
| | - Joanne Chory
- Plant Biology Laboratory (C.P., J.C.), Jack H. Skirball Center for Chemical Biology and Proteomics (C.M.C., J.P.N.), and Howard Hughes Medical Institute (C.M.C., J.P.N., J.C.), Salk Institute for Biological Studies, La Jolla, California 92037; andUmeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umea, Sweden (K.L.)
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14
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Xie X, Kagawa T, Takano M. The phytochrome B/phytochrome C heterodimer is necessary for phytochrome C-mediated responses in rice seedlings. PLoS One 2014; 9:e97264. [PMID: 24853557 PMCID: PMC4031084 DOI: 10.1371/journal.pone.0097264] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Accepted: 04/16/2014] [Indexed: 01/19/2023] Open
Abstract
Background PhyC levels have been observed to be markedly lower in phyB mutants than in Arabidopsis or rice wild type etiolated seedlings, but the mechanism of this phenomenon has not been fully elucidated. Results In the present study, we investigated the mechanism by which phyB affects the protein concentration and photo-sensing abilities of phyC and demonstrated that rice phyC exists predominantly as phyB/phyC heterodimers in etiolated seedlings. PHYC-GFP protein was detected when expressed in phyA phyC mutants, but not in phyA phyB mutants, suggesting that phyC requires phyB for its photo-sensing abilities. Interestingly, when a mutant PHYB gene that has no chromophore binding site, PHYB(C364A), was introduced into phyB mutants, the phyC level was restored. Moreover, when PHYB(C364A) was introduced into phyA phyB mutants, the seedlings exhibited de-etiolation under both far-red light (FR) and red light (R) conditions, while the phyA phyB mutants were blind to both FR and R. These results are the first direct evidence that phyC is responsible for regulating seedling de-etiolation under both FR and R. These findings also suggest that phyB is indispensable for the expression and function of phyC, which depends on the formation of phyB/phyC heterodimers. Significance The present report clearly demonstrates the similarities and differences in the properties of phyC between Arabidopsis and rice and will advance our understanding of phytochrome functions in monocots and dicots.
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Affiliation(s)
- Xianzhi Xie
- Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan
- Shandong Rice Research Institute, Shandong Academy of Agricultural Sciences, Jinan, Shandong, China
| | - Takatoshi Kagawa
- Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan
| | - Makoto Takano
- Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan
- * E-mail:
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15
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Oh S, Montgomery BL. Phytochrome-induced SIG2 expression contributes to photoregulation of phytochrome signalling and photomorphogenesis in Arabidopsis thaliana. J Exp Bot 2013; 64:5457-72. [PMID: 24078666 PMCID: PMC3871806 DOI: 10.1093/jxb/ert308] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Chloroplast-localized sigma factor (SIG) proteins promote specificity of the plastid-encoded RNA polymerase. SIG2 function appears to be necessary for light-grown Arabidopsis thaliana plants. Specific photoreceptors or light-dependent factors that impact the light-induced accumulation of SIG2 have not been reported. A molecular link between phytochromes and nuclear-encoded SIG2, which impacts photomorphogenesis specifically under red (R) and far-red (FR) light, is described here. Both phyA and phyB promote SIG2 transcript accumulation. Disruption of SIG2 results in R- and FR-specific defects in the inhibition of hypocotyl elongation and cotyledon expansion, although no impairments in these responses are detected for sig2 mutants under blue (B) or white (W) light. SIG2 also impacts root elongation under W and R, and the R-dependent expression of PIF4, encoding a phytochrome-interacting factor, and HY2, which encodes a phytochrome chromophore biosynthetic enzyme. Whereas SIG2 apparently impacts the accumulation of the phytochromobilin (PΦB) phytochrome chromophore, sig2 mutants differ significantly from PΦB mutants, primarily due to wavelength-specific defects in photomorphogenesis and disruption of a distinct subset of phytochrome-dependent responses. The molecular link between phytochromes and SIG2 is likely to be an important part of the co-ordination of gene expression to maintain stoichiometry between the nuclear-encoded phytochrome apoprotein and plastid-derived PΦB, which combine to form photoactive phytochromes, and/or light-dependent SIG2 accumulation is involved in an inductive light signalling pathway co-ordinating components between nucleus and plastids.
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Affiliation(s)
- Sookyung Oh
- Department of Energy—Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
| | - Beronda L. Montgomery
- Department of Energy—Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
- * To whom correspondence should be addressed. E-mail:
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16
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Liu P, Sharrock RA. Directed dimerization: an in vivo expression system for functional studies of type II phytochromes. Plant J 2013; 75:915-926. [PMID: 23738620 DOI: 10.1111/tpj.12255] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Revised: 05/16/2013] [Accepted: 05/29/2013] [Indexed: 06/02/2023]
Abstract
Type II phytochromes (phy) in Arabidopsis form homodimers and heterodimers, resulting in a diverse collection of light-stable red/far-red (R/FR) sensing photoreceptors. We describe an in vivo protein engineering system and its use in characterizing the activities of these molecules. Using a phyB null mutant background, singly and doubly transgenic plants were generated that express fusion proteins containing the phyB-phyE N-terminal photosensory regions (NB-NE PSRs), a nuclear localization sequence, and small yeast protein domains that mediate either homodimerization or heterodimerization. Activity of NB/NB homodimers but not monomeric NB subunits in control of seedling and adult plant responses to R light is demonstrated. Heterodimers of the NB sequence with the chromophoreless NB(C357S) sequence, which mimic phyB Pfr/Pr photo-heterodimers, mediate R sensitivity in leaves and petioles but not hypocotyls. Homodimerization of the NC, ND and NE sequences and directed heterodimerization of these photosensory regions with the NB region reveal form-specific R-induced activities for different type II phy dimers. The experimental approach developed here of directed assembly of defined protein dimer combinations in vivo may be applicable to other systems.
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Affiliation(s)
- Peng Liu
- Department of Plant Sciences and Plant Pathology, Montana State University, Bozeman, MT 59717, USA
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17
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Zheng X, Wu S, Zhai H, Zhou P, Song M, Su L, Xi Y, Li Z, Cai Y, Meng F, Yang L, Wang H, Yang J. Arabidopsis phytochrome B promotes SPA1 nuclear accumulation to repress photomorphogenesis under far-red light. Plant Cell 2013; 25:115-33. [PMID: 23371951 PMCID: PMC3584529 DOI: 10.1105/tpc.112.107086] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2012] [Revised: 12/10/2012] [Accepted: 12/19/2012] [Indexed: 05/19/2023]
Abstract
Phytochrome A (phyA) is the primary photoreceptor mediating deetiolation under far-red (FR) light, whereas phyB predominantly regulates light responses in red light. SUPPRESSOR OF PHYA-105 (SPA1) forms an E3 ubiquitin ligase complex with CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), which is responsible for the degradation of various photomorphogenesis-promoting factors, resulting in desensitization to light signaling. However, the role of phyB in FR light signaling and the regulatory pathway from light-activated phytochromes to the COP1-SPA1 complex are largely unknown. Here, we confirm that PHYB overexpression causes an etiolation response with reduced ELONGATED HYPOCOTYL5 (HY5) accumulation under FR light. Notably, phyB exerts its nuclear activities and promotes seedling etiolation in both the presence and absence of phyA in response to FR light. PhyB acts upstream of SPA1 and is functionally dependent on it in FR light signaling. PhyB interacts and forms a protein complex with SPA1, enhancing its nuclear accumulation under FR light. During the dark-to-FR transition, phyB is rapidly imported into the nucleus and facilitates nuclear SPA1 accumulation. These findings support the notion that phyB plays a role in repressing FR light signaling. Activity modulation of the COP1-SPA E3 complex by light-activated phytochromes is an effective and pivotal regulatory step in light signaling.
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Affiliation(s)
- Xu Zheng
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
- Graduate School, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Suowei Wu
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Huqu Zhai
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Peng Zhou
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Meifang Song
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Liang Su
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Yulin Xi
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
- Graduate School, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Zhiyong Li
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Yingfan Cai
- College of Bio-information, Chongqing University of Posts and Telecommunication, Chongqing 400065, China
| | - Fanhua Meng
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Li Yang
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
| | - Haiyang Wang
- College of Life Sciences, Capital Normal University, Beijing 100048, China
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520
| | - Jianping Yang
- Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China
- Address correspondence to
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18
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Oka Y, Ono Y, Toledo-Ortiz G, Kokaji K, Matsui M, Mochizuki N, Nagatani A. Arabidopsis phytochrome a is modularly structured to integrate the multiple features that are required for a highly sensitized phytochrome. Plant Cell 2012; 24:2949-62. [PMID: 22843485 PMCID: PMC3426125 DOI: 10.1105/tpc.111.094201] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Phytochrome is a red (R)/far-red (FR) light-sensing photoreceptor that regulates various aspects of plant development. Among the members of the phytochrome family, phytochrome A (phyA) exclusively mediates atypical phytochrome responses, such as the FR high irradiance response (FR-HIR), which is elicited under prolonged FR. A proteasome-based degradation pathway rapidly eliminates active Pfr (the FR-absorbing form of phyA) under R. To elucidate the structural basis for the phyA-specific properties, we systematically constructed 16 chimeric phytochromes in which each of four parts of the phytochrome molecule, namely, the N-terminal extension plus the Per/Arnt/Sim domain (N-PAS), the cGMP phosphodiesterase/adenyl cyclase/FhlA domain (GAF), the phytochrome domain (PHY), and the entire C-terminal half, was occupied by either the phyA or phytochrome B sequence. These phytochromes were expressed in transgenic Arabidopsis thaliana to examine their physiological activities. Consequently, the phyA N-PAS sequence was shown to be necessary and sufficient to promote nuclear accumulation under FR, whereas the phyA sequence in PHY was additionally required to exhibit FR-HIR. Furthermore, the phyA sequence in PHY alone substantially increased the light sensitivity to R. In addition, the GAF phyA sequence was important for rapid Pfr degradation. In summary, distinct structural modules, each of which confers different properties to phyA, are assembled on the phyA molecule.
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Affiliation(s)
- Yoshito Oka
- Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan
- Plant Functional Genomics Research Group, Plant Science Center, RIKEN Yokohama Institute, Tsurumiku, Yokohama, Kanagawa 2300-0045, Japan
| | - Yuya Ono
- Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan
| | - Gabriela Toledo-Ortiz
- Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan
| | - Keio Kokaji
- Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan
| | - Minami Matsui
- Plant Functional Genomics Research Group, Plant Science Center, RIKEN Yokohama Institute, Tsurumiku, Yokohama, Kanagawa 2300-0045, Japan
| | - Nobuyoshi Mochizuki
- Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan
| | - Akira Nagatani
- Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan
- Address correspondence to
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19
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Leivar P, Monte E, Cohn MM, Quail PH. Phytochrome signaling in green Arabidopsis seedlings: impact assessment of a mutually negative phyB-PIF feedback loop. Mol Plant 2012; 5:734-49. [PMID: 22492120 PMCID: PMC3355348 DOI: 10.1093/mp/sss031] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Accepted: 02/20/2012] [Indexed: 05/18/2023]
Abstract
The reversibly red (R)/far-red (FR)-light-responsive phytochrome (phy) photosensory system initiates both the deetiolation process in dark-germinated seedlings upon first exposure to light, and the shade-avoidance process in fully deetiolated seedlings upon exposure to vegetational shade. The intracellular signaling pathway from the light-activated photoreceptor conformer (Pfr) to the transcriptional network that drives these responses involves direct, physical interaction of Pfr with a small subfamily of bHLH transcription factors, termed Phy-Interacting Factors (PIFs), which induces rapid PIF proteolytic degradation. In addition, there is evidence of further complexity in light-grown seedlings, whereby phyB-PIF interaction reciprocally induces phyB degradation, in a mutually-negative, feedback-loop configuration. Here, to assess the relative contributions of these antagonistic activities to the net phenotypic readout in light-grown seedlings, we have examined the magnitude of the light- and simulated-shade-induced responses of a pentuple phyBpif1pif3pif4pif5 (phyBpifq) mutant and various multiple pif-mutant combinations. The data (1) reaffirm that phyB is the predominant, if not exclusive, photoreceptor imposing the inhibition of hypocotyl elongation in deetiolating seedlings in response to prolonged continuous R irradiation and (2) show that the PIF quartet (PIF1, PIF3, PIF4, and PIF5) retain and exert a dual capacity to modulate hypocotyl elongation under these conditions, by concomitantly promoting cell elongation through intrinsic transcriptional-regulatory activity, and reducing phyB-inhibitory capacity through feedback-loop-induced phyB degradation. In shade-exposed seedlings, immunoblot analysis shows that the shade-imposed reduction in Pfr levels induces increases in the abundance of PIF3, and mutant analysis indicates that PIF3 acts, in conjunction with PIF4 and PIF5, to promote the known shade-induced acceleration of hypocotyl elongation. Conversely, although the quadruple pifq mutant displays clearly reduced hypocotyl elongation compared to wild-type in response to prolonged shade, immunoblot analysis detects no elevation in phyB levels in the mutant seedlings compared to the wild-type during the majority of the shade-induced growth period, and phyB levels are not robustly correlated with the growth phenotype across the pif-mutant combinations compared. These results suggest that PIF feedback modulation of phyB abundance does not play a dominant role in modulating the magnitude of the PIF-promoted, shade-responsive phenotype under these conditions. In seedlings grown under diurnal light-dark cycles, the data show that FR-pulse-induced removal of Pfr at the beginning of the dark period (End-of-Day-FR (EOD-FR) treatment) results in longer hypocotyls relative to no EOD-FR treatment and that this effect is attenuated in the pif-mutant combinations tested. This result similarly indicates that the PIF quartet members are capable of intrinsically promoting hypocotyl cell elongation in light-grown plants, independently of the effects of PIF feedback modulation of photoactivated-phyB abundance.
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Affiliation(s)
- Pablo Leivar
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
- United States Department of Agriculture, Plant Gene Expression Center, Albany, CA 94710, USA
- Department of Molecular Genetics, Center for Research in Agricultural Genomics (CRAG) CSIC-IRTA-UAB-UB, Campus UAB, Bellaterra (Cerdanyola del Vallès), 08193 Barcelona, Spain
| | - Elena Monte
- Department of Molecular Genetics, Center for Research in Agricultural Genomics (CRAG) CSIC-IRTA-UAB-UB, Campus UAB, Bellaterra (Cerdanyola del Vallès), 08193 Barcelona, Spain
| | - Megan M. Cohn
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
- United States Department of Agriculture, Plant Gene Expression Center, Albany, CA 94710, USA
| | - Peter H. Quail
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
- United States Department of Agriculture, Plant Gene Expression Center, Albany, CA 94710, USA
- To whom correspondence should be addressed. E-mail , tel. (510) 559-5900, fax (510) 559-5678
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20
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Prasad BRV, Kumar SV, Nandi A, Chattopadhyay S. Functional interconnections of HY1 with MYC2 and HY5 in Arabidopsis seedling development. BMC Plant Biol 2012; 12:37. [PMID: 22424472 PMCID: PMC3353174 DOI: 10.1186/1471-2229-12-37] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Accepted: 03/17/2012] [Indexed: 05/19/2023]
Abstract
Arabidopsis seedling development is controlled by many regulatory genes involved in multiple signaling pathways. The functional relationships of these genes working in multiple signaling cascades have started to be unraveled. Arabidopsis HY1/HO1 is a rate-limiting enzyme involved in biosynthesis of phytochrome chromophore. HY5 (a bZIP protein) promotes photomorphogenesis, however ZBF1/MYC2 (a bHLH protein) works as a negative regulator of photomorphogenic growth and light regulated gene expression. Further, MYC2 and HY1 have been shown to play important roles in jasmonic acid (JA) signaling pathways. Here, we show the genetic interactions of HY1 with two key transcription factor genes of light signaling, HY5 and MYC2, in Arabidopsis seedling development. Our studies reveal that although HY1 acts in an additive manner with HY5, it is epistatic to MYC2 in light-mediated seedling growth and gene expression. This study further demonstrates that HY1 additively or synergistically functions with HY5, however it works upstream to MYC2 in JA signaling pathways. Taken together, this study demonstrates the functional interrelations of HY1, MYC2 and HY5 in light and JA signaling pathways.
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Affiliation(s)
| | - Selva V Kumar
- National Institute of Plant Genome Research, New Delhi, India
| | - Ashis Nandi
- School of Life Sciences, Jawharlal Neheru University, New Delhi, India
| | - Sudip Chattopadhyay
- Department of Biotechnology, National Institute of Technology, Mahatma Gandhi Avenue, Durgapur 713209, West Bengal, India
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21
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Oka Y, Kong SG, Matsushita T. A non-covalently attached chromophore can mediate phytochrome B signaling in Arabidopsis. Plant Cell Physiol 2011; 52:2088-102. [PMID: 22006939 DOI: 10.1093/pcp/pcr139] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Phytochrome B (phyB) is the major informational photoreceptor in light-grown plants. The phyB polypeptide is folded into two domains, the N-terminal domain and the C-terminal domain. The N-terminal domain covalently binds to the chromophore via a particular cysteine residue, which allows the holoprotein to absorb light and undergo a photoreversible conformational change. The N-terminal domain of phyB interacts with transcription factors, such as PIF3 (PHYTOCHROME-INTERACTING FACTOR 3), to transduce the light signal to downstream components. Since substitution of the chromophore attachment site, Cys357, with alanine (C357A) abolishes the biological activity of Arabidopsis phyB, the covalent attachment with the chromophore is widely assumed to be necessary for phyB signal transduction. In this study, we show that Arabidopsis phyB is capable of transducing signals with a non-covalently retained chromophore. Substituting the Tyr276 residue of phyB with histidine (Y276H) is known to confer constitutive phyB signaling. PhyB containing both Y276H and C357A substitutions exhibited light-independent biological activity in transgenic Arabidopsis plants in a chromophore-dependent manner. Spectrophotometric analysis showed that the N-terminal domain of phyB containing just the C357A substitution could retain the chromophore non-covalently. The N-terminal domain containing both the Y276H and C357A substitutions interacted with PIF3 in a light-independent but chromophore-dependent fashion in yeast two-hybrid assays. From these results, we conclude that the constitutive phyB signaling conferred by Y276H requires the chromophore, but that the chromophore does not need to be covalently bonded to phyB.
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Affiliation(s)
- Yoshito Oka
- RIKEN Plant Science Center, Yokohama, 230-0045 Japan
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22
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Clack T, Shokry A, Moffet M, Liu P, Faul M, Sharrock RA. Obligate heterodimerization of Arabidopsis phytochromes C and E and interaction with the PIF3 basic helix-loop-helix transcription factor. Plant Cell 2009; 21:786-99. [PMID: 19286967 PMCID: PMC2671712 DOI: 10.1105/tpc.108.065227] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2008] [Revised: 02/17/2009] [Accepted: 03/02/2009] [Indexed: 05/18/2023]
Abstract
Phytochromes are dimeric chromoproteins that regulate plant responses to red (R) and far-red (FR) light. The Arabidopsis thaliana genome encodes five phytochrome apoproteins: type I phyA mediates responses to FR, and type II phyB-phyE mediate shade avoidance and classical R/FR-reversible responses. In this study, we describe the complete in vivo complement of homodimeric and heterodimeric type II phytochromes. Unexpectedly, phyC and phyE do not homodimerize and are present in seedlings only as heterodimers with phyB and phyD. Roles in light regulation of hypocotyl length, leaf area, and flowering time are demonstrated for heterodimeric phytochromes containing phyC or phyE. Heterodimers of phyC and chromophoreless phyB are inactive, indicating that phyC subunits require spectrally intact dimer partners to be active themselves. Consistent with the obligate heterodimerization of phyC and phyE, phyC is made unstable by removal of its phyB binding partner, and overexpression of phyE results in accumulation of phyE monomers. Following a pulse of red light, phyA, phyB, phyC, and phyD interact in vivo with the PHYTOCHROME INTERACTING FACTOR3 basic helix-loop-helix transcription factor, and this interaction is FR reversible. Therefore, most or all of the type I and type II phytochromes, including heterodimeric forms, appear to function through PIF-mediated pathways. These findings link an unanticipated diversity of plant R/FR photoreceptor structures to established phytochrome signaling mechanisms.
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Affiliation(s)
- Ted Clack
- Department of Plant Sciences and Plant Pathology, Montana State University, Bozeman, Montana 59717, USA
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Oka Y, Matsushita T, Mochizuki N, Quail PH, Nagatani A. Mutant screen distinguishes between residues necessary for light-signal perception and signal transfer by phytochrome B. PLoS Genet 2008; 4:e1000158. [PMID: 18704165 DOI: 10.1371/journal.pgen.1000158] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Accepted: 07/10/2008] [Indexed: 01/21/2023] Open
Abstract
The phytochromes (phyA to phyE) are a major plant photoreceptor family that regulate a diversity of developmental processes in response to light. The N-terminal 651–amino acid domain of phyB (N651), which binds an open tetrapyrrole chromophore, acts to perceive and transduce regulatory light signals in the cell nucleus. The N651 domain comprises several subdomains: the N-terminal extension, the Per/Arnt/Sim (PAS)-like subdomain (PLD), the cGMP phosphodiesterase/adenyl cyclase/FhlA (GAF) subdomain, and the phytochrome (PHY) subdomain. To define functional roles for these subdomains, we mutagenized an Arabidopsis thaliana line expressing N651 fused in tandem to green fluorescent protein, β-glucuronidase, and a nuclear localization signal. A large-scale screen for long hypocotyl mutants identified 14 novel intragenic missense mutations in the N651 moiety. These new mutations, along with eight previously identified mutations, were distributed throughout N651, indicating that each subdomain has an important function. In vitro analysis of the spectral properties of these mutants enabled them to be classified into two principal classes: light-signal perception mutants (those with defective spectral activity), and signaling mutants (those normal in light perception but defective in intracellular signal transfer). Most spectral mutants were found in the GAF and PHY subdomains. On the other hand, the signaling mutants tend to be located in the N-terminal extension and PLD. These observations indicate that the N-terminal extension and PLD are mainly involved in signal transfer, but that the C-terminal GAF and PHY subdomains are responsible for light perception. Among the signaling mutants, R110Q, G111D, G112D, and R325K were particularly interesting. Alignment with the recently described three-dimensional structure of the PAS-GAF domain of a bacterial phytochrome suggests that these four mutations reside in the vicinity of the phytochrome light-sensing knot. Adapting to the light environment, plants have evolved several photoreceptors, of which the phytochromes are specialized in perceiving the red and far-red light region of the spectrum. Although phytochrome was first discovered in plants, the phytochrome species are present in several organisms, including bacteria. The mechanisms by which phytochromes transduce light signals to downstream components are most well studied in plants. Upon light activation, phytochromes translocate from the cytoplasm into nucleus and regulate the gene expression network through interaction with nuclear transcription factors. The phytochrome molecule can be divided into two major domains: the N-terminal moiety, which is responsible for the light perception, and the C-terminal moiety. Although the C-terminal moiety was though to be involved in signal transduction, it has recently been shown that the N-terminal moiety has a role not only in the light perception, but also in light signal transfer to the downstream network. However, no signaling motifs have been found in the N-terminal moiety. In this study, we analyzed intragenic mutations derived from a genetic screen and found a cluster of residues necessary for signal transduction in a small region neighboring the light-sensing chromophore moiety on the three-dimensional structure. This is an important step towards understanding how a major plant photoreceptor, phytochrome, intramolecularly processes the light signal to trigger diverse physiological responses.
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Leivar P, Monte E, Al-Sady B, Carle C, Storer A, Alonso JM, Ecker JR, Quail PH. The Arabidopsis phytochrome-interacting factor PIF7, together with PIF3 and PIF4, regulates responses to prolonged red light by modulating phyB levels. Plant Cell 2008; 20:337-52. [PMID: 18252845 PMCID: PMC2276449 DOI: 10.1105/tpc.107.052142] [Citation(s) in RCA: 281] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2007] [Revised: 11/19/2007] [Accepted: 01/15/2008] [Indexed: 05/18/2023]
Abstract
We show that a previously uncharacterized Arabidopsis thaliana basic helix-loop-helix (bHLH) phytochrome interacting factor (PIF), designated PIF7, interacts specifically with the far-red light-absorbing Pfr form of phyB through a conserved domain called the active phyB binding motif. Similar to PIF3, upon light exposure, PIF7 rapidly migrates to intranuclear speckles, where it colocalizes with phyB. However, in striking contrast to PIF3, this process is not accompanied by detectable light-induced phosphorylation or degradation of PIF7, suggesting that the consequences of interaction with photoactivated phyB may differ among PIFs. Nevertheless, PIF7 acts similarly to PIF3 in prolonged red light as a weak negative regulator of phyB-mediated seedling deetiolation. Examination of pif3, pif4, and pif7 double mutant combinations shows that their moderate hypersensitivity to extended red light is additive. We provide evidence that the mechanism by which these PIFs operate on the phyB signaling pathway under prolonged red light is through maintaining low phyB protein levels, in an additive or synergistic manner, via a process likely involving the proteasome pathway. These data suggest that the role of these phyB-interacting bHLH factors in modulating seedling deetiolation in prolonged red light may not be as phy-activated signaling intermediates, as proposed previously, but as direct modulators of the abundance of the photoreceptor.
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Affiliation(s)
- Pablo Leivar
- Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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Al-Sady B, Kikis EA, Monte E, Quail PH. Mechanistic duality of transcription factor function in phytochrome signaling. Proc Natl Acad Sci U S A 2008; 105:2232-7. [PMID: 18245378 DOI: 10.1073/pnas.0711675105] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The phytochrome (phy) family of sensory photoreceptors (phyA-E in Arabidopsis) elicit changes in gene expression after light-induced migration to the nucleus, where they interact with basic helix-loop-helix transcription factors, such as phytochrome-interacting factor 3 (PIF3). The mechanism by which PIF3 relays phy signals, both early after initial light exposure and later during long-term irradiation, is not understood. Using transgenically expressed PIF3 variants, carrying site-specific amino acid substitutions that block the protein from binding either to DNA, phyA, and/or phyB, we examined the involvement of PIF3 in early, phy-induced marker gene expression and in modulating long-term, phy-imposed inhibition of hypocotyl cell elongation under prolonged, continuous irradiation. We describe an unanticipated dual mechanism of PIF3 action that involves the temporal uncoupling of its two most central molecular functions. We find that in early signaling, PIF3 acts positively as a transcription factor, exclusively requiring its DNA-binding capacity. Contrary to previous proposals, PIF3 functions as a constitutive coactivator in this process, without the need for phy binding and subsequent phy-induced modifications. This finding implies that another factor(s) is conditionally activated by phy and functions in concert with PIF3, to induce target gene transcription. In contrast, during long-term irradiations, PIF3 acts exclusively through its phyB-interacting capacity to control hypocotyl cell elongation, independently of its ability to bind DNA. Unexpectedly, PIF3 uses this capacity to regulate phyB protein abundance (and thereby global photosensory sensitivity) to modulate this long-term response rather than participating directly in the transduction chain as a signaling intermediate.
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Abstract
Phytochromes are red/far-red light photoreceptors that convert the information contained in external light into biological signals. The decoding process starts with the perception of red light, which occurs through photoisomerization of a chromophore located within the phytochrome, leading to structural changes that include the disruption of intramolecular interactions between the N- and C-terminal domains of the phytochrome. This disruption exposes surfaces required for interactions with other proteins. In contrast, the perception of far-red light reverses the photoisomerization, restores the intramolecular interaction, and closes the interacting surfaces. Light information represented by the concentration of opened interacting surfaces is converted into biological signals through the modulating activity of interacting proteins. This review summarizes plant phytochromes, phytochrome-interacting proteins, and signal transmission from phytochromes to their interacting proteins.
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Affiliation(s)
- Gabyong Bae
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
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Su YS, Lagarias JC. Light-independent phytochrome signaling mediated by dominant GAF domain tyrosine mutants of Arabidopsis phytochromes in transgenic plants. Plant Cell 2007; 19:2124-39. [PMID: 17660358 PMCID: PMC1955707 DOI: 10.1105/tpc.107.051516] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The photoreversibility of plant phytochromes enables continuous surveillance of the ambient light environment. Through expression of profluorescent, photoinsensitive Tyr-to-His mutant alleles of Arabidopsis thaliana phytochrome B (PHYB(Y276H)) and Arabidopsis phytochrome A (PHYA(Y242H)) in transgenic Arabidopsis plants, we demonstrate that photoconversion is not a prerequisite for phytochrome signaling. PHYB(Y276H)-expressing plants exhibit chromophore-dependent constitutive photomorphogenesis, light-independent phyB(Y276H) nuclear localization, constitutive activation of genes normally repressed in darkness, and light-insensitive seed germination. Fluence rate analyses of transgenic plants expressing PHYB(Y276H), PHYA(Y242H), and other Y(GAF) mutant alleles of PHYB demonstrate that a range of altered light-signaling activities are associated with mutation of this residue. We conclude that the universally conserved GAF domain Tyr residue, with which the bilin chromophore is intimately associated, performs a critical role in coupling light perception to signal transduction by plant phytochromes.
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Affiliation(s)
- Yi-shin Su
- Section of Molecular and Cellular Biology, University of California, Davis, California 95616, USA
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Casal JJ, Yanovsky MJ, Luppi JP. Two Photobiological Pathways of Phytochrome A Activity, Only One of Which Shows Dominant Negative Suppression by Phytochrome B. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2000)0710481tppopa2.0.co2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Usami T, Matsushita T, Oka Y, Mochizuki N, Nagatani A. Roles for the N- and C-terminal domains of phytochrome B in interactions between phytochrome B and cryptochrome signaling cascades. Plant Cell Physiol 2007; 48:424-33. [PMID: 17251203 DOI: 10.1093/pcp/pcm012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Plants fine-tune light responses through interactions between photoreceptors. We have previously reported that the greening of Arabidopsis thaliana roots is regulated synergistically by phytochromes and cryptochromes. In the present study, we investigated the functions of the N- and C-terminal domains of phytochrome B (phyB) in the interactions between phyB and cryptochrome signaling cascades. Transgenic Arabidopsis expressing the phyB N-terminal domain fused to green fluorescent protein (GFP), beta-glucuronidase (GUS) and the nuclear localization signal (NLS) showed intense root greening under blue light, indicating that the C-terminal domain was dispensable for the synergistic interaction in the induction of root greening. However, root greening under red light was substantially reduced in the absence of the C-terminal domain. This effect was opposite to the previous observation that removal of the C-terminal domain enhanced the signaling activity of phyB in the inhibition of hypocotyl elongation. In addition, we found that overexpression of the isolated C-terminal domain of phyB enhanced the blue light response not only for root greening but also for the inhibition of hypocotyl elongation. Analysis of this activity on various photoreceptor mutant backgrounds demonstrated that the isolated C-terminal domain enhanced cryptochrome signaling. In summary, these results demonstrate that different domains of phyB can play various roles which are dependent on light conditions as well as on the specific physiological response.
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Affiliation(s)
- Takeshi Usami
- Department of Botany, Graduate School of Science, Kyoto University, Sakyo-Ku, Kyoto, 606-8502, Japan
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Torres-Galea P, Huang LF, Chua NH, Bolle C. The GRAS protein SCL13 is a positive regulator of phytochrome-dependent red light signaling, but can also modulate phytochrome A responses. Mol Genet Genomics 2006; 276:13-30. [PMID: 16680434 DOI: 10.1007/s00438-006-0123-y] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Accepted: 03/25/2006] [Indexed: 01/27/2023]
Abstract
Phytochrome photoreceptors enable plants to perceive divergent light signals leading to adaptive changes in response to differing environmental conditions. However, the mechanism of light signal transduction is not fully understood. Here we report the identification of a new signaling intermediate from Arabidopsis thaliana, Scarecrow-like (SCL)13, which serves as a positive regulator of continuous red light signals downstream of phytochrome B (phyB). SCL13 antisense lines exhibit reduced sensitivity towards red light, but only a distinct subset of phyB-mediated responses is affected, indicating that SCL13 executes its major role in hypocotyl elongation during de-etiolation. Genetic evidence suggests that SCL13 is also needed to modulate phytochrome A (phyA) signal transduction in a phyB-independent way. The SCL13 protein is localized in the cytoplasm, but can also be detected in the nucleus. Overexpression of both a nuclear and cytoplasmic localized SCL13 protein leads to a hypersensitive phenotype under red light indicating that SCL13 is biologically active in both compartments. SCL13 is a member of the plant-specific GRAS protein family, which is involved in various different developmental and signaling pathways. A previously identified phytochrome A signaling intermediate, PAT1, belongs to the same subbranch of GRAS proteins as SCL13. Although both proteins are involved in phytochrome signaling, each is specific for a different light condition and regulates a different subset of responses.
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Affiliation(s)
- Patricia Torres-Galea
- Department für Biologie I/Bereich Botanik, Ludwig-Maximilians-University, Menzinger Str. 67, 80638, Munich, Germany
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Chen M, Ni M. RED AND FAR-RED INSENSITIVE 2, a RING-domain zinc finger protein, mediates phytochrome-controlled seedling deetiolation responses. Plant Physiol 2006; 140:457-65. [PMID: 16384903 PMCID: PMC1361316 DOI: 10.1104/pp.105.073163] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Revised: 11/19/2005] [Accepted: 11/29/2005] [Indexed: 05/04/2023]
Abstract
Light is arguably the most important resource for plants, and an array of photosensory pigments enables plants to develop optimally in a broad range of ambient-light conditions. The red- and far-red-light-absorbing photosensory pigments or phytochromes (phy) regulate seedling deetiolation responses, photoperiodic flowering, and circadian rhythm. We have identified a long hypocotyl mutant under red and far-red light, rfi2-1 (red and far-red insensitive 2 to 1). rfi2-1 was also impaired in phytochrome-mediated end-of-day far-red light response, cotyledon expansion, far-red light block of greening, and light-induced expression of CHLOROPHYLL A/B BINDING PROTEIN 3 and CHALCONE SYNTHASE. Introduction of rfi2-1 mutation into phyB-9 or phyA-211 did not enhance or suppress the long hypocotyl phenotype of phyB-9 or phyA-211 under red or far-red light, respectively, and RFI2 likely functions downstream of phyB or phyA. RFI2 was identified through the segregation of two T-DNA insertions into different recombinant lines, genetic rescue, and phenotypic characterization of a second mutant allele rfi2-2. RFI2 encodes a protein with a C3H2C3-type zinc finger or RING domain known to mediate protein-protein or protein-DNA interactions, and RFI2 is localized to the nucleus. RFI2 therefore reveals a signaling step that mediates phytochrome control of seedling deetiolation.
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Affiliation(s)
- Mingjie Chen
- Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108, USA
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Sang Y, Li QH, Rubio V, Zhang YC, Mao J, Deng XW, Yang HQ. N-terminal domain-mediated homodimerization is required for photoreceptor activity of Arabidopsis CRYPTOCHROME 1. Plant Cell 2005; 17:1569-84. [PMID: 15805487 PMCID: PMC1091775 DOI: 10.1105/tpc.104.029645] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2004] [Accepted: 01/19/2005] [Indexed: 05/18/2023]
Abstract
Cryptochromes (CRY) are blue light receptors that share sequence similarity with photolyases, flavoproteins that catalyze the repair of UV light-damaged DNA. Transgenic Arabidopsis thaliana seedlings expressing the C-terminal domains of the Arabidopsis CRY fused to beta-glucuronidase (GUS) display a constitutive photomorphogenic (COP) phenotype, indicating that the signaling mechanism of Arabidopsis CRY is mediated through the C-terminal domain. The role of the Arabidopsis CRY N-terminal photolyase-like domain in CRY action remains poorly understood. Here, we report the essential role of the Arabidopsis CRY1 N-terminal domain (CNT1) in the light activation of CRY1 photoreceptor activity. Yeast two-hybrid assay, in vitro binding, in vivo chemical cross-linking, gel filtration, and coimmunoprecipitation studies indicate that CRY1 homodimerizes in a light-independent manner. Mutagenesis and transgenic studies demonstrate that CNT1-mediated dimerization is required for light activation of the C-terminal domain of CRY1 (CCT1). Transgenic data and native gel electrophoresis studies suggest that multimerization of GUS is both responsible and required for mediating a COP phenotype on fusion to CCT1. These results indicate that the properties of the GUS multimer are analogous to those of the light-modified CNT1 dimer. Irradiation with blue light modifies the properties of the CNT1 dimer, resulting in a change in CCT1, activating CCT1, and eventually triggering the CRY1 signaling pathway.
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Affiliation(s)
- Yi Sang
- National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
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Abstract
Higher plants monitor changes in the ambient light environment using three major classes of photoreceptors: the red/far-red-absorbing phytochromes, the blue/UV-A-absorbing cryptochromes, and phototropins. These photoreceptors mediate various photoresponses, ranging from seed germination, to seedling de-etiolation, stem elongation, leaf expansion, floral initiation, phototropic bending of organs, intracellular movement of chloroplast, and stomata opening. Here I briefly review the distinct and overlapping physiological functions of these photoreceptors and highlight recent progress that provided significant insights into their signaling mechanisms, particularly from a structure-function perspective. This review focuses on the early photochemical and biochemical events that lead to photoreceptor activation and signaling initiation.
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Affiliation(s)
- Haiyang Wang
- Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, New York 14853, USA
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Monte E, Tepperman JM, Al-Sady B, Kaczorowski KA, Alonso JM, Ecker JR, Li X, Zhang Y, Quail PH. The phytochrome-interacting transcription factor, PIF3, acts early, selectively, and positively in light-induced chloroplast development. Proc Natl Acad Sci U S A 2004; 101:16091-8. [PMID: 15505214 PMCID: PMC528976 DOI: 10.1073/pnas.0407107101] [Citation(s) in RCA: 224] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The phytochrome (phy) family of sensory photoreceptors transduce informational light signals to selected nuclear genes, inducing plant growth and developmental responses appropriate to the environment. Existing data suggest that one signaling pathway by which this occurs involves direct, intranuclear interaction of the photoactivated phy molecule with PIF3, a basic helix-loop-helix transcription factor. Here, we provide evidence from recently identified pif3 mutant alleles that PIF3 is necessary for early chloroplast greening and rapid phy-induced expression of nuclear genes encoding chloroplast components upon first exposure of seedlings to light. Therefore, these data indicate that PIF3 functions to transduce phy signals to genes involved in a critical facet of the early seedling deetiolation process, the generation of a functional photosynthetic apparatus. When transgenically expressed GUS:PIF3 fusion protein constructs were used, we found that PIF3 protein levels are rapidly and reversibly modulated by the photoreceptor over diurnal cycles in Arabidopsis seedlings. The PIF3 protein declines rapidly to a basal steady-state level upon initial light exposure, but reaccumulates to preirradiation levels in darkness during the subsequent night period. These data suggest that PIF3 may function in early phy signaling at the dark-to-light transition, not only during initial seedling deetiolation, but daily at dawn under diurnal light-dark cycles.
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Affiliation(s)
- Elena Monte
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
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Oka Y, Matsushita T, Mochizuki N, Suzuki T, Tokutomi S, Nagatani A. Functional analysis of a 450-amino acid N-terminal fragment of phytochrome B in Arabidopsis. Plant Cell 2004; 16:2104-16. [PMID: 15273294 PMCID: PMC519201 DOI: 10.1105/tpc.104.022350] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2004] [Accepted: 05/31/2004] [Indexed: 05/20/2023]
Abstract
Phytochrome, a major photoreceptor in plants, consists of two domains: the N-terminal photosensory domain and the C-terminal domain. Recently, the 651-amino acid photosensory domain of phytochrome B (phyB) has been shown to act as a functional photoreceptor in the nucleus. The phytochrome (PHY) domain, which is located at the C-terminal end of the photosensory domain, is required for the spectral integrity of phytochrome; however, little is known about the signal transduction activity of this domain. Here, we have established transgenic Arabidopsis thaliana lines expressing an N-terminal 450-amino acid fragment of phyB (N450) lacking the PHY domain on a phyB-deficient background. Analysis of these plants revealed that N450 can act as an active photoreceptor when attached to a short nuclear localization signal and beta-glucuronidase. In vitro spectral analysis of reconstituted chromopeptides further indicated that the stability of the N450 Pfr form, an active form of phytochrome, is markedly reduced in comparison with the Pfr form of full-length phyB. Consistent with this, plants expressing N450 failed to respond to intermittent light applied at long intervals, indicating that N450 Pfr is short-lived in vivo. Taken together, our findings show that the PHY domain is dispensable for phyB signal transduction but is required for stabilizing the Pfr form of phyB.
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Affiliation(s)
- Yoshito Oka
- Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-Ku, Kyoto 606-8502, Japan
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Abstract
Phytochromes are red- and far-red-sensing photoreceptors that detect the quantity, quality, and duration of light throughout the entire life cycle of plants. Phytochromes accumulate in the cytoplasm in the dark. As one of the earliest responses after light illumination, phytochromes localize to the nucleus where they become associated with discrete nuclear bodies (NBs). Here, we describe the steady-state dynamics of Arabidopsis phytochrome B (phyB) localization in response to different light conditions and define four phyB subnuclear localization patterns: diffuse nuclear localization, small and numerous NBs only, both small and large NBs, and large NBs only. We show that phyB nuclear import is not sufficient for phyB NB formation. Rather, phyB accumulation in NBs is mainly determined by the percentage of the total amount of phyB protein that is in the active phyB conformer, with large NBs always correlating with strong phyB responses. A genetic screen to identify determinants required for subnuclear localization of phyB resulted in several phyB mutants, mutants deficient in phytochrome chromophore biosynthesis, and mutations in at least one previously uninvestigated locus. This study lays the groundwork for future investigations to identify the molecular mechanisms of light-regulated partitioning of plant photoreceptors to discrete subnuclear domains.
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Affiliation(s)
- Meng Chen
- Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA
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Matsushita T, Mochizuki N, Nagatani A. Dimers of the N-terminal domain of phytochrome B are functional in the nucleus. Nature 2003; 424:571-4. [PMID: 12891362 DOI: 10.1038/nature01837] [Citation(s) in RCA: 211] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2003] [Accepted: 05/19/2003] [Indexed: 11/09/2022]
Abstract
A plant modulates its developmental processes in response to light by several informational photoreceptors such as phytochrome. Phytochrome is a dimeric chromoprotein which regulates various aspects of plant development from seed germination to flowering. Upon absorption of red light, phytochrome translocates from the cytoplasm to the nucleus, and regulates gene expression through interaction with transcription factors such as PIF3 (refs 5-7). The phytochrome polypeptide has two domains: the amino-terminal photosensory domain with a chromophore and the carboxy-terminal domain which contains signalling motifs such as a kinase domain. The latter is widely believed to transduce the signal to downstream components. Here we show that the C-terminal domain of Arabidopsis phytochrome B (phyB), which is known as the most important member of the phytochrome family, is not directly involved in signal transduction. The N-terminal domain isolated from phyB, when dimerized and localized in the nucleus, triggered full phyB responses with much higher photosensitivity than the full-length phyB. These findings indicate that the C-terminal domain attenuates the activity of phyB rather than positively transducing the signal.
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Affiliation(s)
- Tomonao Matsushita
- Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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Sharrock RA, Clack T, Goosey L. Signaling activities among the Arabidopsis phyB/D/E-type phytochromes: a major role for the central region of the apoprotein. Plant J 2003; 34:317-326. [PMID: 12713538 DOI: 10.1046/j.1365-313x.2003.01722.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The Arabidopsis phyB, phyD, and phyE phytochromes regulate plant developmental and growth responses to continuous red light (R) and to the ratio of R to far-red (FR) light. The activities of these three photoreceptors in the control of seedling growth have been compared using a transgenic assay based upon induction of R-hypersensitivity of hypocotyl elongation by overexpression of the apoproteins from the 35S promoter. 35S-phyB, 35S-phyD, and 35S-phyE lines expressing similar levels of the respective phytochromes were isolated. Under pulses of R, phyB is very active in inducing a dwarf hypocotyl phenotype, whereas phyD and phyE are inactive. Under high-fluence continuous R, phyD shows a gain in activity whereas phyE does not. These results demonstrate significant differences in the inherent regulatory activities of these receptor apoproteins. To localize the sequence determinants of these functional differences, chimeric proteins were constructed by shuffling amino-terminal, central, and carboxy-terminal regions of phyB and phyD. Overexpression analysis of the phyB/D chimeras shows that it is the central region of these proteins that is most critical in determining their respective activities.
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Affiliation(s)
- Robert A Sharrock
- Department of Plant Sciences and Plant Pathology, Montana State University, Bozeman 59717, USA.
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Weller JL, Beauchamp N, Kerckhoffs LH, Platten JD, Reid JB. Interaction of phytochromes A and B in the control of de-etiolation and flowering in pea. Plant J 2001; 26:283-94. [PMID: 11439117 DOI: 10.1046/j.1365-313x.2001.01027.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The interactions of phytochrome A (phyA) and phytochrome B (phyB) in the photocontrol of vegetative and reproductive development in pea have been investigated using null mutants for each phytochrome. White-light-grown phyA phyB double mutant plants show severely impaired de-etiolation both at the seedling stage and later in development, with a reduced rate of leaf production and swollen, twisted internodes, and enlarged cells in all stem tissues. PhyA and phyB act in a highly redundant manner to control de-etiolation under continuous, high-irradiance red light. The phyA phyB double mutant shows no significant residual phytochrome responses for either de-etiolation or shade-avoidance, but undergoes partial de-etiolation in blue light. PhyB is shown to inhibit flowering under both long and short photoperiods and this inhibition is required for expression of the promotive effect of phyA. PhyA is solely responsible for the promotion of flowering by night-breaks with white light, whereas phyB appears to play a major role in detection of light quality in end-of-day light treatments, night breaks and day extensions. Finally, the inhibitory effect of phyB is not graft-transmissible, suggesting that phyB acts in a different manner and after phyA in the control of flower induction.
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Affiliation(s)
- J L Weller
- School of Plant Science, University of Tasmania, GPO Box 252-55 Hobart, Tasmania 7001, Australia.
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42
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Abstract
The family of phytochrome photoreceptors plays an essential role in regulating plant growth and development in response to the light environment. An antisense PHYB transgene has been introduced into wild-type Arabidopsis and shown to inhibit expression of the PHYB sense mRNA and the phyB phytochrome protein 4- to 5-fold. This inhibition is specific to phyB in that the levels of the four other phytochromes, notably the closely related phyD and phyE phytochromes, are unaffected in the antisense lines. Antisense-induced reduction in phyB causes alterations of red light effects on seedling hypocotyl elongation, rosette leaf morphology, and chlorophyll content, similar to the phenotypic changes caused by phyB null mutations. However, unlike the phyB mutants, the antisense lines do not flower early compared to the wild type. Furthermore, unlike the phyB mutants, the antisense lines do not show a reduction in phyC level compared to the wild type, making it possible to unequivocally associate several of the photomorphogenic effects seen in phyB mutants with phytochrome B alone. These results indicate that an antisense transgene approach can be used to specifically inhibit the expression and activity of a single member of the phytochrome family and to alter aspects of shade avoidance responses in a targeted manner.
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Affiliation(s)
- L Palecanda
- Department of Plant Sciences, Montana State University, Bozeman 59717, USA
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43
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Hennig L, Poppe C, Sweere U, Martin A, Schäfer E. Negative interference of endogenous phytochrome B with phytochrome A function in Arabidopsis. Plant Physiol 2001; 125:1036-44. [PMID: 11161059 PMCID: PMC64903 DOI: 10.1104/pp.125.2.1036] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2000] [Revised: 10/05/2000] [Accepted: 11/09/2000] [Indexed: 05/18/2023]
Abstract
To study negative interactions between phytochromes, phytochrome B (phyB) overexpressor lines, the mutants phyA-201, phyB-4, phyB-5, phyD-1, phyA-201 phyB-5, phyA-201 phyD-1, and phyB-5 phyD-1 of Arabidopsis were used. Endogenous phyB, but not phytochrome D (phyD), partly suppressed phytochrome A (phyA)-dependent inhibition of hypocotyl elongation in far-red light (FR). Dichromatic irradiation demonstrated that the negative effect of phyB was largely independent of the photoequilibrium, i.e. far-red light absorbing form of phytochrome formation. Moreover, phyB-4, a mutant impaired in signal transduction, did not show a loss of inhibition of phyA by phyB. Overexpression of phyB, conversely, resulted in an enhanced inhibition of phyA function, even in the absence of supplementary carbohydrates. However, overexpression of a mutated phyB, which cannot incorporate the chromophore, had no detectable effect on phyA action. In addition to seedling growth, accumulation of anthocyanins in FR, another manifestation of the high irradiance response, was strongly influenced by phyB holoprotein. Induction of seed germination by FR, a very low fluence response, was suppressed by both endogenous phyB and phyD. In conclusion, we show that both classical response modes of phyA, high irradiance response, and very low fluence response are subject to an inhibitory action of phyB-like phytochromes. Possible mechanisms of the negative interference are discussed.
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Affiliation(s)
- L Hennig
- Institut für Biologie II, Universität Freiburg, Schänzlestrasse 1, 79104 Freiburg, Germany
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Zhu Y, Tepperman JM, Fairchild CD, Quail PH. Phytochrome B binds with greater apparent affinity than phytochrome A to the basic helix-loop-helix factor PIF3 in a reaction requiring the PAS domain of PIF3. Proc Natl Acad Sci U S A 2000; 97:13419-24. [PMID: 11069292 PMCID: PMC27239 DOI: 10.1073/pnas.230433797] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The signaling pathways by which the phytochrome (phy) family of photoreceptors transmits sensory information to light-regulated genes remain to be fully defined. Evidence for a relatively direct pathway has been provided by the binding of one member of the family, phyB, to a promoter-element-bound, basic helix-loop-helix protein, PIF3, specifically upon light-induced conversion of the photoreceptor molecule to its biologically active conformer (Pfr). Here, we show that phyA also binds selectively and reversibly to PIF3 upon photoconversion to Pfr, but that the apparent affinity of PIF3 for phyA is 10-fold lower than for phyB. This result is consistent with previous in vivo data from PIF3-deficient Arabidopsis, indicating that PIF3 has a major role in phyB signaling, but a more minor role in phyA signaling. We also show that phyB binds stoichiometrically to PIF3 at an equimolar ratio, suggesting that the resultant complex is the unit active in transcriptional regulation at target promoters. Deletion mapping suggests that a 37-aa segment present at the N terminus of phyB, but absent from phyA, contributes strongly to the high binding affinity of phyB for PIF3. Conversely, deletion mapping and point mutation analysis of PIF3 for determinants involved in recognition of phyB indicates that the PAS domain of PIF3 is a major contributor to this interaction, but that a second determinant in the C-terminal domain is also necessary.
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Affiliation(s)
- Y Zhu
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
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45
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Abstract
As part of an effort to isolate new Arabidopsis mutants specifically defective in responsiveness to red light, we identified srl1 (short hypocotyl in red light) by screening an EMS-mutagenized M2 population derived from a phytochrome B (phyB)-overexpressor line (ABO). The srl1 mutant shows enhanced responsiveness to continuous red but not far-red light, in both wild-type and ABO backgrounds, consistent with involvement in the phyB-signaling pathway but not that of phyA. The hypersensitive phenotype of srl1 is not due to overexpression of endogenous phyA or phyB, and the locus maps to the center of chromosome 2, distinct from any other known photomorphogenic mutants. srl1 seedlings display enhancement of several phyB-mediated responses, including shorter hypocotyls, more expanded cotyledons, shorter petioles and modestly higher levels of CAB gene expression under red light than the wild type. Double mutant analyses show that the hypersensitive phenotype of srl1 is completely phyB-dependent. The data suggest, therefore, that SRL1 may encode a negatively acting component specific to the phyB-signaling pathway.
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Affiliation(s)
- E Huq
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
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46
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Abstract
The plant receptor phytochrome A (phyA) mediates responses like hypocotyl growth inhibition and cotyledon unfolding that require continuous far-red (FR) light for maximum expression (high-irradiance responses, HIR), and responses like seed germination that can be induced by a single pulse of FR (very-low-fluence responses, VLFR). It is not known whether this duality results from either phyA interaction with different end-point processes or from the intrinsic properties of phyA activity. Etiolated seedlings of Arabidopsis thaliana were exposed to pulses of FR (3 min) separated by dark intervals of different duration. Hypocotyl-growth inhibition and cotyledon unfolding showed two phases. The first phase (VLFR) between 0.17 and 0.5 pulses.h-1, a plateau between 0.5 and 2 pulses.h-1 and a second phase (HIR) at higher frequencies. Reciprocity between fluence rate and duration of FR was observed within phases, not between phases. The fluence rate for half the maximum effect was 0.1 and 3 mumol.m-2.s-1 for hourly pulses of FR (VLFR) and continuous FR (HIR), respectively. Overexpression of phytochrome B caused dominant negative suppression under continuous but not under hourly FR. We conclude that phyA is intrinsically able to initiate two discrete photoresponses even when a single end-point process is considered.
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Affiliation(s)
- J J Casal
- IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, Argentina.
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47
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Casal JJ. Phytochromes, cryptochromes, phototropin: photoreceptor interactions in plants. Photochem Photobiol 2000. [PMID: 10649883 DOI: 10.1562/0031-8655(2000)071%3c0001:pcppii%3e2.0.co;2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
In higher plants, natural radiation simultaneously activates more than one photoreceptor. Five phytochromes (phyA through phyD), two cryptochromes (cry1, cry2) and phototropin have been identified in the model species Arabidopsis thaliana. There is light-dependent epistasis among certain photoreceptor genes because the action of one pigment can be affected by the activity of others. Under red light, phyA and phyB are antagonistic, but under far-red light, followed by brief red light, phyA and phyB are synergistic in the control of seedling morphology and the expression of some genes during de-etiolation. Under short photoperiods of red and blue light, cry1 and phyB are synergistic, but under continuous exposure to the same light field the actions of phyB and cry1 become independent and additive. Phototropic bending of the shoot toward unilateral blue light is mediated by phototropin, but cry1, cry2, phyA and phyB positively regulate the response. Finally, cry2 and phyB are antagonistic in the induction of flowering. At least some of these interactions are likely to result from cross talk of the photoreceptor signaling pathways and uncover new avenues to approach signal transduction. Experiments under natural radiation are beginning to show that the interactions create a phototransduction network with emergent properties. This provides a more robust system for light perception in plants.
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Affiliation(s)
- J J Casal
- IFEVA, Departamento de Ecología, Facultad de Agronomía, Universidad de Buenos Aires, Argentina.
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48
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Abstract
In higher plants, natural radiation simultaneously activates more than one photoreceptor. Five phytochromes (phyA through phyD), two cryptochromes (cry1, cry2) and phototropin have been identified in the model species Arabidopsis thaliana. There is light-dependent epistasis among certain photoreceptor genes because the action of one pigment can be affected by the activity of others. Under red light, phyA and phyB are antagonistic, but under far-red light, followed by brief red light, phyA and phyB are synergistic in the control of seedling morphology and the expression of some genes during de-etiolation. Under short photoperiods of red and blue light, cry1 and phyB are synergistic, but under continuous exposure to the same light field the actions of phyB and cry1 become independent and additive. Phototropic bending of the shoot toward unilateral blue light is mediated by phototropin, but cry1, cry2, phyA and phyB positively regulate the response. Finally, cry2 and phyB are antagonistic in the induction of flowering. At least some of these interactions are likely to result from cross talk of the photoreceptor signaling pathways and uncover new avenues to approach signal transduction. Experiments under natural radiation are beginning to show that the interactions create a phototransduction network with emergent properties. This provides a more robust system for light perception in plants.
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Affiliation(s)
- J J Casal
- IFEVA, Departamento de Ecología, Facultad de Agronomía, Universidad de Buenos Aires, Argentina.
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49
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Affiliation(s)
- H Linden
- Lehrstuhl fur Physiologie und Biochemie der Pflanzen Universitat Konstanz, Germany
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50
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Halliday KJ, Hudson M, Ni M, Qin M, Quail PH. poc1: an Arabidopsis mutant perturbed in phytochrome signaling because of a T DNA insertion in the promoter of PIF3, a gene encoding a phytochrome-interacting bHLH protein. Proc Natl Acad Sci U S A 1999; 96:5832-7. [PMID: 10318970 PMCID: PMC21946 DOI: 10.1073/pnas.96.10.5832] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The phytochrome family of informational photoreceptors has a central role in regulating light-responsive gene expression, but the mechanism of intracellular signal transduction has remained elusive. In a genetic screen for T DNA-tagged Arabidopsis mutants affected in early signaling intermediates, we identified poc1 (photocurrent 1), which exhibits enhanced responsiveness to red light. This phenotype is absent in a phyB (phytochrome B) null mutant background, indicating that the poc1 mutation enhances phyB signal transduction. The T DNA insertion in poc1 was found to be located in the promoter region of PIF3, a gene encoding a basic helix-loop-helix protein. The mutant phenotype seems to result from insertion-induced overexpression of this gene in red-light-grown seedlings, consistent with PIF3 functioning as a positively acting signaling intermediate. These findings, combined with data from a separate yeast two-hybrid screen that identified PIF3 as a phytochrome-interacting factor necessary for normal signaling, provide evidence that phytochrome signal transduction may include a direct pathway to photoresponsive nuclear genes via physical interaction of the photoreceptor molecules with the potential transcriptional regulator PIF3.
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Affiliation(s)
- K J Halliday
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
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