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Patharkar OR, Walker JC. Connections between abscission, dehiscence, pathogen defense, drought tolerance, and senescence. Plant Science 2019; 284:25-29. [PMID: 31084875 DOI: 10.1016/j.plantsci.2019.03.016] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 02/12/2019] [Accepted: 03/20/2019] [Indexed: 05/22/2023]
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Abstract
Abscission is a process in plants for shedding unwanted organs such as leaves, flowers, fruits, or floral organs. Shedding of leaves in the fall is the most visually obvious display of abscission in nature. The very shape plants take is forged by the processes of growth and abscission. Mankind manipulates abscission in modern agriculture to do things such as prevent pre-harvest fruit drop prior to mechanical harvesting in orchards. Abscission occurs specifically at abscission zones that are laid down as the organ that will one day abscise is developed. A sophisticated signaling network initiates abscission when it is time to shed the unwanted organ. In this article, we review recent advances in understanding the signaling mechanisms that activate abscission. Physiological advances and roles for hormones in abscission are also addressed. Finally, we discuss current avenues for basic abscission research and potentially lucrative future directions for its application to modern agriculture.
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Affiliation(s)
- O Rahul Patharkar
- Division of Biological Sciences and Interdisciplinary Plant Group, University of Missouri, Columbia, MO, USA
| | - John C Walker
- Division of Biological Sciences and Interdisciplinary Plant Group, University of Missouri, Columbia, MO, USA
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Patharkar OR, Gassmann W, Walker JC. Leaf shedding as an anti-bacterial defense in Arabidopsis cauline leaves. PLoS Genet 2017; 13:e1007132. [PMID: 29253890 PMCID: PMC5749873 DOI: 10.1371/journal.pgen.1007132] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 01/02/2018] [Accepted: 11/28/2017] [Indexed: 01/04/2023] Open
Abstract
Plants utilize an innate immune system to protect themselves from disease. While many molecular components of plant innate immunity resemble the innate immunity of animals, plants also have evolved a number of truly unique defense mechanisms, particularly at the physiological level. Plant's flexible developmental program allows them the unique ability to simply produce new organs as needed, affording them the ability to replace damaged organs. Here we develop a system to study pathogen-triggered leaf abscission in Arabidopsis. Cauline leaves infected with the bacterial pathogen Pseudomonas syringae abscise as part of the defense mechanism. Pseudomonas syringae lacking a functional type III secretion system fail to elicit an abscission response, suggesting that the abscission response is a novel form of immunity triggered by effectors. HAESA/HAESA-like 2, INFLORESCENCE DEFICIENT IN ABSCISSION, and NEVERSHED are all required for pathogen-triggered abscission to occur. Additionally phytoalexin deficient 4, enhanced disease susceptibility 1, salicylic acid induction-deficient 2, and senescence-associated gene 101 plants with mutations in genes necessary for bacterial defense and salicylic acid signaling, and NahG transgenic plants with low levels of salicylic acid fail to abscise cauline leaves normally. Bacteria that physically contact abscission zones trigger a strong abscission response; however, long-distance signals are also sent from distal infected tissue to the abscission zone, alerting the abscission zone of looming danger. We propose a threshold model regulating cauline leaf defense where minor infections are handled by limiting bacterial growth, but when an infection is deemed out of control, cauline leaves are shed. Together with previous results, our findings suggest that salicylic acid may regulate both pathogen- and drought-triggered leaf abscission.
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Affiliation(s)
- O. Rahul Patharkar
- Division of Biological Sciences and Interdisciplinary Plant Group, University of Missouri, Columbia, MO, United States of America
| | - Walter Gassmann
- Division of Plant Sciences, CS Bond Life Sciences Center and Interdisciplinary Plant Group, University of Missouri, Columbia, MO, United States of America
| | - John C. Walker
- Division of Biological Sciences and Interdisciplinary Plant Group, University of Missouri, Columbia, MO, United States of America
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Patharkar OR, Walker JC. Core Mechanisms Regulating Developmentally Timed and Environmentally Triggered Abscission. Plant Physiol 2016; 172:510-20. [PMID: 27468996 PMCID: PMC5074626 DOI: 10.1104/pp.16.01004] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 07/27/2016] [Indexed: 05/21/2023]
Abstract
Drought-triggered abscission is a strategy used by plants to avoid the full consequences of drought; however, it is poorly understood at the molecular genetic level. Here, we show that Arabidopsis (Arabidopsis thaliana) can be used to elucidate the pathway controlling drought-triggered leaf shedding. We further show that much of the pathway regulating developmentally timed floral organ abscission is conserved in regulating drought-triggered leaf abscission. Gene expression of HAESA (HAE) and INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) is induced in cauline leaf abscission zones when the leaves become wilted in response to limited water and HAE continues to accumulate in the leaf abscission zones through the abscission process. The genes that encode HAE/HAESA-LIKE2, IDA, NEVERSHED, and MAPK KINASE4 and 5 are all necessary for drought-induced leaf abscission. Our findings offer a molecular mechanism explaining drought-triggered leaf abscission. Furthermore, the ability to study leaf abscission in Arabidopsis opens up a new avenue to tease apart mechanisms involved in abscission that have been difficult to separate from flower development as well as for understanding the mechanistic role of water and turgor pressure in abscission.
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Affiliation(s)
- O Rahul Patharkar
- Division of Biological Sciences and Interdisciplinary Plant Group, University of Missouri, Columbia, Missouri 65211
| | - John C Walker
- Division of Biological Sciences and Interdisciplinary Plant Group, University of Missouri, Columbia, Missouri 65211
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Niederhuth CE, Patharkar OR, Walker JC. Transcriptional profiling of the Arabidopsis abscission mutant hae hsl2 by RNA-Seq. BMC Genomics 2013; 14:37. [PMID: 23327667 PMCID: PMC3566969 DOI: 10.1186/1471-2164-14-37] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Accepted: 01/14/2013] [Indexed: 01/20/2023] Open
Abstract
BACKGROUND Abscission is a mechanism by which plants shed entire organs in response to both developmental and environmental signals. Arabidopsis thaliana, in which only the floral organs abscise, has been used extensively to study the genetic, molecular and cellular processes controlling abscission. Abscission in Arabidopsis requires two genes that encode functionally redundant receptor-like protein kinases, HAESA (HAE) and HAESA-LIKE 2 (HSL2). Double hae hsl2 mutant plants fail to abscise their floral organs at any stage of floral development and maturation. RESULTS Using RNA-Seq, we compare the transcriptomes of wild-type and hae hsl2 stage 15 flowers, using the floral receptacle which is enriched for abscission zone cells. 2034 genes were differentially expressed with a False Discovery Rate adjusted p < 0.05, of which 349 had two fold or greater change in expression. Differentially expressed genes were enriched for hydrolytic, cell wall modifying, and defense related genes. Testing several of the differentially expressed genes in INFLORESCENCE DEFICIENT IN ABSCISSION (ida) mutants shows that many of the same genes are co-regulated by IDA and HAE HSL2 and support the role of IDA in the HAE and HSL2 signaling pathway. Comparison to microarray data from stamen abscission zones show distinct patterns of expression of genes that are dependent on HAE HSL2 and reveal HAE HSL2- independent pathways. CONCLUSION HAE HSL2-dependent and HAE HSL2-independent changes in genes expression are required for abscission. HAE and HSL2 affect the expression of cell wall modifying and defense related genes necessary for abscission. The HAE HSL2-independent genes also appear to have roles in abscission and additionally are involved in processes such as hormonal signaling, senescence and callose deposition.
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Affiliation(s)
- Chad E Niederhuth
- Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA
- Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211, USA
- Interdisciplinary Plant Group, University of Missouri, Columbia, Missouri 65211, USA
| | - O Rahul Patharkar
- Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA
- Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211, USA
- Interdisciplinary Plant Group, University of Missouri, Columbia, Missouri 65211, USA
| | - John C Walker
- Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA
- Bond Life Sciences Center, University of Missouri, Columbia, Missouri 65211, USA
- Interdisciplinary Plant Group, University of Missouri, Columbia, Missouri 65211, USA
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Chehab EW, Patharkar OR, Cushman JC. Isolation and characterization of a novel v-SNARE family protein that interacts with a calcium-dependent protein kinase from the common ice plant, Mesembryanthemum crystallinum. Planta 2007; 225:783-99. [PMID: 16947054 DOI: 10.1007/s00425-006-0371-4] [Citation(s) in RCA: 6] [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: 04/17/2006] [Revised: 08/01/2006] [Accepted: 08/02/2006] [Indexed: 05/11/2023]
Abstract
McCPK1 (Mesembryanthemum crystallinum calcium-dependent protein kinase 1) mRNA expression is transiently salinity- and dehydrationstress responsive. The enzyme also undergoes dynamic subcellular localization changes in response to these same stresses. Using the yeast-two hybrid system, we have isolated and characterized a M. crystallinum CPK1 Adaptor Protein 2 (McCAP2). We show that McCPK1 interacts with the C-terminal, coiled-coil containing region of McCAP2 in the yeast two-hybrid system. This interaction was confirmed in vitro between the purified recombinant forms of each of the proteins and in vivo by coimmunoprecipitation experiments from plant extracts. McCAP2, however, was not a substrate for McCPK1. Computational threading analysis suggested that McCAP2 is a member of a novel family of proteins with unknown function also found in rice and Arabidopsis. These proteins contain coiled-coil spectrin repeat domains present in the syntaxin super-family that participate in vesicular and protein trafficking. Consistent with the interaction data, subcellular localization and fractionation studies showed that McCAP2 colocalizes with McCPK1 to vesicular structures located on the actin cytoskeleton and within the endoplasmic reticulum in cells subjected to low humidity stress. McCAP2 also colocalizes with AtVTIl1a, an Arabidopsis v-SNARE [vesicle-soluble N-ethyl maleimide-sensitive factor (NSF) attachment protein (SNAP) receptor] present in the trans-Golgi network (TGN) and prevacuolar compartments (PVCs). Both interaction and subcellular localization studies suggest that McCAP2 may possibly serve as an adaptor protein responsible for vesicle-mediated trafficking of McCPK1 to or from the plasma membrane along actin microfilaments of the cytoskeleton.
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Affiliation(s)
- E Wassim Chehab
- Department of Biochemistry and Molecular Biology/MS200, 311 Fleischmann Agriculture, University of Nevada, Reno, NV 89557-0014, USA
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Patharkar OR, Cushman JC. A novel coiled-coil protein co-localizes and interacts with a calcium-dependent protein kinase in the common ice plant during low-humidity stress. Planta 2006; 225:57-73. [PMID: 16773372 DOI: 10.1007/s00425-006-0330-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2006] [Accepted: 05/20/2006] [Indexed: 05/10/2023]
Abstract
McCPK1 (Mesembryanthemum crystallinum calcium-dependent protein kinase 1) mRNA expression is induced transiently by salinity and water deficit stress and also McCPK1 undergoes dynamic subcellular localization changes in response to these same stresses. Here we have confirmed that low humidity is capable of causing a drastic change in McCPK1's subcellular localization. We attempted to elucidate this phenomenon by isolating components likely to be involved in this process. McCAP1 (M. crystallinum CDPK adapter protein 1) was cloned in a yeast two-hybrid screen with a constitutively active McCPK1 as bait. We show that McCPK1 and McCAP1 can interact in the yeast two-hybrid system, in vitro, and in vivo as demonstrated by coimmunoprecipitation experiments from plant extracts. However, McCAP1 does not appear to be a substrate for McCPK1. DsRed-McCAP1 and EGFP-McCPK1 fusions colocalize in epidermal cells of ice plants exposed to low humidity. McCAP1 is homologous to a family of proteins in Arabidopsis with no known function. Computational threading analysis suggests that McCAP1 is likely to be an intermediate filament protein of the cytoskeleton.
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Affiliation(s)
- O Rahul Patharkar
- Department of Molecular Biology, Massachusetts General Hospital, Wellman 11, Boston, MA 02114, USA
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Chehab EW, Patharkar OR, Hegeman AD, Taybi T, Cushman JC. Autophosphorylation and subcellular localization dynamics of a salt- and water deficit-induced calcium-dependent protein kinase from ice plant. Plant Physiol 2004; 135:1430-46. [PMID: 15247393 PMCID: PMC519060 DOI: 10.1104/pp.103.035238] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2003] [Revised: 04/19/2004] [Accepted: 04/26/2004] [Indexed: 05/18/2023]
Abstract
A salinity and dehydration stress-responsive calcium-dependent protein kinase (CDPK) was isolated from the common ice plant (Mesembryanthemum crystallinum; McCPK1). McCPK1 undergoes myristoylation, but not palmitoylation in vitro. Removal of the N-terminal myristate acceptor site partially reduced McCPK1 plasma membrane (PM) localization as determined by transient expression of green fluorescent protein fusions in microprojectile-bombarded cells. Removal of the N-terminal domain (amino acids 1-70) completely abolished PM localization, suggesting that myristoylation and possibly the N-terminal domain contribute to membrane association of the kinase. The recombinant, Escherichia coli-expressed, full-length McCPK1 protein was catalytically active in a calcium-dependent manner (K0.5 = 0.15 microm). Autophosphorylation of recombinant McCPK1 was observed in vitro on at least two different Ser residues, with the location of two sites being mapped to Ser-62 and Ser-420. An Ala substitution at the Ser-62 or Ser-420 autophosphorylation site resulted in a slight increase in kinase activity relative to wild-type McCPK1 against a histone H1 substrate. In contrast, Ala substitutions at both sites resulted in a dramatic decrease in kinase activity relative to wild-type McCPK1 using histone H1 as substrate. McCPK1 undergoes a reversible change in subcellular localization from the PM to the nucleus, endoplasmic reticulum, and actin microfilaments of the cytoskeleton in response to reductions in humidity, as determined by transient expression of McCPK1-green fluorescent protein fusions in microprojectile-bombarded cells and confirmed by subcellular fractionation and western-blot analysis of 6x His-tagged McCPK1.
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Affiliation(s)
- E Wassim Chehab
- Department of Biochemistry/MS200, University of Nevada, Reno, Nevada 89557-0014, USA
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Patharkar OR, Cushman JC. A stress-induced calcium-dependent protein kinase from Mesembryanthemum crystallinum phosphorylates a two-component pseudo-response regulator. Plant J 2000; 24:679-91. [PMID: 11123806 DOI: 10.1046/j.1365-313x.2000.00912.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
McCDPK1 is a salinity- and drought-induced calcium-dependent protein kinase (CDPK) isolated from the common ice plant, Mesembryanthemum crystallinum. A yeast two-hybrid experiment was performed, using full-length McCDPK1 and truncated forms of McCDPK1 as baits, to identify interacting proteins. A catalytically impaired bait isolated a cDNA clone encoding a novel protein, CDPK substrate protein 1 (CSP1). CSP1 interacted with McCDPK1 in a substrate-like fashion in both yeast two-hybrid assays and wheat germ interaction assays. Furthermore, McCDPK1 was capable of phosphorylating CSP1 in vitro in a calcium-dependent manner. Our results demonstrate that the use of catalytically impaired and unregulated CDPKs with the yeast two-hybrid system can accelerate the discovery of CDPK substrates. The deduced CSP1 amino acid sequence indicated that it is a novel member of a class of pseudo-response regulator-like proteins that have a highly conserved helix-loop-helix DNA binding domain and a C-terminal activation domain. McCDPK1 and CSP1 co-localized to nuclei of NaCl-stressed ice plants. Csp1 transcript accumulation was not regulated by NaCl or dehydration stress. Our results strongly suggest that McCDPK1 may regulate the function of CSP1 by reversible phosphorylation.
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Affiliation(s)
- O R Patharkar
- Department of Biochemistry/MS200, 311B Fleischmann Agriculture, University of Nevada, Reno, NV 89557-0014, USA
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