Arabidopsis membrane steroid binding protein 1 is involved in inhibition of cell elongation

Pregnane derivatives in wheat (Triticum aestivum) and their potential role in generative development

Pregnane derivatives such as pregnenolone or progesterone and many other metabolites are important in mammals where many of them act as hormones including sexual hormones. Much less is known about the presence and functions of pregnane derivatives in plants. The main objectives of this work were (1) to determine the presence of pregnane derivatives in winter wheat (2) verify if there are changes of concentration of pregnane derivatives during wheat growth/development with special attention to vernalisation process (3) to answer the question of whether selected pregnane derivatives are stimulators of wheat development and whether the potential stimulation of this development is accompanied by the expression of the Vrn1 (Vernalisation1) gene. To the best of our knowledge, this is the first report that demonstrates the presence of pregnenolone and 5α-dihydroprogesterone in the leaves and intact crowns of winter wheat. The levels of some of the pregnane derivatives changed during plant growth/development, it was demonstrated that pregnenolone, pregnanolone and 17α-hydroxypregnenolone stimulated wheat development. The changes in the Vrn1 expression are discussed in light of the stimulation of generative development by the pregnane derivatives.

Genome-wide association study dissects the genetic architecture of progesterone content in Persian walnut leaves (Juglans regia L.)

Progesterone (P4) is an endogenous sex steroid hormone involved in the ovulatory cycle and pregnancy of animal species. In sheep and goats, P4 analogues are used to induce synchronized ovulations and oestrus behavior of the females. In humans, P4 from chemical synthesis is used to treat peri-menopausal disorders. However, such molecules are released into aquatic environment and can be a source of pollution, are prohibited in organic farms and go against the trend of "naturality" in animal production as well as in human health. A natural alternative may consist in the extraction and use of P4 in plants. Mammalian hormones were discovered in an increasing number of plant species, including walnut leaves that contain high levels of P4. We compared the content of P4 in leaves of 170 accessions of Juglans regia from the walnut germplasm collection of INRAE Prunus-Juglans Biological Resources Center previously genotyped using the Axiom™ J. regia 700 K SNP array. We conducted a genome-wide association study (GWAS) using multi-locus models. When collected in October, P4 content goes from 34,1 to 287,5 mg/kg dry weight of leaves. The two laciniate accessions have the largest P4 content. We identified seven significant marker-trait associations on chromosomes 1, 2, 3, 6, 7, 15 and 16, and a candidate gene involved in the metabolism of sterols, precursors of plant steroid hormones. Our results raise the huge variability of P4 content within J. regia and propose a candidate gene which may have a role in the control of this variability, opening the way to a potential use of walnut P4 by the pharmaceutical industry towards more natural source of chemical compounds.

Occurrence and conversion of progestogens and androgens are conserved in land plants

Progestogens and androgens have been found in many plants, but little is known about their biosynthesis and the evolution of steroidogenesis in these organisms. Here, we show that the occurrence and biosynthesis of progestogens and androgens are conserved across the viridiplantae lineage. An UHPLC-ESI-MS/MS method allowed high-throughput analysis of the occurrence and chemical conversion of progestogens and androgens in 41 species across the green plant lineage. Dehydroepiandrosterone, testosterone, and 5α-dihydrotestosterone are plants' most abundant mammalian-like steroids. Progestogens are converted into 17α-hydroxyprogesterone and 5α-pregnane-3,20-dione. Androgens are converted into testosterone and 5α-dihydrotestosterone. 17,20-Lyases, essential for converting progestogens to androgens, seem to be most effective in monocot species. Our data suggest that the occurrence of progestogens and androgens is highly conserved in plants, and their biosynthesis might favor a route using the Δ4 pathway.

The Role of Plant Progesterone in Regulating Growth, Development, and Biotic/Abiotic Stress Responses

Progesterone is a steroid hormone that performs important functions in mammals. However, studies on its physiological functions in plants have gradually increased in recent years. Therefore, this review summarizes the regulatory functions of progesterone on plant growth and development, as well as its response to stress. Moreover, the plant metabolic processes of progesterone are also discussed. Overall, progesterone is ubiquitous in plants and can regulate numerous plant physiological processes at low concentrations. Since progesterone shares similar characteristics with plant hormones, it is expected to become a candidate for plant hormone. However, most of the current research on progesterone in plants is limited to the physiological level, and more molecular level research is needed to clarify progesterone signaling pathways.

Physiological, Proteomic Analysis, and Calcium-Related Gene Expression Reveal Taxus wallichiana var. mairei Adaptability to Acid Rain Stress Under Various Calcium Levels

As one of the serious environmental problems worldwide, acid rain (AR) has always caused continuous damage to the forestry ecosystem. Studies have shown that AR can leach calcium ions from plants and soil. Calcium (Ca) is also a crucial regulator of the plant stress response, whereas there are few reports on how Ca regulates the response of AR-resistant woody plants to AR stress. In this study, by setting different exogenous Ca levels, we study the physiological and molecular mechanism of Ca in regulating the Taxus wallichiana var. mairei response to AR stress. Our results showed that low Ca level leads to photosynthesis, and antioxidant defense system decreases in T. wallichiana var. mairei leaves; however, these negative effects could be reversed at high Ca level. In addition, proteomic analyses identified 44 differentially expressed proteins in different Ca level treatments of T. wallichiana var. mairei under AR stress. These proteins were classified into seven groups, which include metabolic process, photosynthesis and energy pathway, cell rescue and defense, transcription and translation, protein modification and degradation, signal transduction, etc. Furthermore, the study found that low Ca level leads to an obvious increase of Ca-related gene expression under AR stress in T. wallichiana var. mairei using qRT-PCR analyses and however can be reversed at high Ca level. These findings would enrich and extend the Ca signaling pathways of AR stress in AR-resistant woody plants and are expected to have important theoretical and practical significance in revealing the mechanism of woody plants tolerating AR stress and protecting forestry ecosystem in soil environment under different Ca levels.

ATI1 (ATG8-interacting protein 1) and ATI2 define a plant starvation-induced reticulophagy pathway and serve as MSBP1/MAPR5 cargo receptors

Reticulophagy, the selective autophagy of endoplasmic reticulum (ER) components, is known to operate in eukaryotes from yeast and unicellular algae to animals and plants. Thus far, only ER-stress induced reticulophagy was reported and analyzed in plants. In this study we characterize a reticulophagy pathway in Arabidopsis thaliana that is triggered by dark-induced starvation but not by ER stress. This pathway is defined by the previously reported ATG8-interacting proteins, ATI1 and ATI2. We further identified the ER-localized MSBP1 (Membrane Steroid Binding Protein 1) as an ATI1- and ATI2-interacting protein and an autophagy cargo, and show that ATI1 and ATI2 serve as its cargo receptors. Together, these findings expand our knowledge on plant responses during energy deprivation and highlight the role of this special type of reticulophagy in this process.Abbreviations: AGO1: ARGONAUTE 1; ATI: ATG8-Interacting Protein; BiFC: Bimolecular Fluorescence Complementation; BR: brassinosteroid; conA: concanamycin A; DMSO: dimethyl sulfoxid; DTT: dithiothreitol; ER: endoplasmic reticulum; GFP: green fluorescent protein; MAPR: Membrane-Associated Progesterone Binding Protein; MSBP: Membrane Steroid Binding Protein; SD: standard deviation; SE: standard error; TM: tunicamycin; TOR: target of rapamycin; Y2H: yeast two-hybrid.

Comparative proteomic analysis reveals that the Heterosis of two maize hybrids is related to enhancement of stress response and photosynthesis respectively

BACKGROUND

Heterosis refers to superior traits exhibiting in a hybrid when compared with both parents. Generally, the hybridization between parents can change the expression pattern of some proteins such as non-additive proteins (NAPs) which might lead to heterosis. 'Zhongdan808' (ZD808) and 'Zhongdan909' (ZD909) are excellent maize hybrids in China, however, the heterosis mechanism of them are not clear. Proteomics has been wildly used in many filed, and comparative proteomic analysis of hybrid and its parents is helpful for understanding the mechanism of heterosis in the two maize hybrids.

RESULTS

Over 2000 protein groups were quantitatively identified from second seedling leaves of two hybrids and their parents by label-free quantification. Statistical analysis of total identified proteins, differentially accumulated proteins (DAPs) and NAPs of the two hybrids revealed that both of them were more similar to their female parents. In addition, most of DAPs were up-regulated and most of NAPs were high parent abundance or above-high parent abundance in ZD808, while in ZD909, most of DAPs were down-regulated and most of NAPs were low parent abundance or below-low parent abundance. Pathway enrichment analysis showed that more of stress response-related NAPs in ZD808 were high parent abundance or above-high parent abundance, and most of PS related NAPs in ZD909 were high parent abundance or above-high parent abundance. Finally, four stress response-related proteins and eight proteins related to PS were verified by PRM, ten of them had significant differences between hybrid and midparent value.

CONCLUSIONS

Even though every one of the two hybrids were more similar to its female parent at proteome level, the biological basis of heterosis is different in the two maize hybrids. In comparison with their parents, the excellent agronomic traits of hybrid ZD808 is mainly correlated with the high expression levels of some proteins related to stress responses and metabolic functions, while traits of ZD909 is mainly correlated with high expressed proteins related to photosynthesis. Our proteomics results support previous physiological and morphological research and have provided useful information in understanding the reason of valuable agronomic traits.

Brassinosteroid-Activated BRI1-EMS-SUPPRESSOR 1 Inhibits Flavonoid Biosynthesis and Coordinates Growth and UV-B Stress Responses in Plants

UV-B light is a potential stress factor in plants, but how plants coordinate growth and UV-B stress responses is not well understood. Here, we report that brassinosteroid (BR) signaling inhibits UV-B stress responses in Arabidopsis (Arabidopsis thaliana) and various crops by controlling flavonol biosynthesis. We further demonstrate that BRI1-EMS-SUPPRESSOR 1 (BES1) mediates the tradeoff between plant growth and UV-B defense responses. BES1, a master transcription factor involved in BR signaling, represses the expression of transcription factor genes MYB11, MYB12, and MYB111, which activate flavonol biosynthesis. BES1 directly binds to the promoters of these MYBs in a BR-enhanced manner to repress their expression, thereby reducing flavonol accumulation. However, exposure to broadband UV-B down-regulates BES1 expression, thus promoting flavonol accumulation. These findings demonstrate that BR-activated BES1 not only promotes growth but also inhibits flavonoid biosynthesis. UV-B stress suppresses the expression of BES1 to allocate energy to flavonoid biosynthesis and UV-B stress responses, allowing plants to switch from growth to UV-B stress responses in a timely manner.

Global profiling of plant nuclear membrane proteome in Arabidopsis

The nuclear envelope (NE) is structurally and functionally vital for eukaryotic cells, yet its protein constituents and their functions are poorly understood in plants. Here, we combined subtractive proteomics and proximity-labelling technology coupled with quantitative mass spectrometry to understand the landscape of NE membrane proteins in Arabidopsis. We identified ~200 potential candidates for plant NE transmembrane (PNET) proteins, which unravelled the compositional diversity and uniqueness of the plant NE. One of the candidates, named PNET1, is a homologue of human TMEM209, a critical driver for lung cancer. A functional investigation revealed that PNET1 is a bona fide nucleoporin in plants. It displays both physical and genetic interactions with the nuclear pore complex (NPC) and is essential for embryo development and reproduction in different NPC contexts. Our study substantially enlarges the plant NE proteome and sheds new light on the membrane composition and function of the NPC.

A Bridge to the World

Zhi-Hong Xu is a plant physiologist who studied botany at Peking University (1959–1965). He joined the Shanghai Institute of Plant Physiology (SIPP), Chinese Academy of Sciences (CAS), as a graduate student in 1965. He recalls what has happened for the institute, during the Cultural Revolution, and he witnessed the spring of science eventually coming to China. Xu was a visiting scholar at the John Innes Institute and in the Department of Botany at Nottingham University in the United Kingdom (1979–1981). He became deputy director of SIPP in 1983 and director in 1991; he also chaired the State Key Laboratory of Plant Molecular Genetics SIPP (1988–1996). He worked as a visiting scientist in the Institute of Molecular and Cell Biology, National University of Singapore, for three months each year (1989–1992). He served as vice president of CAS (1992–2002) and as president of Peking University (1999–2008). Over these periods he was heavily involved in the design and implementation of major scientific projects in life sciences and agriculture in China. He is an academician of CAS and member of the Academy of Sciences for the Developing World. His scientific contributions mainly cover plant tissue culture, hormone mechanism in development, as well as plant developmental response to environment. Xu, as a scientist and leader who has made an impact in the community, called up a lot of excellent young scientists returning to China. His efforts have promoted the fast development of China's plant and agricultural sciences.

Whole-Transcriptome Analysis Unveils the Synchronized Activities of Genes for Fructans in Developing Tubers of the Jerusalem Artichoke

Helianthus tuberosus L., known as the Jerusalem artichoke, is a hexaploid plant species, adapted to low-nutrient soils, that accumulates high levels of inulin in its tubers. Inulin is a fructose-based polysaccharide used either as dietary fiber or for the production of bioethanol. Key enzymes involved in inulin biosynthesis are well known. However, the gene networks underpinning tuber development and inulin accumulation in H. tuberous remain elusive. To fill this gap, we selected 6,365 expressed sequence tags (ESTs) from an H. tuberosus library to set up a microarray platform and record their expression across three tuber developmental stages, when rhizomes start enlarging (T0), at maximum tuber elongation rate (T3), and at tuber physiological maturity (Tm), in "VR" and "K8-HS142"clones. The former was selected as an early tuberizing and the latter as a late-tuberizing clone. We quantified inulin and starch levels, and qRT-PCR confirmed the expression of critical genes accounting for inulin biosynthesis. The microarray analysis revealed that the differences in morphological and physiological traits between tubers of the two clones are genetically determined since T0 and that is relatively low the number of differentially expressed ESTs across the stages shared between the clones (93). The expression of ESTs for sucrose:sucrose 1-fructosyltransferase (1-SST) and fructan:fructan 1-fructosyltransferase (1-FFT), the two critical genes for fructans polymerization, resulted to be temporarily synchronized and mirror the progress of inulin accumulation and stretching. The expression of ESTs for starch biosynthesis was insignificant throughout the developmental stages of the clones in line with the negligible level of starch into their mature tubers, where inulin was the dominant polysaccharide. Overall, our study disclosed candidate genes underpinning the development and storage of carbohydrates in the tubers of two H. tuberosus clones. A model according to which the steady-state levels of 1-SST and 1-FFT transcripts are developmentally controlled and might represent a limiting factor for inulin accumulation has been provided. Our finding may have significant repercussions for breeding clones with improved levels of inulin for food and chemical industry.

Barley Root Proteome and Metabolome in Response to Cytokinin and Abiotic Stimuli

Cytokinin is a phytohormone involved in the regulation of diverse developmental and physiological processes in plants. Its potential in biotechnology and for development of higher-yield and more resilient plants has been recognized, yet the molecular mechanisms behind its action are far from understood. In this report, the roots of barley seedlings were explored as a new source to reveal as yet unknown cytokinin-responsive proteins for crop improvement. Here we found significant differences reproducibly observed for 178 proteins, for which some of the revealed cytokinin-responsive pathways were confirmed in metabolome analysis, including alterations phenylpropanoid pathway, amino acid biosynthesis and ROS metabolism. Bioinformatics analysis indicated a significant overlap between cytokinin response and response to abiotic stress. This was confirmed by comparing proteome and metabolome profiles in response to drought, salinity or a period of temperature stress. The results illustrate complex abiotic stress response in the early development of model crop plant and confirm an extensive crosstalk between plant hormone cytokinin and response to temperature stimuli, water availability or salinity stress.

Arabidopsis GAAPs interacting with MAPR3 modulate the IRE1-dependent pathway upon endoplasmic reticulum stress

Cell viability requires the maintenance of intracellular homeostasis through the unfolded protein response mediated by receptors localized on the endoplasmic reticulum (ER) membrane. The receptor IRE1 mediates not only various adaptive outputs but also programmed cell death (PCD) under varying stress levels. However, little is known about the mechanism by which the same receptors trigger different responses in plants. Arabidopsis Golgi anti-apoptotic protein 1 (GAAP1) and GAAP3 resist PCD upon ER stress and negatively modulate the adaptive response of the IRE1-bZIP60 pathway through IRE1 association. To elucidate the mechanism underlying the anti-PCD activity of GAAPs, we attempted to isolate interactors of GAAPs by yeast two-hybrid screening. Membrane-associated progesterone receptor 3 (MAPR3) was isolated as one of the factors interacting with GAAP. Mutations in GAAP1/GAAP3 and/or MAPR3 enhanced the sensitivity of seedlings to ER stress. Whole-transcriptome analysis combined with quantitative reverse transcription-PCR and cellular analysis showed that regulated IRE1-dependent decay (RIDD) and autophagy were impaired in mutants mapr3, gaap1mapr3, and gaap3mapr3. MAPR3, GAAP1, and GAAP3 interacted with IRE1B as determined by protein interaction assays. These data suggest that the interaction of GAAP1/GAAP3 with MAPR3 mitigates ER stress to some extent through regulating IRE10-mediated RIDD and autophagy.

BES1-regulated BEE1 controls photoperiodic flowering downstream of blue light signaling pathway in Arabidopsis

BRI1-EMS-SUPPRESSOR 1 (BES1) functions as a key regulator in the brassinosteroid (BR) pathway that promotes plant growth. However, whether BES1 is involved in photoperiodic flowering is unknown. Here we report that BES1 acts as a positive regulator of photoperiodic flowering, but it cannot directly bind FLOWERING LOCUS T (FT) promoter. BR ENHANCED EXPRESSION 1 (BEE1) is the direct target of BES1 and acts downstream of BES1. BEE1 is also a positive regulator of photoperiodic flowering. BEE1 binds directly to the FT chromatin to activate the transcription of FT and promote flowering initiation. More importantly, BEE1 promotes flowering in a blue light photoreceptor CRYPTOCHROME 2 (CRY2)  partially dependent manner, as it physically interacts with CRY2 under the blue light. Furthermore, BEE1 is regulated by both BRs and blue light. The transcription of BEE1 is induced by BRs, and the BEE1 protein is stabilized under the blue light. Our findings indicate that BEE1 is the integrator of BES1 and CRY2 mediating flowering, and BES1-BEE1-FT is a new signaling pathway in regulating photoperiodic flowering.

Plants are Capable of Synthesizing Animal Steroid Hormones

As a result of the findings of scientists working on the biosynthesis and metabolism of steroids in the plant and animal kingdoms over the past five decades, it has become apparent that those compounds that naturally occur in animals can also be found as natural constituents of plants and vice versa, i.e., they have essentially the same fate in the majority of living organisms. This review summarizes the current state of knowledge on the occurrence of animal steroid hormones in the plant kingdom, particularly focusing on progesterone, testosterone, androstadienedione (boldione), androstenedione, and estrogens.

Changes in content of steroid regulators during cold hardening of winter wheat - Steroid physiological/biochemical activity and impact on frost tolerance

The purpose of experiments was to describe the alterations of content of steroid regulators (brassinosteroids, progesterone) during cold hardening of winter wheat. Further we studied physiological and biochemical changes induced by these steroids in cold hardened winter wheat together with estimation of plant frost tolerance. The endogenous brassinosteroid content was elevated in winter wheat during cold hardening while level of progesterone was lowered. A higher content of brassinosteroids (but not progesterone) was connected to better frost tolerance of winter wheat cultivars. Plant supplementation with brassinosteroid (24-epibrassinolide) and progesterone before cold hardening reduced frost damage. Tests with the inhibitors of the biosynthesis of brassinosteroids and progesterone suggested that these steroids are one of players in regulating the antioxidant system in winter wheat during cold hardening. Their role in regulating the expression of Rubisco or the Rubisco activase gene was less clear. Steroid regulators did not affect the content of the stress hormone ABA. Model studies of the membranes, made on a Langmuir bath, showed an increase in the value of the parameter describing differences in membrane compressibility (resulting from stronger interactions among the molecules in the monolayers). This suggests that 24-epibrassinolide and progesterone enter into the lipid layer and - in a similar way to sterols - stabilise the interaction among lipids. It may be significant step for better frost tolerance. The use of steroid regulators (especially brassinosteroids) as agrochemicals improving frost tolerance of winter cereals will be discussed.

Beyond Light: Insights Into the Role of Constitutively Photomorphogenic1 in Plant Hormonal Signaling

Light is an important environmental factor with profound effects in plant growth and development. Constitutively photomorphogenic1 (COP1) is a vital component of the light signaling pathway as a negative regulator of photomorphogenesis. Although the role of COP1 in light signaling has been firmly established for some time, recent studies have proven that COP1 is also a crucial part of multiple plant hormonal regulatory pathways. In this article, we review the available evidence involving COP1 in hormone signaling, its molecular mechanisms, and its contribution to the complicated regulatory network linking light and plant hormone signaling.

Brassinosteroids Affect the Symbiosis Between the AM Fungus Rhizoglomus irregularis and Solanaceous Host Plants

Together with several proteins involved in brassinosteroid (BR) signaling and synthesis, the membrane steroid binding protein 1 (MSBP1) was identified within the interactome of the sucrose transporter of tomato (SlSUT2). We asked whether MSBP1 is also involved in BR signaling as assumed for the AtMSBP1 protein from Arabidopsis and whether it impacts root colonization with arbuscular mycorrhizal (AM) fungi in a similar way as shown previously for SlSUT2. In addition, we asked whether brassinosteroids per se affect efficiency of root colonization by AM fungi. We carried out a set of experiments with transgenic tobacco plants with increased and decreased MSBP1 expression levels. We investigated the plant and the mycorrhizal phenotype of these transgenic plants and tested the involvement of MSBP1 in BR metabolism by application of epi-brassinolide and brassinazole, an inhibitor of BR biosynthesis. We show that the phenotype of the transgenic tobacco plants with increased or reduced MSBP1 expression is consistent with an inhibitory role of MSBP1 in BR signaling. MSBP1 overexpression could be mimicked by brassinazole treatment. Interestingly, manipulation of MSBP1 expression in transgenic tobacco plants not only affected plant growth and development, but also the host plant responses toward colonization with AM fungi, as well as arbuscular architecture. Moreover, we observed that brassinosteroids indeed have a direct impact on the nutrient exchange in AM symbiosis and on the biomass production of colonized host plants. Furthermore, arbuscular morphology is affected by changes in MSBP1 expression and brassinolide or brassinazole treatments. We conclude that host plant growth responses and nutrient exchange within the symbiosis with AM fungi is controlled by brassinosteroids and might be impeded by the MSBP1 protein.

Comparative Proteomic and Physiological Analyses of Two Divergent Maize Inbred Lines Provide More Insights into Drought-Stress Tolerance Mechanisms

Drought stress is the major abiotic factor threatening maize (Zea mays L.) yield globally. Therefore, revealing the molecular mechanisms fundamental to drought tolerance in maize becomes imperative. Herein, we conducted a comprehensive comparative analysis of two maize inbred lines contrasting in drought stress tolerance based on their physiological and proteomic responses at the seedling stage. Our observations showed that divergent stress tolerance mechanisms exist between the two inbred-lines at physiological and proteomic levels, with YE8112 being comparatively more tolerant than MO17 owing to its maintenance of higher relative leaf water and proline contents, greater increase in peroxidase (POD) activity, along with decreased level of lipid peroxidation under stressed conditions. Using an iTRAQ (isobaric tags for relative and absolute quantification)-based method, we identified a total of 721 differentially abundant proteins (DAPs). Amongst these, we fished out five essential sets of drought responsive DAPs, including 13 DAPs specific to YE8112, 107 specific DAPs shared between drought-sensitive and drought-tolerant lines after drought treatment (SD_TD), three DAPs of YE8112 also regulated in SD_TD, 84 DAPs unique to MO17, and five overlapping DAPs between the two inbred lines. The most significantly enriched DAPs in YE8112 were associated with the photosynthesis antenna proteins pathway, whilst those in MO17 were related to C5-branched dibasic acid metabolism and RNA transport pathways. The changes in protein abundance were consistent with the observed physiological characterizations of the two inbred lines. Further, quantitative real-time polymerase chain reaction (qRT-PCR) analysis results confirmed the iTRAQ sequencing data. The higher drought tolerance of YE8112 was attributed to: activation of photosynthesis proteins involved in balancing light capture and utilization; enhanced lipid-metabolism; development of abiotic and biotic cross-tolerance mechanisms; increased cellular detoxification capacity; activation of chaperones that stabilize other proteins against drought-induced denaturation; and reduced synthesis of redundant proteins to help save energy to battle drought stress. These findings provide further insights into the molecular signatures underpinning maize drought stress tolerance.

Ecological genomics of variation in bud-break phenology and mechanisms of response to climate warming in Populus trichocarpa

Spring bud-break phenology is a critical adaptive feature common to temperate perennial woody plants. Understanding the molecular underpinnings of variation in bud-break is important for elucidating adaptive evolution and predicting outcomes relating to climate change. Field and controlled growth chamber tests were used to assess population-wide patterns in bud-break from wild-sourced black cottonwood (Populus trichocarpa) genotypes. We conducted a genome-wide association study (GWAS) with single nucleotide polymorphisms (SNPs) derived from whole genome sequencing to test for loci underlying variation in bud-break. Bud-break had a quadratic relationship with latitude, where southern- and northern-most provenances generally broke bud earlier than those from central parts of the species' range. Reduced winter chilling increased population-wide variation in bud-break, whereas greater chilling decreased variation. GWAS uncovered 16 loci associated with bud-break. Phenotypic changes connected with allelic variation were replicated in an independent set of P. trichocarpa trees. Despite phenotypic similarities, genetic profiles between southern- and northern-most genotypes were dissimilar based on our GWAS-identified SNPs. We propose that the GWAS-identified loci underpin the geographical pattern in P. trichocarpa and that variation in bud-break reflects different selection for winter chilling and heat sum accumulation, both of which can be affected by climate warming.

Plasma membrane proteome analysis identifies a role of barley membrane steroid binding protein in root architecture response to salinity

Although the physiological consequences of plant growth under saline conditions have been well described, understanding the core mechanisms conferring plant salt adaptation has only started. We target the root plasma membrane proteomes of two barley varieties, cvs. Steptoe and Morex, with contrasting salinity tolerance. In total, 588 plasma membrane proteins were identified by mass spectrometry, of which 182 were either cultivar or salinity stress responsive. Three candidate proteins with increased abundance in the tolerant cv. Morex were involved either in sterol binding (a GTPase-activating protein for the adenosine diphosphate ribosylation factor [ZIGA2], and a membrane steroid binding protein [MSBP]) or in phospholipid synthesis (phosphoethanolamine methyltransferase [PEAMT]). Overexpression of barley MSBP conferred salinity tolerance to yeast cells, whereas the knock-out of the heterologous AtMSBP1 increased salt sensitivity in Arabidopsis. Atmsbp1 plants showed a reduced number of lateral roots under salinity, and root-tip-specific expression of barley MSBP in Atmsbp1 complemented this phenotype. In barley, an increased abundance of MSBP correlates with reduced root length and lateral root formation as well as increased levels of auxin under salinity being stronger in the tolerant cv. Morex. Hence, we concluded the involvement of MSBP in phytohormone-directed adaptation of root architecture in response to salinity.

Indole-3-carbinol: a plant hormone combatting cancer

A diet rich in cruciferous vegetables such as cauliflower, broccoli, and cabbage has long been considered healthy, and various epidemiological studies suggest that the consumption of cruciferous vegetables contributes to a cancer-protecting diet. While these vegetables contain a vast array of phytochemicals, the mechanism by which these vegetables counteract cancer is still largely unresolved. Numerous in situ studies have implicated indole-3-carbinol, a breakdown product of the glucosinolate indole-3-ylmethylglucosinolate, as one of the phytochemicals with anti-cancer properties. Indole-3-carbinol influences a range of cellular processes, but the mechanisms by which it acts on cancer cells are slowly being revealed. Recent studies on the role of indole-3-carbinol in Arabidopsis opens the door for cross-kingdom comparisons that can help in understanding the roles of this important phytohormone in both plant biology and combatting cancer.

Multi-Locus Genome-Wide Association Study Reveals the Genetic Architecture of Stalk Lodging Resistance-Related Traits in Maize

Stalk lodging resistance, which is mainly measured by stem diameter (SD), stalk bending strength (SBS), and rind penetrometer resistance (RPR) in maize, seriously affects the yield and quality of maize (Zea mays L.). To dissect its genetic architecture, in this study multi-locus genome-wide association studies for stalk lodging resistance-related traits were conducted in a population of 257 inbred lines, with tropical, subtropical, and temperate backgrounds, genotyped with 48,193 high-quality single nucleotide polymorphisms. The analyses of phenotypic variations for the above traits in three environments showed high broad-sense heritability (0.679, 0.720, and 0.854, respectively). In total, 423 significant Quantitative Trait Nucleotides (QTNs) were identified by mrMLM, FASTmrEMMA, ISIS EM-BLASSO, and pLARmEB methods to be associated with the above traits. Among these QTNs, 29, 34, and 48 were commonly detected by multiple methods or across multiple environments to be related to SD, SBS, and RPR, respectively. The superior allele analyses in 30 elite lines showed that only eight lines contained more than 50% of the superior alleles, indicating that stalk lodging resistance can be improved by the integration of more superior alleles. Among sixty-three candidate genes of the consistently expressed QTNs, GRMZM5G856734 and GRMZM2G116885, encoding membrane steroid-binding protein 1 and cyclin-dependent kinase inhibitor 1, respectively, possibly inhibit cell elongation and division, which regulates lodging resistance. Our results provide the further understanding of the genetic foundation of maize lodging resistance.

The scaffold proteins of lignin biosynthetic cytochrome P450 enzymes

Lignin is a complex and irregular biopolymer of crosslinked phenylpropanoid units in plant secondary cell walls. Its biosynthesis requires three endoplasmic reticulum (ER)-resident cytochrome P450 monooxygenases, C4H, C3'H and F5H, to establish the structural characteristics of its monomeric precursors. These P450 enzymes were reported to associate with each other or potentially with other soluble monolignol biosynthetic enzymes to form an enzyme complex or a metabolon. However, the molecular basis governing such enzyme or pathway organization remains elusive. Here, we show that Arabidopsis membrane steroid-binding proteins (MSBPs) serve as a scaffold to physically organize monolignol P450 monooxygenases, thereby regulating the lignin biosynthetic process. We find that although C4H, C3'H and F5H are in spatial proximity to each other on the ER membrane in vivo, they do not appear to directly interact with each other. Instead, two MSBP proteins physically interact with all three P450 enzymes and, moreover, MSBPs themselves associate as homomers and heteromers on the ER membrane, thereby organizing P450 clusters. Downregulation of MSBP genes does not affect the transcription levels of monolignol biosynthetic P450 genes but substantially impairs the stability and activity of the MSBP-interacting P450 enzymes and, consequently, lignin deposition, and the accumulation of soluble phenolics in the monolignol branch but not in the flavonoid pathway. Our study suggests that MSBP proteins are essential structural components in the ER membrane that physically organize and stabilize the monolignol biosynthetic P450 enzyme complex, thereby specifically controlling phenylpropanoid-monolignol branch biosynthesis.

UVR8 Interacts with BES1 and BIM1 to Regulate Transcription and Photomorphogenesis in Arabidopsis

UV-B light (UV-B radiation) is known to inhibit plant growth, but the mechanism is not well understood. UVR8 (UV RESISTANCE LOCUS 8) is a UV-B light photoreceptor that mediates UV-B light responses in plants. We report here that UV-B inhibits plant growth by repressing plant steroid hormone brassinosteroid (BR)-promoted plant growth. UVR8 physically interacts with the functional dephosphorylated BES1 (BRI1-EMS-SUPPRESSOR1) and BIM1 (BES1-INTERACTING MYC-LIKE 1) transcription factors that mediate BR-regulated gene expression and plant growth to inhibit their activities. Genome-wide gene expression analysis defined a BES1-dependent UV-B-regulated transcriptome, which is enriched with genes involved in cell elongation and plant growth. We further showed that UV-B-activated and nucleus-localized UVR8 inhibited the DNA-binding activities of BES1/BIM1 to directly regulate transcription of growth-related genes. Our results therefore establish that UVR8-BES1/BIM1 interaction represents an early photoreceptor signaling mechanism in plants and serves as an important module integrating light and BR signaling.

Regulation of the membrane structure by brassinosteroids and progesterone in winter wheat seedlings exposed to low temperature

Steroids constitute one of the most important groups of compounds of regulatory properties both in the animal and plant kingdom. In plants, steroids such as brassinosteroids or progesterone, by binding to protein receptors in cell membranes, regulate growth and initiate processes leading to increased tolerance to stress conditions. Due to their structural similarities to sterols, these steroids may also directly interact with cellular membranes. Our aim was to determine the changes of the structural parameters of lipid membranes under the influence of hydrophobic steroid compounds, i.e., 24-epibrassinolide (EBR) and its precursor-24-epicastasterone (ECS) and progesterone (PRO). Lipids were isolated from wheat seedlings with different tolerances to frost, grown at low temperatures (5 °C) for 1.5 and 3 weeks (acclimation process). Control plants were cultured continuously at 20 °C. From galactolipids and phospholipids, the main polar lipid fractions, the monolayers were formed, using a technique of Langmuir trough. EBR and ECS were introduced into monolayers, together with lipids, whereas the PRO was dissolved in the aqueous sub-phase upon which the monolayers were spread. Measurements performed at 25 °C and 10 °C showed a significant action of the tested compounds on the physicochemical properties of the monolayers. EBR and PRO increased the area per lipid molecule in monolayers, resulting in formation of more flexible surface structures while the presence of the ECS induced the opposite effect. The influence of the polarity of lipids and steroids on the interactions in the monolayer was discussed. Lipids extracted from the membranes of wheat with the most tolerance to frost were characterized by the highest fatty acid unsaturation and steroids had a relatively weak effect on the parameters of the structure of their monolayers.

A key enzyme of animal steroidogenesis can function in plants enhancing their immunity and accelerating the processes of growth and development

BACKGROUND

The initial stage of the biosynthesis of steroid hormones in animals occurs in the mitochondria of steroidogenic tissues, where cytochrome P450SCC (CYP11A1) encoded by the CYP11A1 gene catalyzes the conversion of cholesterol into pregnenolone - the general precursor of all the steroid hormones, starting with progesterone. This stage is missing in plants where mitochondrial cytochromes P450 (the mito CYP clan) have not been found. Generating transgenic plants with a mitochondrial type P450 from animals would offer an interesting option to verify whether plant mitochondria could serve as another site of P450 monooxygenase reaction for the steroid hormones biosynthesis.

RESULTS

For a more detailed comparison of steroidogenic systems of Plantae and Animalia, we have created and studied transgenic tobacco and tomato plants efficiently expressing mammalian CYP11A1 cDNA. The detailed phenotypic characterization of plants obtained has shown that through four generations studied, the transgenic tobacco plants have reduced a period of vegetative development (early flowering and maturation of bolls), enlarged biomass and increased productivity (quantity and quality of seeds) as compared to the only empty-vector containing or wild type plants. Moreover, the CYP11A1 transgenic plants show resistance to such fungal pathogen as Botrytis cinerea. Similar valuable phenotypes (the accelerated course of ontogenesis and/or stress resistance) are also visible in two clearly distinct transgenic tomato lines expressing CYP11A1 cDNA: one line (No. 4) has an accelerated rate of vegetative development, while the other (No. 7) has enhanced immunity to abiotic and biotic stresses. The progesterone level in transgenic tobacco and tomato leaves is 3-5 times higher than in the control plants of the wild type.

CONCLUSIONS

For the first time, we could show the compatibility in vivo of even the most specific components of the systems of biosynthesis of steroid hormones in Plantae and Animalia. The hypothesis is proposed and substantiated that the formation of the above-noted special phenotypes of transgenic plants expressing mammalian CYP11A1 cDNA is due to the increased biosynthesis of progesterone that can be considered as a very ancient bioregulator of plant cells and the first real hormone common to plants and animals.

Long photoperiod affects the maize transition from vegetative to reproductive stages: a proteomic comparison between photoperiod-sensitive inbred line and its recurrent parent

Maize (Zea mays L.) is a typical short-day plant that is produced as an important food product and industrial material. The photoperiod is one of the most important evolutionary mechanisms enabling the adaptation of plant developmental phases to changes in climate conditions. There are differences in the photoperiod sensitivity of maize inbred lines from tropical to temperate regions. In this study, to identify the maize proteins responsive to a long photoperiod (LP), the photoperiod-insensitive inbred line HZ4 and its near-isogenic line H496, which is sensitive to LP conditions, were analyzed under long-day conditions using isobaric tags for relative and absolute quantitation. We identified 5259 proteins in maize leaves exposed to the LP condition between the vegetative and reproductive stages. These proteins included 579 and 576 differentially accumulated proteins in H496 and HZ4 leaves, respectively. The differentially accumulated proteins (e.g., membrane, defense, and energy- and ribosome-related proteins) exhibited the opposite trends in HZ4 and H496 plants during the transition from the vegetative stage to the reproductive stage. These results suggest that the photoperiod-associated fragment in H496 plants considerably influences various proteins to respond to the photoperiod sensitivity. Overall, our data provide new insights into the effects of long-day treatments on the maize proteome, and may be useful for the development of new germplasm.

Proteome Profiling of Paulownia Seedlings Infected with Phytoplasma

Phytoplasma is an insect-transmitted pathogen that causes witches' broom disease in many plants. Paulownia witches' broom is one of the most destructive diseases threatening Paulownia production. The molecular mechanisms associated with this disease have been investigated by transcriptome sequencing, but changes in protein abundance have not been investigated with isobaric tags for relative and absolute quantitation. Previous results have shown that methyl methane sulfonate (MMS) can help Paulownia seedlings recover from the symptoms of witches' broom and reinstate a healthy morphology. In this study, a transcriptomic-assisted proteomic technique was used to analyze the protein changes in phytoplasma-infected Paulownia tomentosa seedlings, phytoplasma-infected seedlings treated with 20 and 60 mg·L^-1 MMS, and healthy seedlings. A total of 2,051 proteins were obtained, 879 of which were found to be differentially abundant in pairwise comparisons between the sample groups. Among the differentially abundant proteins, 43 were related to Paulownia witches' broom disease and many of them were annotated to be involved in photosynthesis, expression of dwarf symptom, energy production, and cell signal pathways.

Membrane Proteomics of Arabidopsis Glucosinolate Mutants cyp79B2/B3 and myb28/29

Glucosinolates (Gls) constitute a major group of natural metabolites represented by three major classes (aliphatic, indolic and aromatic) of more than 120 chemical structures. In our previous work, soluble proteins and metabolites in Arabidopsis mutants deficient of aliphatic (myb28/29) and indolic Gls (cyp79B2B3) were analyzed. Here we focus on investigating the changes at the level of membrane proteins in these mutants. Our LC/MS-MS analyses of tandem mass tag (TMT) labeled peptides derived from the cyp79B2/B3 and myb28/29 relative to wild type resulted in the identification of 4,673 proteins, from which 2,171 are membrane proteins. Fold changes and statistical analysis showed 64 increased and 74 decreased in cyp79B2/B3, while 28 increased and 17 decreased in myb28/29. As to the shared protein changes between the mutants, one protein was increased and eight were decreased. Bioinformatics analysis of the changed proteins led to the discovery of three cytochromes in glucosinolate molecular network (GMN): cytochrome P450 86A7 (At1g63710), cytochrome P450 71B26 (At3g26290), and probable cytochrome c (At1g22840). CYP86A7 and CYP71B26 may play a role in hydroxyl-indolic Gls production. In addition, flavone 3'-O-methyltransferase 1 represents an interesting finding as it is likely to participate in the methylation process of the hydroxyl-indolic Gls to form methoxy-indolic Gls. The analysis also revealed additional new nodes in the GMN related to stress and defense activity, transport, photosynthesis, and translation processes. Gene expression and protein levels were found to be correlated in the cyp79B2/B3, but not in the myb28/29.

Transcriptional identification and characterization of differentially expressed genes associated with embryogenesis in radish (Raphanus sativus L.)

Embryogenesis is an important component in the life cycle of most plant species. Due to the difficulty in embryo isolation, the global gene expression involved in plant embryogenesis, especially the early events following fertilization are largely unknown in radish. In this study, three cDNA libraries from ovules of radish before and after fertilization were sequenced using the Digital Gene Expression (DGE) tag profiling strategy. A total of 5,777 differentially expressed transcripts were detected based on pairwise comparison in the three libraries (0_DAP, 7_DAP and 15_DAP). Results from Gene Ontology (GO) and pathway enrichment analysis revealed that these differentially expressed genes (DEGs) were implicated in numerous life processes including embryo development and phytohormones biosynthesis. Notably, some genes encoding auxin response factor (ARF ), Leafy cotyledon1 (LEC1) and somatic embryogenesis receptor-like kinase (SERK ) known to be involved in radish embryogenesis were differentially expressed. The expression patterns of 30 genes including LEC1-2, AGL9, LRR, PKL and ARF8-1 were validated by qRT-PCR. Furthermore, the cooperation between miRNA and mRNA may play a pivotal role in the radish embryogenesis process. This is the first report on identification of DEGs profiles related to radish embryogenesis and seed development. These results could facilitate further dissection of the molecular mechanisms underlying embryogenesis and seed development in radish.

Steroidogenesis in plants--Biosynthesis and conversions of progesterone and other pregnane derivatives

In plants androstanes, estranes, pregnanes and corticoids have been described. Sometimes 17β-estradiol, androsterone, testosterone or progesterone were summarized as sex hormones. These steroids influence plant development: cell divisions, root and shoot growth, embryo growth, flowering, pollen tube growth and callus proliferation. First reports on the effect of applicated substances and of their endogenous occurrence date from the early twenties of the last century. This caused later on doubts on the identity of the compounds. Best investigated is the effect of progesterone. Main steps of the progesterone biosynthetic pathway have been analyzed in Digitalis. Cholesterol-side-chain-cleavage, pregnenolone and progesterone formation as well as the stereospecific reduction of progesterone are described and the corresponding enzymes are presented. Biosynthesis of androstanes, estranes and corticoids is discussed. Possible progesterone receptors and physiological reactions on progesterone application are reviewed.

Eucalyptus urograndis stem proteome is responsive to short-term cold stress

Eucalyptus urograndis is a hybrid eucalyptus of major economic importance to the Brazilian pulp and paper industry. Although widely used in forest nurseries around the country, little is known about the biochemical changes imposed by environmental stress in this species. In this study, we evaluated the changes in the stem proteome after short-term stimulation by exposure to low temperature. Using two-dimensional gel electrophoresis coupled to high-resolution mass spectrometry-based protein identification, 12 proteins were found to be differentially regulated and successfully identified after stringent database searches against a protein database from a closely related species (Eucalyptus grandis). The identification of these proteins indicated that the E. urograndis stem proteome responded quickly to low temperature, mostly by down-regulating specific proteins involved in energy metabolism, protein synthesis and signaling. The results of this study represent the first step in understanding the molecular and biochemical responses of E. urograndis to thermal stress.

Disturbances in production of progesterone and their implications in plant studies

Progesterone is a mammalian hormone that has also been discovered in plants but its physiological function in plants is not explained. Experiments using inhibitors of progesterone synthesis and binding would be useful in studies on the significance of this compound in plants. Until now, trilostane and mifepristone have been used in medical sciences as progesterone biosynthesis and binding inhibitors, respectively. We tested these synthetic steroids for the first time in plants and found that they reduced the content of progesterone in wheat. The aim of further experiments was to answer whether the potential disturbances in the production/binding of progesterone, influence resistance to environmental stress (drought) and the development of wheat. Inhibitors and progesterone were applied to plants via roots in a concentration of 0.25-0.5mg/l water. Both inhibitors lowered the activity of CO2 binding enzyme (Rubisco) in wheat exposed to drought stress and trilostane additionally lowered the chlorophyll content. However, trilostane-treated plants were rescued by treatment with exogenous progesterone. The inhibitors also modulated the development of winter wheat, which indicated the significance of steroid regulators and their receptors in this process. In this study, in addition to progesterone and its inhibitors, brassinosteroid (24-epibrassinolide) and an inhibitor of biosynthesis of brassinosteroids were also applied. Mifepristone inhibited the generative development of wheat (like 24-epibrassinolide), while trilostane (like progesterone and an inhibitor of biosynthesis of brassinosteroids) stimulated the development. We propose a model of steroid-induced regulation of the development of winter wheat, where brassinosteroids act as inhibitors of generative development, while progesterone or other pregnane derivatives act as stimulators.

Brassinosteroids promote Arabidopsis pollen germination and growth

Pollen tubes are among the fastest tip-growing plant cells and represent an excellent experimental system for studying the dynamics and spatiotemporal control of polarized cell growth. However, investigating pollen tube tip growth in the model plant Arabidopsis remains difficult because in vitro pollen germination and pollen tube growth rates are highly variable and largely different from those observed in pistils, most likely due to growth-promoting properties of the female reproductive tract. We found that in vitro grown Arabidopsis pollen respond to brassinosteroid (BR) in a dose-dependent manner. Pollen germination and pollen tube growth increased nine- and fivefold, respectively, when media were supplemented with 10 µM epibrassinolide (epiBL), resulting in growth kinetics more similar to growth in vivo. Expression analyses show that the promoter of one of the key enzymes in BR biosynthesis, CYP90A1/CPD, is highly active in the cells of the reproductive tract that form the pathway for pollen tubes from the stigma to the ovules. Pollen tubes grew significantly shorter through the reproductive tract of a cyp90a1 mutant compared to the wild type, or to a BR perception mutant. Our results show that epiBL promotes pollen germination and tube growth in vitro and suggest that the cells of the reproductive tract provide BR compounds to stimulate pollen tube growth.

The sucrose transporter SlSUT2 from tomato interacts with brassinosteroid functioning and affects arbuscular mycorrhiza formation

Mycorrhizal plants benefit from the fungal partners by getting better access to soil nutrients. In exchange, the plant supplies carbohydrates to the fungus. The additional carbohydrate demand in mycorrhizal plants was shown to be balanced partially by higher CO2 assimilation and increased C metabolism in shoots and roots. In order to test the role of sucrose transport for fungal development in arbuscular mycorrhizal (AM) tomato, transgenic plants with down-regulated expression of three sucrose transporter genes were analysed. Plants that carried an antisense construct of SlSUT2 (SlSUT2as) repeatedly exhibited increased mycorrhizal colonization and the positive effect of plants to mycorrhiza was abolished. Grafting experiments between transgenic and wild-type rootstocks and scions indicated that mainly the root-specific function of SlSUT2 has an impact on colonization of tomato roots with the AM fungus. Localization of SISUT2 to the periarbuscular membrane indicates a role in back transport of sucrose from the periarbuscular matrix into the plant cell thereby affecting hyphal development. Screening of an expression library for SlSUT2-interacting proteins revealed interactions with candidates involved in brassinosteroid (BR) signaling or biosynthesis. Interaction of these candidates with SlSUT2 was confirmed by bimolecular fluorescence complementation. Tomato mutants defective in BR biosynthesis were analysed with respect to mycorrhizal symbiosis and showed indeed decreased mycorrhization. This finding suggests that BRs affect mycorrhizal infection and colonization. If the inhibitory effect of SlSUT2 on mycorrhizal growth involves components of BR synthesis and of the BR signaling pathway is discussed.

Differential expression of the brassinosteroid receptor-encoding BRI1 gene in Arabidopsis

Brassinosteroid (BR)-regulated growth and development in Arabidopsis depends on BRASSINOSTEROID INSENSITIVE 1 (BRI1), the BR receptor that is responsible for initiating the events of BR signalling. We analysed the temporal and spatial regulation of BRI1 expression using stable transgenic lines that carried BRI1 promoter:reporter fusions. In both seedlings and mature plants the tissues undergoing elongation or differentiation showed elevated BRI1 gene activity, and it could be demonstrated that in the hypocotyl this was accompanied by accumulation of the BRI1 transcript and its receptor protein product. In seedlings the BRI1 promoter was also found to be under diurnal regulation, determined primarily by light repression and a superimposed circadian control. To determine the functional importance of transcriptional regulation we complemented the severely BR insensitive bri1-101 mutant with a BRI1-luciferase fusion construct that was driven by promoters with contrasting specificities. Whereas the BRI1 promoter-driven transgene fully restored the wild phenotype, expression from the photosynthesis-associated CAB3 and the vasculature-specific SUC2 and ATHB8 promoters resulted in plants with varying morphogenic defects. Our results reveal complex differential regulation of BRI1 expression, and suggest that by influencing the distribution and abundance of the receptor this regulation can enhance or attenuate BR signalling.

Isolation and characterization of the brassinosteroid receptor gene (GmBRI1) from Glycine max

Brassinosteroids (BRs) constitute a group of steroidal phytohormones that contribute to a wide range of plant growth and development functions. The genetic modulation of BR receptor genes, which play major roles in the BR signaling pathway, can create semi-dwarf plants that have great advantages in crop production. In this study, a brassinosteroid insensitive gene homologous with AtBRI1 and other BRIs was isolated from Glycine max and designated as GmBRI1. A bioinformatic analysis revealed that GmBRI1 shares a conserved kinase domain and 25 tandem leucine-rich repeats (LRRs) that are characteristic of a BR receptor for BR reception and reaction and bear a striking similarity in protein tertiary structure to AtBRI1. GmBRI1 transcripts were more abundant in soybean hypocotyls and could be upregulated in response to exogenous BR treatment. The transformation of GmBRI1 into the Arabidopsis dwarf mutant bri1-5 restored the phenotype, especially regarding pod size and plant height. Additionally, this complementation is a consequence of a restored BR signaling pathway demonstrated in the light/dark analysis, root inhibition assay and BR-response gene expression. Therefore, GmBRI1 functions as a BR receptor to alter BR-mediated signaling and is valuable for improving plant architecture and enhancing the yield of soybean.

From squalene to brassinolide: the steroid metabolic and signaling pathways across the plant kingdom

The plant steroid hormones, brassinosteroids (BRs), and their precursors, phytosterols, play major roles in plant growth, development, and stress tolerance. Here, we review the impressive progress made during recent years in elucidating the components of the sterol and BR metabolic and signaling pathways, and in understanding their mechanism of action in both model plants and crops, such as Arabidopsis and rice. We also discuss emerging insights into the regulations of these pathways, their interactions with other hormonal pathways and multiple environmental signals, and the putative nature of sterols as signaling molecules.

Endogenous progesterone and its cellular binding sites in wheat exposed to drought stress

Progesterone is a basic hormone that regulates the metabolism in mammals. The presence of this compound has also been found in certain plants. It is believed that progesterone can regulate growth processes and resistance to stress, however, its precise role in plants remains unknown. The research conducted in this study was aimed at analyzing the content of endogenous progesterone and its cellular binding sites in the leaves of spring wheat exposed to drought. Changes were studied in two cultivars of wheat - a cultivar sensitive to drought (Katoda) and tolerant cultivar (Monsun). Plants had undergone periodic droughts during the seedling stage or in the phase of heading. The occurrence of free progesterone as well as its conjugated forms was observed in wheat studied. The amount of progesterone ranged from 0.2 to 5.8pmolgFW(-1) and was dependent on the cultivar, age of the plants, stage of development and fluctuated as a result of the exposure to drought. Cv. Katoda responded to a water deficit by lowering the amount of progesterone and cv. Monsun by increasing its level. Progesterone in plants grown in limited water conditions occurred primarily in a free form. While in the optimal watering conditions, some of its pool was found in the form of conjugates. In the spring wheat the occurrence of binding sites for progesterone was detected in cell membranes, cytoplasm and nuclei in the range of 10-36fmol/mg of protein. The wheat cultivars tested, Monsun and Katoda, differ in their concentration of cellular binding sites for progesterone. This number varied in the individual fractions during different stages of plant development and due to the effect of drought stress. The number of binding sites for progesterone located in the membrane fraction of seedlings and flag leaves increased significantly under drought in the cv. Katoda (35-46%), but did not change in the cv. Monsun. Whereas the number of cytoplasmic progesterone binding sites increased during the drought in the cv. Monsun (about 50%), they did not change in the cv. Katoda. Changes in the amount of progesterone and its binding sites in the cell under the influence of drought were then different depending on whether the cultivar was tolerant or sensitive to drought. The possibility of utilizing these changes as markers of drought resistance is discussed. The results obtained suggest that progesterone is a part of wheat response to stress factors (drought).

The effects of a stimulating intron on the expression of heterologous genes in Arabidopsis thaliana

Introns are often added to transgenes to increase expression, although the mechanism through which introns stimulate gene expression in plants and other eukaryotes remains mysterious. While introns vary in their effect on expression, it is unknown whether different genes respond similarly to the same stimulatory intron. Furthermore, the degree to which gene regulation is preserved when expression is increased by an intron has not been thoroughly investigated. To test the effects of the same intron on the expression of a range of genes, GUS translational fusions were constructed using the promoters of eight Arabidopsis genes whose expression was reported to be constitutive (GAE1, CNGC2 and ROP10), tissue specific (ADL1A, YAB3 and AtAMT2) or regulated by light (ULI3 and MSBP1). For each gene, a fusion containing the first intron from the UBQ10 gene was compared to fusions containing the gene's endogenous first intron (if the gene has one) or no intron. In every case, the UBQ10 intron increased expression relative to the intronless control, although the magnitude of the change and the level of expression varied. The UBQ10 intron also changed the expression patterns of the CNGC2 and YAB3 fusions to include strong activity in roots, indicating that tissue specificity was disrupted by this intron. In contrast, the regulation of the ULI3 and MSBP1 genes by light was preserved when their expression was stimulated by the intron. These findings have important implications for biotechnology applications in which a high level of transgene expression in only certain tissues is desired.

Response to metal stress of Nicotiana langsdorffii plants wild-type and transgenic for the rat glucocorticoid receptor gene

Recently our findings have shown that the integration of the gene coding for the rat gluco-corticoid receptor (GR receptor) in Nicotiana langsdorffii plants induced morphophysiological effects in transgenic plants through the modification of their hormonal pattern. Phytohormones play a key role in plant responses to many different biotic and abiotic stresses since a modified hormonal profile up-regulates the activation of secondary metabolites involved in the response to stress. In this work transgenic GR plants and isogenic wild type genotypes were exposed to metal stress by treating them with 30ppm cadmium(II) or 50ppm chromium(VI). Hormonal patterns along with changes in key response related metabolites were then monitored and compared. Heavy metal up-take was found to be lower in the GR plants. The transgenic plants exhibited higher values of S-abscisic acid (S-ABA) and 3-indole acetic acid (IAA), salicylic acid and total polyphenols, chlorogenic acid and antiradical activity, compared to the untransformed wild type plants. Both Cd and Cr treatments led to an increase in hormone concentrations and secondary metabolites only in wild type plants. Analysis of the results suggests that the stress responses due to changes in the plant's hormonal system may derive from the interaction between the GR receptor and phytosteroids, which are known to play a key role in plant physiology and development.

Studies on the rice LEAF INCLINATION1 (LC1), an IAA-amido synthetase, reveal the effects of auxin in leaf inclination control

The angle of rice leaf inclination is an important agronomic trait and closely related to the yields and architecture of crops. Although few mutants with altered leaf angles have been reported, the molecular mechanism remains to be elucidated, especially whether hormones are involved in this process. Through genetic screening, a rice gain-of-function mutant leaf inclination1, lc1-D, was identified from the Shanghai T-DNA Insertion Population (SHIP). Phenotypic analysis confirmed the exaggerated leaf angles of lc1-D due to the stimulated cell elongation at the lamina joint. LC1 is transcribed in various tissues and encodes OsGH3-1, an indole-3-acetic acid (IAA) amido synthetase, whose homolog of Arabidopsis functions in maintaining the auxin homeostasis by conjugating excess IAA to various amino acids. Indeed, recombinant LC1 can catalyze the conjugation of IAA to Ala, Asp, and Asn in vitro, which is consistent with the decreased free IAA amount in lc1-D mutant. lc1-D is insensitive to IAA and hypersensitive to exogenous BR, in agreement with the microarray analysis that reveals the altered transcriptions of genes involved in auxin signaling and BR biosynthesis. These results indicate the crucial roles of auxin homeostasis in the leaf inclination control.

Protein-protein and protein-membrane associations in the lignin pathway

Supramolecular organization of enzymes is proposed to orchestrate metabolic complexity and help channel intermediates in different pathways. Phenylpropanoid metabolism has to direct up to 30% of the carbon fixed by plants to the biosynthesis of lignin precursors. Effective coupling of the enzymes in the pathway thus seems to be required. Subcellular localization, mobility, protein-protein, and protein-membrane interactions of four consecutive enzymes around the main branch point leading to lignin precursors was investigated in leaf tissues of Nicotiana benthamiana and cells of Arabidopsis thaliana. CYP73A5 and CYP98A3, the two Arabidopsis cytochrome P450s (P450s) catalyzing para- and meta-hydroxylations of the phenolic ring of monolignols were found to colocalize in the endoplasmic reticulum (ER) and to form homo- and heteromers. They moved along with the fast remodeling plant ER, but their lateral diffusion on the ER surface was restricted, likely due to association with other ER proteins. The connecting soluble enzyme hydroxycinnamoyltransferase (HCT), was found partially associated with the ER. Both HCT and the 4-coumaroyl-CoA ligase relocalized closer to the membrane upon P450 expression. Fluorescence lifetime imaging microscopy supports P450 colocalization and interaction with the soluble proteins, enhanced by the expression of the partner proteins. Protein relocalization was further enhanced in tissues undergoing wound repair. CYP98A3 was the most effective in driving protein association.

The cyclophilin ROC1 links phytochrome and cryptochrome to brassinosteroid sensitivity

Although multiple photoreceptors converge to control common aspects of seedling de-etiolation, we are relatively ignorant of the genes acting at or downstream of their signalling convergence. To address this issue we screened for mutants under a mixture of blue plus far-red light and identified roc1-1D. The roc1-1D mutant, showing elevated expression of the ROTAMASE CYCLOPHILIN 1 (ROC1/AtCYP18-3) gene, and partial loss-of function roc1 alleles, has defects in phytochrome A (phyA)-, cryptochrome 1 (cry1)- and phytochrome B (phyB)-mediated de-etiolation, including long hypocotyls under blue or far-red light. These mutants show elevated sensitivity to brassinosteroids in the light but not in the dark. Mutations at brassinosteroid signalling genes and the application of a brassinosteroid synthesis inhibitor eliminated the roc1 and roc1-D phenotypes. The roc1 and roc1-D mutants show altered patterns of phosphorylation of the transcription factor BES1, a known point of control of sensitivity to brassinosteroids, which correlate with the expression levels of genes directly targeted by BES1. We propose a model where perception of light by phyA, cry1 or phyB activates ROC1 (at least in part by enhancing its expression). This in turn reduces the intensity of brassinosteroid signalling and fine-tunes seedling de-etiolation.

E3-independent ubiquitination of AtMAPR/MSBP1

AtMAPR5/MSBP1 and its homologs can be ubiquitinated in the absence of E3 ligase in in vitro ubiquitination assays. Ubiquitinated AtMAPR3, AtMAPR5/MSBP1, and AtMAPR2 were identified using LC-MS/MS. Analysis of trypsin-released signature peptides showed that this E3-independent ubiquitination of AtMAPR3, AtMAPR5/MSBP1, and AtMAPR2 was dominated by mono-ubiquitination at multiple sites. Unlike AtUBC8-type E2s, AtUBC36 was not able to transfer ubiquitin to AtMAPR2. The truncated mutants AtMAPR2Δ1-10, AtMAPR2Δ1-30, and AtMAPR2_1-73 could also be ubiquitinated. The presence of a ubiquitin-binding domain (UBD) allows proteins to be ubiquitinated independently of E3 ligases. However, AtMAPRs do not contain any known UBD. In vitro ubiquitination of AtMAPR2 observed in this study will be further studied in biochemical and physiological aspects.

Fluorescent castasterone reveals BRI1 signaling from the plasma membrane

Receptor-mediated endocytosis is an integral part of signal transduction as it mediates signal attenuation and provides spatial and temporal dimensions to signaling events. One of the best-studied leucine-rich repeat receptor-like kinases in plants, BRASSINOSTEROID INSENSITIVE 1 (BRI1), perceives its ligand, the brassinosteroid (BR) hormone, at the cell surface and is constitutively endocytosed. However, the importance of endocytosis for BR signaling remains unclear. Here we developed a bioactive, fluorescent BR analog, Alexa Fluor 647-castasterone (AFCS), and visualized the endocytosis of BRI1-AFCS complexes in living Arabidopsis thaliana cells. Impairment of endocytosis dependent on clathrin and the guanine nucleotide exchange factor for ARF GTPases (ARF-GEF) GNOM enhanced BR signaling by retaining active BRI1-ligand complexes at the plasma membrane. Increasing the trans-Golgi network/early endosome pool of BRI1-BR complexes did not affect BR signaling. Our findings provide what is to our knowledge the first visualization of receptor-ligand complexes in plants and reveal clathrin- and ARF-GEF-dependent endocytic regulation of BR signaling from the plasma membrane.

Alleviation of salt stress in wheat seedlings by mammalian sex hormones

BACKGROUND

Salinity is one of the most serious constraints facing agriculture today. Some mechanical, chemical and biological approaches are being pursued to cope with soil salinity. Although exogenously treated mammalian sex hormones (MSHs), progesterone, β-estradiol and androsterone, activate significant effects in various biological aspects in plants growing under normal conditions, there is no report investigating their effects on plants growing under salt stress. The present study aimed to investigate whether MSHs could alleviate the destructive effect of salt stress on wheat seedlings and thereby increase their salt tolerance. Wheat leaves were sprayed with 10(-6), 10(-8) and 10(-10) mol L(-1) concentrations of MSH on the ninth day after sowing. MSH-treated seedlings (10-day-old seedlings) were subjected to salt stress for 5 days (between days 10 and 15).

RESULTS

At all the concentrations tested, MSH treatment provided a significant protection against to detrimental effects of salt stress in wheat seedlings. It improved dry weight, sugar, proline, protein, chlorophyll and glutathione contents in comparison to salinity alone. Similarly, superoxide dismutase, peroxidase, catalase, ascorbate peroxidase and nitrate reductase activities also were augmented by MSH treatment. On the other hand, increases in lipid peroxidation level, superoxide production and hydrogen peroxide content arising from salt treatment were reduced by MSH treatment. The highest salt tolerance was obtained at the concentrations of 10(-6) mol L(-1) for progesterone and 10(-8) mol L(-1) for β-estradiol and for androsterone.

CONCLUSION

MSHs could be used effectively to protect wheat seedlings from the destructive effects of salt stress by stimulating both enzymatic and non-enzymatic antioxidant mechanism and by promoting levels of osmotic protectants such as proline and sugars resulting in osmotic adjustment, carbon storage and radical scavenging in plants.