Brassinosteroid Levels Research Articles

The dehiscence process in Panax ginseng seeds and the stigmasterol biosynthesis pathway in terms of metabolomics

BackgroundGinseng, officially known as Panax ginseng Meyer, has been traditionally used as a medicinal herb, particularly in Asia. Ginseng is propagated from seeds; however, seed germination is challenging, especially in its natural environment on farms. The seeds typically exhibit morphophysiological dormancy and require release from both morphological and physiological dormancy before germination. Although some studies have proposed methods for increasing seed germination rates, the underlying mechanisms of its dormancy release process remain unclear. Here, we investigated metabolic alterations during dehiscence in P. ginseng to determine their potential roles in dormancy release. MethodsWe compared the ginseng seed metabolome before and after dehiscence and the ginsenoside and phytosterol compositions of the seeds in both periods in the presence of related enzymes. ResultsAfter seed dehiscence, the sugar, amino acid, and squalene concentrations were significantly altered, phytosterols associated with the stigmasterol biosynthesis pathway were increased, while ginsenoside and brassinosteroid levels were not significantly altered. In addition, squalene epoxidase, cycloartenol synthase, 24-methylenesterol C-methyltransferase, and the stigmasterol biosynthesis pathway were activated. ConclusionOverall, our findings suggest that morphological activities that facilitate ginseng seed growth are the primary phenomena occurring during the dehiscence process. This study improves the understanding of P. ginseng germination processes and promotes further research of its germination and cultivation.

The brassinosteroid biosynthesis enzyme gene PeCPD improves plant growth and salt tolerance in Populus tomentosa

A major challenge in the development of novel industrial woody crops lies in the trade-offs underlying plant growth, wood quality and abiotic stress tolerance. Single gene modifications in perennial species often lead to improvements in only one of these three processes. However, brassinosteroids (BRs) affect these three aspects, thus a BRs biosynthesis enzyme gene, PeCPD (Populus euphratica Oliv. Constitutive Photomorphogenenic Dwarf), was selected for this goal. PeCPD was mainly expressed in stems and leaves, and showed rapid responses to salt treatment. Plant height and biomass were improved in the PeCPD overexpressed lines, which was accompanied by the promotion of xylem differentiation and the reduction of pith size, consequently improving timber quality, relative to the wild type Populus tomentosa Carr. The transgenic lines also showed higher salt tolerance relative to the wild type, as indicated by less visual injuries and lower reactive oxygen species pressure. This was partly due to increased levels of soluble protein as well as higher superoxide dismutase (SOD) activity and proline level. Our results demonstrated the PeCPD overexpression mediates the trade-off between growth and abiotic stress adaptation in woody plants. The PeCPD overexpression modified the gene expression of BRs biosynthesis and metabolic process, which enhanced BRs response as indicated by improved transcript level of BRs signaling component. Our results showed that modifying PeCPD has a great potential for jointly improving growth, timber quality and abiotic stress tolerance in woody plants.

Overexpression of GmMYB14 improves high-density yield and drought tolerance of soybean through regulating plant architecture mediated by the brassinosteroid pathway.

SummaryMYB transcription factors (TFs) have been reported to regulate the biosynthesis of secondary metabolites, as well as to mediate plant adaption to abiotic stresses, including drought. However, the roles of MYB TFs in regulating plant architecture and yield potential remain poorly understood. Here, we studied the roles of the dehydration‐inducible GmMYB14 gene in regulating plant architecture, high‐density yield and drought tolerance through the brassinosteroid (BR) pathway in soybean. GmMYB14 was shown to localize to nucleus and has a transactivation activity. Stable GmMYB14‐overexpressing (GmMYB14‐OX) transgenic soybean plants displayed a semi‐dwarfism and compact plant architecture associated with decreased cell size, resulting in a decrease in plant height, internode length, leaf area, leaf petiole length and leaf petiole angle, and improved yield in high density under field conditions. Results of the transcriptome sequencing suggested the involvement of BRs in regulating GmMYB14‐OX plant architecture. Indeed, GmMYB14‐OX plants showed reduced endogenous BR contents, while exogenous application of brassinolide could partly rescue the phenotype of GmMYB14‐OX plants. Furthermore, GmMYB14 was shown to directly bind to the promoter of GmBEN1 and up‐regulate its expression, leading to reduced BR content in GmMYB14‐OX plants. GmMYB14‐OX plants also displayed improved drought tolerance under field conditions. GmBEN1 expression was also up‐regulated in the leaves of GmMYB14‐OX plants under polyethylene glycol treatment, indicating that the GmBEN1‐mediated reduction in BR level under stress also contributed to drought/osmotic stress tolerance of the transgenic plants. Our findings provided a strategy for stably increasing high‐density yield and drought tolerance in soybean using a single TF‐encoding gene.

Plant Triterpenoid Crosstalk: The Interaction of Brassinosteroids and Phytoecdysteroids in Lepidium sativum.

Plant steroid alcohols, plant sterols, are essential components of cell membranes that perform many functions. Their most prominent function is maintaining membrane semipermeability and regulating its fluidity through their specific interaction with phospholipids and membrane proteins. This work is focused on the study of the interaction of two groups of plant sterols, brassinosteroids (BRs) and phytoecdysteroids (PE). Steroid substances belonging to both groups are important signaling molecules essential for plant growth and development, but while the first group has all the known attributes of plant hormones, the second lacks hormonal function in plants. The aim of this preliminary study was to determine at what concentration level and to what extent substances of this type are able to interact with each other, and thus influence the early growth and development of a plant. It was found that exogenously applied PE 20-hydroxyecdysone (20E) significantly reduced the level of endogenous BRs in four-day-old garden cress (Lepidium sativum) seedlings. On the other hand, exogenously applied BRs, 24-epibrassinolide (epiBL), caused the opposite effect. Endogenous 20E was further detected at the picogram level in garden cress seedlings. Thus, this is the first report indicating that this plant species is PE-positive. The level of endogenous 20E in garden cress seedlings can be decreased by exogenous epiBL, but only at a relatively high concentration of 1·10−6 M in a culture medium. The image analysis of garden cress seedlings revealed that the length of shoot is affected neither by exogenous BRs nor PE, whereas the root length varies depending on the type and concentration of steroid applied.

Rice stripe virus suppresses jasmonic acid-mediated resistance by hijacking brassinosteroid signaling pathway in rice.

Rice stripe virus (RSV) is one of the most destructive viral diseases affecting rice production. However, so far, only one RSV resistance gene has been cloned, the molecular mechanisms underlying host-RSV interaction are still poorly understood. Here, we show that increasing levels or signaling of brassinosteroids (BR) and jasmonic acid (JA) can significantly enhance the resistance against RSV. On the contrary, plants impaired in BR or JA signaling are more susceptible to RSV. Moreover, the enhancement of RSV resistance conferred by BR is impaired in OsMYC2 (a key positive regulator of JA response) knockout plants, suggesting that BR-mediated RSV resistance requires active JA pathway. In addition, we found that RSV infection suppresses the endogenous BR levels to increase the accumulation of OsGSK2, a key negative regulator of BR signaling. OsGSK2 physically interacts with OsMYC2, resulting in the degradation of OsMYC2 by phosphorylation and reduces JA-mediated defense to facilitate virus infection. These findings not only reveal a novel molecular mechanism mediating the crosstalk between BR and JA in response to virus infection and deepen our understanding about the interaction of virus and plants, but also suggest new effective means of breeding RSV resistant crops using genetic engineering.

Brassinosteroids mediate the effect of high temperature during anthesis on the pistil activity of photo-thermosensitive genetic male-sterile rice lines

Brassinosteroids (BRs) play critical roles in a wide range of plant developmental processes. However, it is unknown whether and how BRs mediate the effect of high temperature (HT) stress during anthesis on the pistil activity of photo-thermosensitive genetic male-sterile (PTSGMS) rice (Oryza sativa L.) lines. This study investigated the question. Three pot-grown PTSGMS rice lines were subjected to HT stress during anthesis. The contents of 24-epibrassinolide (24-EBL) and 28-homobrassinolide (28-HBL), the major forms of BR in rice plants, and levels of reactive oxygen species (ROS) or antioxidants (AOS), hydrogen peroxide (H2O2), 1-aminocylopropane-1-carboxylic acid (ACC), ascorbic acid (AsA), and catalase activity in pistils, were determined. HT stress significantly reduced the contents of both 24-EBL and 28-EBL relative to those under normal temperatures, but the reduction varied by PTSGMS line. A line with higher BR contents under HT stress showed lower contents of ACC and H2O2, higher catalase activity and AsA content in pistils, and higher fertilization rate, seed-setting rate, and seed yield when the line was crossed with a restorer line, indicating that higher levels of BRs increase HT stress resistance. Applying 24-EBL, 28-HBL or an inhibitor of BR biosynthesis confirmed the roles of BRs in response to HT stress. The results suggest that BRs mediate the effect of HT stress on pistil activity during anthesis and alleviate the harm of HT stress by increasing AOS and suppressing ROS generation.

Physiological and transcriptomic analyses of brassinosteroid function in moso bamboo (Phyllostachys edulis) seedlings.

This study demonstrates that brassinosteroid is essential for seedling and shoot growth in moso bamboo. The shoot of moso bamboo is known to grow extremely fast. The roles of phytohormones in such fast growth of bamboo shoot remain unclear. Here we reported that endogenous brassinosteroid (BR) is a major factor promoting bamboo shoot internode elongation. Reducing endogenous brassinosteroid level by its biosynthesis inhibitor propiconazole stunted shoot growth in seedling stage, whereas exogenous BR application promoted scale leaf elongation and the inclination of lamina joint of leaves and scale leaves. Genome-wide transcriptome analysis identified hundreds of genes whose expression levels are altered by BR and propiconazole in shoots and roots of bamboo seedling. The data show that BR regulates cell wall-related genes, hydrogen peroxide catabolic genes, and auxin-related genes. Our study demonstrates an essential role of BR in fast growth bamboo shoots and identifies a large number of BR-responsive genes in bamboo seedlings.

Overexpression of ZmDWF4 improves major agronomic traits and enhances yield in maize

Brassinosteroids (BRs) are a class of plant-specific steroid hormones and play an essential role in plant growth and development. The DWARF4 (DWF4) gene encodes a C-22 hydroxylase, which is a rate-limiting enzyme in BR biosynthesis pathway. Here, the DWF4 (ZmDWF4) in maize (Zea mays L.), the ortholog of Arabidopsis DWF4 (CYP90B1), was transformed into elite inbred Q319 and driven maize ubiquitin promoter. In transgenic lines, the level of the endogenous BR precursor canosterone (CS) was significantly enhanced. ZmDWF4 overexpression greatly improved grain yield per ear from 28.3 to 33.5% in transgenic lines compared with that in non-transgenic Q319 plants. Moreover, ZmDWF4 overexpression significantly enhanced heterosis of combinations by increasing both seed number and seed weight up to 20.4% in transgenic hybrids. Further analysis revealed that ZmDWF4 overexpression significantly improved several agronomic traits and leaf photosynthetic ability in transgenic lines. Finally, RNA-seq analysis suggested that overexpressing ZmDWF4 improved cell growth, cell division, and nutrient assimilation in transgenic kernels. Altogether, our results demonstrate that manipulating BR level by overexpressing ZmDWF4 effectively improves maize agronomic traits, and thus, provides a useful biotechnological strategy for the genetic improvement and further commercially favorable maize breeding.

Effect on morphological characters in Eucalyptus tereticornis Sm. at juvenile stage under the influence of moisture stress and mitigation by Brassionosteroids and sucrose

An experiment was carried out to study the effects of brassinosteroids and sucrose under moisture on the morphological of Eucalyptus tereticornis Sm. at juvenile stage under controlled condition in nursery. The experiment was conducted with the aim of investigating the study the effect of moisture stress levels on growth and physiological characters also to establish the effective combination of BRs and sucrose to combat moisture stress. The study was carried out on the clonal seedlings P-23 of Eucalyptus tereticornis at the Department of Forestry, CCSHAU, Hisar. The clonal seedlings were planted in pots in nursery containing sand and soil in 2:1 proportion. Mineral composition of the pot soil was assessed before planting the Eucalyptus tereticornis plants. All the pots were received normal watering till 90 days of seedling growth. Three months old potted seedlings were subjected to moisture stress (M1 to M3) by withholding water. The different levels of brassinosteroids (0, 5, 10, 15 and 20 ppm) and sucrose (0, 1, 3 and 5% (w/v) were applied to the seedlings. It was observed that increment in shoot length, root length, fresh and dry biomass of fine root, coarse root and total plant biomass significantly declined under moisture stress. But in case of the root length, fresh and dry weight of fine root and coarse root increased and total plant fresh and dry weight decreased with increased the moisture stress levels (M1 to M3).

Genomic analyses of the crosstalk between gibberellins and brassinosteroids metabolisms in tea plant (Camellia sinensis (L.) O. Kuntze)

Endogenous phytohormones gibberellins (GAs) and brassinosteroids (BRs) are associated with the development and growth of higher plants, but the crosstalk between them in leaves of tea plant is unclear. We determined whether or not a crosstalk exists between GAs and BRs at three developmental stages of tea leaves. We performed phytohormone measurement, phenotypic analysis, cytological–anatomical structural analysis, RT-qPCR analysis, and protein–protein interaction (PPI) prediction to obtain physiological, biochemical, and bioinformatic evidences. Leaf area, spongy tissue cell expansion, and GAs- and BRs-related gene expressions were regulated by the crosstalk between GAs and BRs. GAs levels positively correlated with BRs levels at three developmental stages of tea leaves. GAs levels positively correlated with the expression levels of CsCPD (Cytochrome P450 90A1) and CsDWF4 (Dwarf4), which are involved in BRs biosynthesis pathway at three developmental stages of tea leaves. The expression of CsGA20ox1 (Gibberellin 20 oxidase 1), a gene involved in the GAs biosynthesis pathway, positively correlated with GAs and BRs levels at three developmental stages of tea leaves. These results suggested that CsGA20ox1, CsCPD, and CsDWF4 might play regulative roles in the crosstalk between GAs and BRs at the developmental stages of tea leaves. Our findings provided a new and feasible strategy to understand the crosstalk between the GAs and BRs metabolism pathways.

Brassinosteroids in Plant Tolerance to Abiotic Stress

Brassinosteroids (BRs) are a group of plant steroid hormones with multiple roles in plant growth, development, and responses to stresses. In plants, BR deficiencies impair vital physiological processes and cause phenotypic abnormalities. A large number of studies show that BRs can positively influence plant responses to abiotic stresses such as heat, cold, drought, salinity, pesticides, and heavy metals. However, the underlying mechanisms of BR-induced stress tolerance are largely unclear. BR perception takes place in the cell surface by BR receptors, leading to a cascade of phosphorylation events to activate the central transcription factor BRASSINAZOLE-RESISTANT1 (BZR1) that controls the transcription of BR-responsive genes in the nucleus. BRs improve photosynthetic efficiency under stress conditions, which largely contributes to increased growth and biomass accumulation. Studies relating to exogenous BRs reveal a high dependency on concentrations with regards to BR effects on plants. Genetic studies show a positive correlation between the endogenous BR levels and abiotic stress tolerance, although this assumption contradicts with the performance of some BR mutants under stress conditions. Notably, plant responses to BRs greatly vary depending on the plant species, developmental stages, and environmental conditions. In addition, other hormones and signaling molecules that participate in fine-tuning the BRs effects also play an important role in plant adaptation to stress. Here, we review the involvement of BRs in plant responses to abiotic stresses. We also discuss available literature to show potential mechanisms of BR-induced abiotic stress tolerance. These studies signify the complexity of BR action in mediating stress responses in plants.

The Rice Basic Helix-Loop-Helix 79 (OsbHLH079) Determines Leaf Angle and Grain Shape.

Changes in plant architecture, such as leaf size, leaf shape, leaf angle, plant height, and floral organs, have been major factors in improving the yield of cereal crops. Moreover, changes in grain size and weight can also increase yield. Therefore, screens for additional factors affecting plant architecture and grain morphology may enable additional improvements in yield. Among the basic Helix-Loop-Helix (bHLH) transcription factors in rice (Oryza sativa), we found an enhancer-trap T-DNA insertion mutant of OsbHLH079 (termed osbhlh079-D). The osbhlh079-D mutant showed a wide leaf angle phenotype and produced long grains, similar to the phenotypes of mutants with increased brassinosteroid (BR) levels or enhanced BR signaling. Reverse transcription-quantitative PCR analysis showed that BR signaling-associated genes are largely upregulated in osbhlh079-D, but BR biosynthesis-associated genes are not upregulated, compared with its parental japonica cultivar ‘Dongjin’. Consistent with this, osbhlh079-D was hypersensitive to BR treatment. Scanning electron microscopy revealed that the expansion of cell size in the adaxial side of the lamina joint was responsible for the increase in leaf angle in osbhlh079-D. The expression of cell-elongation-associated genes encoding expansins and xyloglucan endotransglycosylases/hydrolases increased in the lamina joints of leaves in osbhlh079-D. The regulatory function of OsbHLH079 was further confirmed by analyzing 35S::OsbHLH079 overexpression and 35S::RNAi-OsbHLH079 gene silencing lines. The 35S::OsbHLH079 plants showed similar phenotypes to osbhlh079-D, and the 35S::RNAi-OsbHLH079 plants displayed opposite phenotypes to osbhlh079-D. Taking these observations together, we propose that OsbHLH079 functions as a positive regulator of BR signaling in rice.

Response of brassinosteroids to nitrogen rates and their regulation on rice spikelet degeneration during meiosis

AbstractThe plant steroid hormones brassinosteroids (BRs) play pivotal roles in modulating flower and fruit production. Nitrogen (N) is a key factor affecting rice (Oryza sativa L.) production. We hypothesized that BRs would respond to N application rates at spikelet differentiation (SD) and regulate spikelet degeneration in rice. Three rice cultivars were field‐grown and treated with five N rates at SD. Plant N and BRs contents, antioxidant capacity, and energy status were observed during meiosis in young panicles, and their relationships with spikelet degeneration were evaluated. In all the N treatments, the BRs, adenosine triphosphate, and energy charge levels, activities of the enzymes involved in energy metabolism, including cytochrome C oxidase and succinate dehydrogenase, total antioxidant capacity, and grain yield, were the highest, whereas hydrogen peroxide (H2O2) content and vacuolar processing enzymes (VPE) genes expression levels, and spikelet degeneration rate were the lowest when plant N content was 2.6% during meiosis. The rice BRs‐deficient mutants showed substantial reduction in BRs levels, antioxidant capacity, and energy status, but great increase in H2O2 content, VPE genes expression levels, and spikelet degeneration rate than the wild type (WT); moreover, these parameters in WT panicles could be regulated, whereas in BRs‐deficient mutant panicles, they were not distinctly affected by N application. The results indicated that BRs mediate the effects of N rates on spikelet degeneration, and elevated BRs levels in rice panicles effectively inhibit spikelet degeneration when plant N content is 2.6% during meiosis by elevating antioxidant capacity and energy status.

Brassinosteroid overproduction improves lignocellulose quantity and quality to maximize bioethanol yield under green-like biomass process in transgenic poplar

BackgroundAs a leading biomass feedstock, poplar plants provide enormous lignocellulose resource convertible for biofuels and bio-chemicals. However, lignocellulose recalcitrance particularly in wood plants, basically causes a costly bioethanol production unacceptable for commercial marketing with potential secondary pollution to the environment. Therefore, it becomes important to reduce lignocellulose recalcitrance by genetic modification of plant cell walls, and meanwhile to establish advanced biomass process technology in woody plants. Brassinosteroids, plant-specific steroid hormones, are considered to participate in plant growth and development for biomass production, but little has been reported about brassinosteroids roles in plant cell wall assembly and modification. In this study, we generated transgenic poplar plant that overexpressed DEETIOLATED2 gene for brassinosteroids overproduction. We then detected cell wall feature alteration and examined biomass enzymatic saccharification for bioethanol production under various chemical pretreatments.ResultsCompared with wild type, the PtoDET2 overexpressed transgenic plants contained much higher brassinosteroids levels. The transgenic poplar also exhibited significantly enhanced plant growth rate and biomass yield by increasing xylem development and cell wall polymer deposition. Meanwhile, the transgenic plants showed significantly improved lignocellulose features such as reduced cellulose crystalline index and degree of polymerization values and decreased hemicellulose xylose/arabinose ratio for raised biomass porosity and accessibility, which led to integrated enhancement on biomass enzymatic saccharification and bioethanol yield under various chemical pretreatments. In contrast, the CRISPR/Cas9-generated mutation of PtoDET2 showed significantly lower brassinosteroids level for reduced biomass saccharification and bioethanol yield, compared to the wild type. Notably, the optimal green-like pretreatment could even achieve the highest bioethanol yield by effective lignin extraction in the transgenic plant. Hence, this study proposed a mechanistic model elucidating how brassinosteroid regulates cell wall modification for reduced lignocellulose recalcitrance and increased biomass porosity and accessibility for high bioethanol production.ConclusionsThis study has demonstrated a powerful strategy to enhance cellulosic bioethanol production by regulating brassinosteroid biosynthesis for reducing lignocellulose recalcitrance in the transgenic poplar plants. It has also provided a green-like process for biomass pretreatment and enzymatic saccharification in poplar and beyond.

DcBAS1, a Carrot Brassinosteroid Catabolism Gene, Modulates Cellulose Synthesis.

Brassinosteroids (BRs) are important phytohormones and play critical roles during the growth and development of the plant. Numerous studies on biosynthesis and the signaling pathway of BRs have been performed, while the report about the metabolism of BRs is limited to carrots. In this study, we identified a homologous gene of AtCYP734A1/BAS1 (DCAR_009214), named DcBAS1, from carrots based on the data of the genome. The Arabidopsis overexpression line hosting the DcBAS1 gene was a dwarf and had crinkled blades and shortened petioles. Exogenous BL treatment rescued its growth and stem elongation. In addition, overexpressing DcBAS1 inhibited the cellulose synthesis in transgenic Arabidopsis plants. Results of quantitative real-time polymerase chain reaction revealed that overexpression of DcBAS1 inhibited the expression levels of AtCESAs genes (AtCESA1, AtCESA3, and AtCESA6), which are involved in cellulose synthesis in primary cell walls. AtBES1, which can be active by BR signaling, was also inhibited. These results revealed that DcBAS1 is the important gene involved in BR metabolism in carrots. Overexpression of DcBAS1 reduced the level of endogenous BRs and inhibited the cellulose synthesis in transgenic Arabidopsis plants.

Melatonin Deficiency Confers Tolerance to Multiple Abiotic Stresses in Rice via Decreased Brassinosteroid Levels.

Melatonin has long been recognized as a positive signaling molecule and potent antioxidant in plants, which alleviates damage caused by adverse conditions such as salt, cold, and heat stress. In this study, we found a paradoxical role for melatonin in abiotic stress responses. Suppression of the serotonin N-acetyltransferase 2 (snat2) gene encoding the penultimate enzyme in melatonin biosynthesis led to simultaneous decreases in both melatonin and brassinosteroid (BR) levels, causing a semi-dwarf with erect leaf phenotype, typical of BR deficiency. Here, we further characterized snat2 rice in terms of grain morphology and abiotic stress tolerance, to determine whether snat2 rice exhibited characteristics similar to those of BR-deficient rice. As expected, the snat2 rice exhibited tolerance to multiple stress conditions including cadmium, salt, cold, and heat, as evidenced by decreased malondialdehyde (MDA) levels and increased chlorophyll levels, in contrast with SNAT2 overexpression lines, which were less tolerant to stress than wild type plants. In addition, the length and width of grain from snat2 plants were reduced relative to the wild type, which is reminiscent of BR deficiency in rice. Other melatonin-deficient mutant rice lines with suppressed BR synthesis (i.e., comt and t5h) also showed tolerance to salt and heat stress, whereas melatonin-deficient rice seedlings without decreased BR levels (i.e., tdc) failed to exhibit increased stress tolerance, suggesting that stress tolerance was increased not by melatonin deficiency alone, but by a melatonin deficiency-mediated decrease in BR.

Hypocotyl Elongation Inhibition of Melatonin Is Involved in Repressing Brassinosteroid Biosynthesis in Arabidopsis.

Melatonin functions as a plant hormone/regulator in the regulation of growth and development. However, the underlying mechanisms are still unclear. In this study, we found that a high dose of melatonin inhibited hypocotyl elongation in a dose-dependent manner in Arabidopsis. An expression profile analysis showed that hypocotyl growth inhibition by melatonin was involved in reprograming the expression of cell elongation genes and brassinosteroid (BRs) biosynthetic genes. Furthermore, similar to BR biosynthetic inhibitor brassinazole (BRZ), a high concentration of melatonin upregulated BR-biosynthetic genes and downregulated BR-induced genes involved in cell elongation, while melatonin was inefficient in brassinazole-resistant mutants like the bzr1-1D and bes1-D in hypocotyl inhibition. The comparative expression profile analysis showed an opposite expression mode in the co-regulated genes between melatonin and BZR1 or melatonin and brassinolide (BL). Additionally, exogenous BL rescued the repressive phenotype of BR biosynthesis-deficient mutant like det2-1 even in the presence of high-dose melatonin, but not BR receptor mutant bri1-5 or signal transduction mutant bin2-1. A biochemical analysis further confirmed that melatonin reduced endogenous BR levels in a dose-dependent manner in Arabidopsis. Taken together, these results indicate that melatonin inhibits BR biosynthesis but does not block BR signaling in the inhibition of hypocotyl elongation and extends insights on the role of melatonin in cross-talking with plant hormone signaling.

Brassinosteroids mediate the effect of soil-drying during meiosis on spikelet degeneration in rice

This study investigated whether and how brassinosteroids (BRs) mediate the effect of soil-drying during meiosis on spikelet degeneration in rice (Oryza sativa L.). A field-grown rice cultivar was exposed to three soil moisture treatments during meiosis: well-watered (WW), moderate soil-drying (MD) and severe soil-drying (SD). Compared with the WW treatment, the MD treatment enhanced BRs biosynthesis, reduced spikelet degeneration, and increased grain yield. The SD treatment had the opposite effects. Changes in the levels of adenosine triphosphate (ATP), energy charge, activities of enzymes involved in energy metabolism, including cytochrome C oxidase (CCO) and succinate dehydrogenase (SDH), and total antioxidant capacity (T-AOC) were consistent with those in BRs levels, whereas the hydrogen peroxide (H2O2) content, vacuolar processing enzyme genes (OsVPE2 and OsVPE3) expression levels and the degree of nuclear DNA fragmentation showed the opposite trend. Knockdown of the BRs synthesis gene OsD11 or application of a BRs biosynthesis inhibitor to young panicles vastly decreased the BRs and ATP contents, energy charge, CCO and SDH activities, and T-AOC in young panicles but increased the H2O2 content, OsVPE2 and OsVPE3 expression, and spikelet degeneration compared to the control, and the opposite effects were observed when exogenous BRs were applied. Therefore, BRs likely mediate the effect of soil-drying on spikelet degeneration, and elevated BRs levels in rice panicles inhibit spikelet degeneration under moderate soil-drying during meiosis by elevating antioxidant capacity and energy status.

Brassinosteroids enhance cold tolerance in Elymus nutans via mediating redox homeostasis and proline biosynthesis

Brassinosteroids (BRs) are a class of polyhydroxylated steroidal phytohormones that induce plant tolerance to a wide variety of stresses. Cold stress is a major environmental factor that limits plant growth. However, the mechanisms by which BRs regulate cold tolerance in alpine plants remains unclear. We analyzed the effects of 24-epibrassinolide (EBR) on growth, antioxidant defense, proline metabolism, and cold stress-related genes in Elymus nutans seedlings exposed to cold stress. Cold stress increased the transcript levels of BR-biosynthetic genes and the endogenous levels of BRs in E. nutans, which indicates the role of BRs in regulating cold tolerance. In addition, cold stress inhibited plant growth and increased malondialdehyde and reactive oxygen species (ROS) accumulation. However, application of EBR (1 μM) triggered catalase (CAT) activity and ascorbate (AsA)-reduced glutathione (GSH) cycle, thereby leading to lower ROS levels and plant growth inhibition. BR-induced cold tolerance was associated with an increase in proline levels. Pretreatment with EBR prior to cold stress improved the activities of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and Δ1-pyrroline-5-carboxylate reductase (P5CR), while slightly reduced the activities of proline dehydrogenase (PDH) and Δ1-pyrroline-5-carboxylate dehydrogenase (P5CDH). Increased transcript levels of P5CS and P5CR genes and decreased transcript level of PDH1 were detected in EBR-pretreated seedlings. Exogenous proline could alleviate the plant damage caused by cold stress in E. nutans and Arabidopsis bak1 mutant. Furthermore, bak1 mutant accumulated less proline compared with wild type plants, which indicates the close association between BR-mediated cold tolerance and proline metabolism. EBR Pretreatment also induced the expression of cold stress-related genes. These findings suggest that BRs enhance cold tolerance by inducing cold stress-related genes, which further regulates antioxidant defense and proline accumulation.

Brassinosteroid regulation of wood formation in poplar.

Brassinosteroids have been implicated in the differentiation of vascular cell types in herbaceous plants, but their roles during secondary growth and wood formation are not well defined. Here we pharmacologically and genetically manipulated brassinosteroid levels in poplar trees and assayed the effects on secondary growth and wood formation, and on gene expression within stems. Elevated brassinosteroid levels resulted in increases in secondary growth and tension wood formation, while inhibition of brassinosteroid synthesis resulted in decreased growth and secondary vascular differentiation. Analysis of gene expression showed that brassinosteroid action is positively associated with genes involved in cell differentiation and cell-wall biosynthesis. The results presented here show that brassinosteroids play a foundational role in the regulation of secondary growth and wood formation, in part through the regulation of cell differentiation and secondary cell wall biosynthesis.