The F-box Protein KIB1 Mediates Brassinosteroid-Induced Inactivation and Degradation of GSK3-like Kinases in Arabidopsis

The glycogen synthase kinase-3 (GSK3) family kinases are central cellular regulators highly conserved in all eukaryotes. In Arabidopsis, the GSK3-like kinase BIN2 phosphorylates a range of proteins to control broad developmental processes, and BIN2 is degraded through unknown mechanism upon receptor kinase-mediated brassinosteroid (BR) signaling. Here we identify KIB1 as an F-box E3 ubiquitin ligase that promotes the degradation of BIN2 while blocking its substrate access. Loss-of-function mutations of KIB1 and its homologs abolished BR-induced BIN2 degradation and caused severe BR-insensitive phenotypes. KIB1 directly interacted with BIN2 in a BR-dependent manner and promoted BIN2 ubiquitination in vitro. Expression of an F-box-truncated KIB1 caused BIN2 accumulation but dephosphorylation of its substrate BZR1 and activation of BR responses because KIB1 blocked BIN2 binding to BZR1. Our study demonstrates that KIB1 plays an essential role in BR signaling by inhibiting BIN2 through dual mechanisms of blocking substrate access and promoting degradation.

Characterization of synthetic ecdysteroid analogues as functional mimics of brassinosteroids in plant growth

Brassinosteroids (BRs) are plant steroidal hormones that play important roles in many stages of plant growth. Several plant species produce ecdysteroids, which are known as insect molting steroid hormones. In this study, we evaluated the biological activities of three hydroxysteroidal compounds, 20-hydroxyecdysone (ECD), 7,8-dihydro-8α-20-hydroxyecdysone (DHECD), and 7,8-dihydro-5α,8α-20-hydroxyecdysone (α-DHECD), and compared their activities with that of brassinolide (BL), the most potent BR. In rice, DHECD and α-DHECD enhanced the degree of lamina inclination, as do BRs. In Arabidopsis thaliana, DHECD and α-DHECD increased hypocotyl length in the wild-type, and also partially overcame the hypocotyl shortening in the wild-type caused by 0.3μM brassinazole, a specific BR biosynthesis inhibitor. DHECD and α-DHECD partially reduced dwarfism in the BR-biosynthesis-deficient mutant det2. Treatment with DHECD or α-DHECD downregulated the expression of the BR biosynthesis genes DWF4 and CPD, which are generally, suppressed by BR, and upregulated the expression of TCH4 and SAUR-AC1, which are generally promoted by BR. However, their regulated activities were less effective than BL. Moreover, the 10^-4M DHECD and α-DHECD induced the accumulation of dephosphorylated BIL1/BZR1 that enhanced BR signaling as a master transcription factor. In contrast, ECD did not affect rice lamina bending, Arabidopsis hypocotyl elongation, the expression levels of BR-related genes and BIL1/BZR1 phosphorylation status. Based on these results, we hypothesize that both DHECD and α-DHECD have functional activities similar to those of BR.

A mutant in the CsDET2 gene leads to a systemic brassinosteriod deficiency and super compact phenotype in cucumber (Cucumis sativus L.)

A novel dwarf cucumber mutant, scp-2, displays a typical BR biosynthesis-deficient phenotype, which is due to a mutation in CsDET2 for a steroid 5-alpha-reductase. Brassinosteroids (BRs) are a group of plant hormones that play important roles in the development of plant architecture, and extreme dwarfism is a typical outcome of BR-deficiency. Most cucumber (Cucumis sativus L.) varieties have an indeterminate growth habit, and dwarfism may have its value in manipulation of plant architecture and improve production in certain production systems. In this study, we identified a spontaneous dwarf mutant, super compact-2 (scp-2), that also has dark green, wrinkle leaves. Genetic analyses indicated that scp-2 was different from two previously reported dwarf mutants: compact (cp) and super compact-1 (scp-1). Map-based cloning revealed that the mutant phenotype was due to two single nucleotide polymorphism and a single-base insertion in the CsDET2 gene that resulted in a missense mutation in a conserved amino acid and thus a truncated protein lacking the conserved catalytic domains in the predicted steroid 5α-reductase protein. Measurement of endogenous hormone levels indicated a reduced level of brassinolide (BL, a bioactive BR) in scp-2, and the mutant phenotype could be partially rescued by the application of epibrassinolide (EBR). In addition, scp-2 mutant seedlings exhibited dark-grown de-etiolation, and defects in cell elongation and vascular development. These data support that scp-2 is a BR biosynthesis-deficient mutant, and that the CsDET2 gene plays a key role in BR biosynthesis in cucumber. We also described the systemic BR responses and discussed the specific BR-related phenotypes in cucumber plants.

Scanning for New BRI1 Mutations via TILLING Analysis

The identification and characterization of a mutational spectrum for a specific protein can help to elucidate its detailed cellular functions. BRASSINOSTEROID INSENSITIVE1 (BRI1), a multidomain transmembrane receptor-like kinase, is a major receptor of brassinosteroids in Arabidopsis (Arabidopsis thaliana). Within the last two decades, over 20 different bri1 mutant alleles have been identified, which helped to determine the significance of each domain within BRI1. To further understand the molecular mechanisms of BRI1, we tried to identify additional alleles via targeted induced local lesions in genomes. Here, we report our identification of 83 new point mutations in BRI1, including nine mutations that exhibit an allelic series of typical bri1 phenotypes, from subtle to severe morphological alterations. We carried out biochemical analyses to investigate possible mechanisms of these mutations in affecting brassinosteroid signaling. A number of interesting mutations have been isolated via this study. For example, bri1-702, the only weak allele identified so far with a mutation in the activation loop, showed reduced autophosphorylation activity. bri1-705, a subtle allele with a mutation in the extracellular portion, disrupts the interaction of BRI1 with its ligand brassinolide and coreceptor BRI1-ASSOCIATED RECEPTOR KINASE1. bri1-706, with a mutation in the extracellular portion, is a subtle defective mutant. Surprisingly, root inhibition analysis indicated that it is largely insensitive to exogenous brassinolide treatment. In this study, we found that bri1-301 possesses kinase activity in vivo, clarifying a previous report arguing that kinase activity may not be necessary for the function of BRI1. These data provide additional insights into our understanding of the early events in the brassinosteroid signaling pathway.

Electron Paramagnetic Resonance (EPR) Spectroscopy in Studies of the Protective Effects of 24-Epibrasinoide and Selenium against Zearalenone-Stimulation of the Oxidative Stress in Germinating Grains of Wheat

These studies concentrate on the possibility of using selenium ions and/or 24-epibrassinolide at non-toxic levels as protectors of wheat plants against zearalenone, which is a common and widespread mycotoxin. Analysis using the UHPLC-MS technique allowed for identification of grains having the stress-tolerant and stress-sensitive wheat genotype. When germinating in the presence of 30 µM of zearalenone, this mycotoxin can accumulate in both grains and hypocotyls germinating from these grains. Selenium ions (10 µM) and 24-epibrassinolide (0.1 µM) introduced together with zearalenone decreased the uptake of zearalenone from about 295 to 200 ng/g and from about 350 to 300 ng/g in the grains of tolerant and sensitive genotypes, respectively. As a consequence, this also resulted in a reduction in the uptake of zearalenone from about 100 to 80 ng/g and from about 155 to 128 ng/g in the hypocotyls from the germinated grains of tolerant and sensitive wheat, respectively. In the mechanism of protection against the zearalenone-induced oxidative stress, the antioxidative enzymes-mainly superoxide dismutase (SOD) and catalase (CAT)-were engaged, especially in the sensitive genotype. Electron paramagnetic resonance (EPR) studies allowed for a description of the chemical character of the long-lived organic radicals formed in biomolecular structures which are able to stabilize electrons released from reactive oxygen species as well as the changes in the status of transition paramagnetic metal ions. The presence of zearalenone drastically decreased the amount of paramagnetic metal ions-mainly Mn(II) and Fe(III)-bonded in the organic matrix. This effect was particularly found in the sensitive genotype, in which these species were found at a smaller level. The protective effect of selenium ions and 24-epibrassinolide originated from their ability to inhibit the destruction of biomolecules by reactive oxygen species. An increased ability to defend biomolecules against zearalenone action was observed for 24-epibrassinolide.

Role of brassinosteroids in alleviating toxin-induced stress of Verticillium dahliae on cotton callus growth

Brassinosteroids are well known to mitigate biotic stresses; however, their role to induce tolerance against Verticillium dahliae is unknown. The current study employed V. dahliae (Vd) toxin as pathogen-free model system to induce stress on cotton callus growth, and its amelioration was investigated using 24-epibrassinolide (EBR). Results revealed that EBR has ameliorative effects against Vd toxin with greater seen effect when callus was treated with EBR prior to its exposure to Vd toxin (pre-EBR treatment) than EBR applied along with Vd toxin simultaneously (co-EBR treatment). Pre-EBR-treated calli remained green, while 65 and 90% callus browning was observed in co-EBR- and Vd toxin-alone-treated callus, respectively. Likewise, the fresh weight of the pre-EBR-treated callus was 52% higher than Vd toxin-alone treatment, whereas this increase was only 23% in co-EBR-treated callus. Meanwhile, EBR treatment of the cotton callus has also increased the contents of chlorophylls a and b, carotenoids, total phenols, flavonoids, soluble sugars, and proteins and increased the activity of enzymes involved in secondary metabolism like polyphenol oxidase (PPO), phenylalanine ammonialyase (PAL), cinnamyl alchol dehydrogenase (CAD), and shikimate dehydrogenase (SKDH) over Vd toxin-alone treatment with higher increments being observed in pre-EBR-treated callus. Furthermore, EBR treatment mimicked the DNA damage and improved the structure of mitochondria, granum, stroma thylakoids, and the attachment of ribosomes with the endoplasmic reticulum. This EBR-mediated mitigation was primarily associated with substantially increased contents of photosynthetic pigments and regulation of secondary metabolism.

Exogenously Applied 24-Epibrassinolide (EBL) Ameliorates Detrimental Effects of Salinity by Reducing K+ Efflux via Depolarization-Activated K+ Channels

This study has investigated mechanisms conferring beneficial effects of exogenous application of 24-epibrassinolides (EBL) on plant growth and performance under saline conditions. Barley seedlings treated with 0.25 mg l-1 EBL showed significant improvements in root hair length, shoot length, shoot fresh weight and relative water content when grown in the presence of 150 mM NaCl in the growth medium. In addition, EBL treatment significantly decreased the Na+ content in both shoots (by approximately 50%) and roots. Electrophysiological experiments revealed that pre-treatment with EBL for 1 and 24 h suppressed or completely prevented the NaCl-induced K+ leak in the elongation zone of barley roots, but did not affect root sensitivity to oxidative stress. Further experiments using Arabidopsis loss-of-function gork1-1 (lacking functional depolarization-activated outward-rectifying K+ channels in the root epidermal cells) and akt1 (lacking inward-rectifying K+ uptake channel) mutants showed that NaCl-induced K+ loss in the elongation zone of roots was reduced by EBL pre-treatment 50- to 100-fold in wild-type Col-0 and akt1, but only 10-fold in the gork1-1 mutant. At the same time, EBL treatment shifted vanadate-sensitive H+ flux towards net efflux. Taken together, these data indicate that exogenous application of EBL effectively improves plant salinity tolerance by prevention of K+ loss via regulating depolarization-activated K+ channels.

Effects of 24-epibrassinolide and green light on plastid gene transcription and cytokinin content of barley leaves

In order to evaluate whether brassinosteroids (BS) and green light regulate the transcription of plastid genes in a cross-talk with cytokinins (CKs), transcription rates of 12 plastid genes (ndhF, rrn23, rpoB, psaA, psaB, rrn16, psbA, psbD, psbK, rbcL, atpB, and trnE/trnY) as well as the accumulation of transcripts of some photoreceptors (PHYA, CRY2, CRY1A, and CRY1B) and signaling (SERK and CAS) genes were followed in detached etiolated barley leaves exposed to darkness, green or white light ±1μm 24-epibrassinolide (EBL). EBL in the dark was shown to up-regulate the transcription of 12 plastid genes, while green light activated 10 genes and the EBL combined with the green light affected the transcription of only two genes (psaB and rpoB). Green light inhibited the expression of photoreceptor genes, except for CRY1A. Under the green light, EBL practically did not affect the expression of CRY1A, CAS and SERK genes, but it reduced the influence of white light on the accumulation of CAS, CRY1A, CRY1B, and SERK gene transcripts. The total content of BS in the dark and under white light remained largely unchanged, while under green light the total content of BRs (brassinolide, castasterone, and 6-deoxocastasterone) and HBRs (28-homobrassinolide, 28-homocastasterone, and 6-deoxo-28-homocastasterone) increased. The EBL-dependent up-regulation of plastome transcription in the dark was accompanied by a significant decrease in CK deactivation by O-glucosylation. However, no significant effect on the content of active CKs was detected. EBL combined with green light moderately increased the contents of trans-zeatin and isopentenyladenine, but had a negative effect on cis-zeatin. The most significant promotive effect of EBL on active CK bases was observed in white light. The data obtained suggest the involvement of CKs in the BS- and light-dependent transcription regulation of plastid genes.

Arsenic-induced genotoxic responses and their amelioration by diphenylene iodonium, 24-epibrassinolide and proline in Glycine max L

Presence of the toxic metalloid, "arsenic (As)" is ubiquitous in the environment especially in the soil and water. Its excess availability in the soil retards growth and metabolism of plants via (a) slowing down the cell division/elongation, (b) overproduction of reactive oxygen species (ROS), (c) modulation of antioxidant enzymes, and (d) alteration of DNA profile/genomic template stability (GTS). In the current study, diphenylene iodonium (DPI), 24-epibrassinolide (EBL) and proline (Pro) were used to analyze their roles in eliminating the adverse effects of As. Glycine max L. (variety JS 335) seeds were subjected to As (75 μM, Sodium arsenite was used as source of As), and in combination with DPI (10 μM), EBL (0.5 μM) or Pro (10 mM), for five consecutive days, and effects of these treatment combinations were analyzed on germination percentage, biomass, membrane stability, GTS and expressions of defensive genes. In addition, the levels of As, ROS, malondialdehyde, DNA content, oxidation, fragmentation, polymorphism, DNase activity, endogenous Pro and pyrroline-5-carboxylate synthetase activity were evaluated. The results indicated that the treatments of DPI, EBL or Pro are capable to alleviate detrimental effects of As, gauged from above variables, but with different magnitudes. Apropos As-stress mitigation, Pro was found to be the most effective under the confines of the study protocol. This study certainly provides new ideas for intensifying studies to unravel elusive central mechanism of amelioration involving use of DPI, EBL or Pro in plants with confirmed As-toxicity.

24-epibrassinolide stimulates imidacloprid detoxification by modulating the gene expression of Brassica juncea L

BACKGROUND

Pesticides cause oxidative stress to plants and their residues persist in plant parts, which are a major concern for the environment as well as human health. Brassinosteroids (BRs) are known to protect plants from abiotic stress conditions including pesticide toxicity. The present study demonstrated the effects of seed-soaking with 24-epibrassinolide (EBR) on physiological responses of 10-day old Brassica juncea seedlings grown under imidacloprid (IMI) toxicity.

RESULTS

In the seedlings raised from EBR-treated seeds and grown under IMI toxicity, the contents of hydrogen peroxide (H₂O₂) and superoxide anion (O^.₂^-) were decreased, accompanied by enhanced activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione-S-transferase (GST), guaiacol peroxidase (POD) and the content of glutathione (GSH). As compared to controls, the gene expressions of SOD, CAT, GR, POD, NADH (NADH-ubiquinone oxidoreductase), CXE (carboxylesterase), GSH-S (glutathione synthase), GSH-T (glutathione transporter-1), P450 (cytochrome P450 monooxygenase) and GST1-3,5-6 were enhanced in the seedlings raised from EBR-treated seeds and grown in IMI supplemented substratum. However, expression of RBO (respiratory burst oxidase, the gene responsible for H₂O₂ production) was decreased in seedlings raised from EBR treated seeds and grown under IMI toxicity. Further, the EBR seed treatment decreased IMI residues by more than 38% in B. juncea seedlings.

CONCLUSIONS

The present study revealed that EBR seed soaking can efficiently reduce oxidative stress and IMI residues by modulating the gene expression of B. juncea under IMI stress. In conclusion, exogenous EBR application can protect plants from pesticide phytotoxicity.

Dwarf and short grain 1, encoding a putative U-box protein regulates cell division and elongation in rice

Plant hormones coordinate a plant's responses to environmental stimuli and the endogenous developmental programs for cell division and elongation. Brassinosteroids are among the most important of these hormones in plant development. Recently, the ubiquitin-26S-proteasome system was identified to play a key role in hormone biology. In this study, we analyzed the function of a rice (Oryza sativa) gene, DSG1, which encodes a U-box E3 ubiquitin ligase. In the dsg1 mutant (an allelic mutant of tud1), the lengths of the roots, internodes, panicles, and seeds were shorter than that in the wild-type, which was due to defects in cell division and elongation. In addition, the leaves of the dsg1 mutant were wider and curled. The DSG1 protein is nuclear- and cytoplasm-localized and does not show tissue specificity in terms of its expression, which occurs in roots, culms, leaves, sheaths, and spikelets. The dsg1 mutant is less sensitive to brassinosteroid treatment than the wild-type, and DSG1 expression is negatively regulated by brassinosteroids, ethylene, auxin, and salicylic acid. These results demonstrate that DSG1 positively regulates cell division and elongation and may be involved in multiple hormone pathways.

Methods for Modeling Brassinosteroid-Mediated Signaling in Plant Development

Mathematical modeling of biological processes is a useful tool to draw conclusions that are contained in the data, but not directly reachable, as well as to make predictions and select the most efficient follow-up experiments. Here we outline a method to model systems of a few proteins that interact transcriptionally and/or posttranscriptionally, by representing the system as Ordinary Differential Equations and to study the model dynamics and stationary states. We exemplify this method by focusing on the regulation by the brassinosteroid (BR) signaling component BRASSINOSTEROID INSENSITIVE1 ETHYL METHYL SULFONATE SUPPRESSOR1 (BES1) of BRAVO, a quiescence-regulating transcription factor expressed in the quiescent cells of Arabidopsis thaliana roots. The method to extract the stationary states and the dynamics is provided as a Mathematica code and requires basic knowledge of the Mathematica software to be executed.

Brassinosteroid-induced changes of lipid composition in leaves of Pisum sativum L. during senescence

The effect of steroid phytohormone 24-epibrassinolide (EBR) on the composition of some lipid classes (free fatty acids, triacylglycerols and galactolipids) in detached pea leaves was studied for the first time. EBR (0.1μM) promoted senescence and increased the content of 14:0, 16:0 and 18:1 free fatty acids as well as 18:2 and 18:3 bound to triacylglycerols in the detached leaves in contrast to mock-treated leaves. The content of all identified fatty acids bound to galactolipids decreased in the detached leaves treated with EBR compared to that in mock-treated leaves. These findings suggest that free fatty acids are liberated from polar lipids and then undergo esterification to neutral lipids in the detached leaves upon EBR treatment. We propose that steroid phytohormones may be involved into regulation of leaf senescence via alteration of cell lipid composition.

Quantitation of Cell Type-Specific Responses to Brassinosteroid by Deep Sequencing of Polysome-Associated Polyadenylated RNA

Hormonal signaling pathways control almost every aspect of plant physiology and development. Extensive analysis of hormonal signaling output, i.e., gene expression, has therefore been the focus of many studies. These analyses have been primarily conducted on total extracts derived from a mixture of tissues and cell types, consequentially limiting delineation of precise models. In this chapter, methods for tissue-specific functional genomics are overviewed, in which hormonal responses are analyzed at the transcriptional and the translational levels. Deep sequencing of polysome-associated polyadenylated RNA is employed for cell type-specific quantitation of translatome responses to brassinosteroids. Polysomes are purified by the previously established Translating Ribosome Affinity Purification (TRAP) method, in which the expression of a tagged ribosomal protein is targeted to the tissue of interest, allowing tissue-specific immunopurification of the polysome complexes. The methods presented assess establishment and selection of suitable transgenic lines. A protocol for hormonal treatment of the Arabidopsis thaliana root as a case study, TRAP and linear amplification of the purified polysome-associated polyadenylated RNA are described. Finally, a step-by-step presentation is included of the analysis of the RNA deep-sequencing data and Rscript for plotting hierarchically clustered heatmap of the expressed genes.

A Technical Framework for Studying the Signaling Nexus of Brassinosteroids and Immunity

Pathway cross-communication cannot be simply tackled by studying isolated signaling systems. Yet understanding how signal transduction pathways attenuate or reinforce each other in vivo is a challenging task. In plants, biosynthesis and signaling of brassinosteroids (BRs) finely regulate growth and defense programs through a complex array of mechanistic and physiological interactions. Conversely, induction of defenses also impacts on the BR biosynthesis at the transcriptional level. In this chapter, we present an experimental framework to study the physiological connection between BR-controlled growth and defenses. We focus on the signaling pathways regulated by the two archetypal cell surface receptors, BRASSINOSTEROID INSENSITIVE1 (BRI1) and FLAGELLIN-SENSITIVE2 (FLS2), to illustrate the signaling nexus of BRs and plant immunity. In Arabidopsis thaliana, these pathways provide one of the very few systems in which the tools and mechanistic details exist to study cross talk at the molecular level.

Effect of 24-epibrassinolide on Brassica napus alternative respiratory pathway, guard cells movements and phospholipid signaling under salt stress

Using Brassica napus roots we observed statistically significant increase in alternative respiratory pathway in response to exogenous 24-epibrassinolide (EBL) under optimal conditions and salinity. Also we observed activation of phospholipid signaling under the same conditions in response to EBL by measuring levels of lipid second messengers - diacylglycerol (DAG) and phosphatidic acid (PA). We found that brassinosteroids cause closure of stomata in isolated leaf disks while inhibitors of alternative oxidase cancelled these effects. This study demonstrates that BRs activate total respiration rate, alternative respiratory pathway, production of PA and DAG, stimulate stomata closure and growth under optimal conditions and salinity. Also, specific inhibitor of brassinosteroids biosynthesis decreased alternative respiratory pathway and production of lipid messengers in rape plants.

Brassinosteroid Action in Plant Abiotic Stress Tolerance

Brassinosteroids (BRs) are a class of plant steroidal hormones that play essential roles in plant growth and development. Systematic studies had first been undertaken concomitantly to determine both the effects of exogenous BR on stress phenotypes of Arabidopsis thaliana and Brassica napus (rapeseed) seedlings and the expression of stress marker genes in BR-treated and untreated seedlings. When reproducible and convincing evidence of the role of BR in stress tolerance had been obtained, molecular mechanisms underlying the ability of BR to confer tolerance against heat, cold, drought, and salt stress, as well as pathogen resistance were studied with several molecular approaches and tools. The results of these studies have together provided valuable insights into how BRs, through their control of many basic cellular processes and stress responses, promote vigor in plants and prepare the plant to mount a dynamic response upon environmental challenges. Protocols to assess BR effects on abiotic stress tolerance in Arabidopsis and rapeseed seedlings are described here and they can be fine-tuned and adapted for other plant species.

Evaluation of heterocyclic steroids and curcumin derivatives as anti-breast cancer agents: Studying the effect on apoptosis in MCF-7 breast cancer cells

Anticancer agents consisting of hybrid molecules are used to improve effectiveness and diminish drug resistance. The current study aimed to introduce newly synthesized hetero-steroids of promising anticancer effects. Besides, the pro-apoptotic effects of new compounds were investigated extensively. Several pyrimidino-, triazolopyrimidino-, pyridazino-, and curcumin-steroid derivatives were synthesized, elucidated and confirmed using the spectral and analytical data. The synthesized hetero-steroids, compounds 9, 10, 11, 12, 13, 14, 15, 18, 20, 21, 22 and 24, were tested for their cytotoxic effects versus human breast cancer cells (MCF-7) using neutral red supravital dye uptake assay. Compound 24 (IC50=18μM) showed more inhibitory influence on MCF-7 growth. Using QRT-PCR (Quantitative real time-polymerase chain reaction), CCND1, Survivin, BCL-2, CDC2, P21 and P53, genes expression levels were investigated. The study results disclose that compounds 4, 7, 18, 24 knocked down the expression levels of CCND1, Survivin, BCL-2 and CDC2. However, P21 and P53 were up-regulated by compounds 21, 22. This study introduced promising pro-apoptotic anticancer agents acting through the modulation of key regulators of apoptosis and cell cycle genes.

Effect of seed pre-soaking with 24-epibrassinolide on growth and photosynthetic parameters of Brassica juncea L. in imidacloprid soil

Pesticides are widely used to protect crop plants from various insect pests. However, application of pesticides causes phytotoxicity to plants which results in their impaired growth and development. Brassinosteroids are well known to protect plants under abiotic stress conditions. The purpose of the present study was to access the ameliorative role of 24-epibrassinolide (EBR) in Brassica juncea L. under imidacloprid (IMI) toxicity. B. juncea plants were raised from seeds soaked in 0.1, 1 and 100nM of EBR, and grown in soils amended with 250, 300 and 350mgkg(-1) IMI pesticide, and observed for growth, pigments and photosynthetic parameters after 30, 60 and 90 days of seed sowing. The plants grown in soil treated with IMI exhibited a significant reduction in shoot length, number of leaves, chlorophyll contents and photosynthetic parameters like photosynthetic rate, stomatal conductance, inter-cellular CO2 and transpiration rate, when compared with their respective controls. However, pigments which act as antioxidants such as carotenoids, anthocyanins and xanthophylls were increased with IMI stress. Pre-sowing seed treatment with EBR decreased the toxic effects of IMI and increased the growth, pigment biosynthesis and photosynthetic parameters of the plants grown in IMI amended soil. Maximum increase in all the growth and photosynthetic parameters was noticed in plants raised from seeds treated with 100nM EBR and grown in IMI amended soil.

24-Epibrassinolide ameliorates salt stress effects in the symbiosis Medicago truncatula-Sinorhizobium meliloti and regulates the nodulation in cross-talk with polyamines

Brassinosteroids (BRs) are steroid plant hormones that have been shown to be involved in the response to salt stress in cross-talk with other plant growth regulators such as polyamines (PAs). In addition, BRs are involved in the regulation of the nodulation in the rhizobium-legume symbiosis through the alteration of the PAs content in leaves. In this work, we have studied the effect of exogenous 24-epibrassinolide (EBL) in the response to salinity of nitrogen fixation in the symbiosis Medicago truncatula-Sinorhizobium meliloti. Foliar spraying of EBL restored the growth of plants subjected to salt stress and provoked an increment of the nitrogenase activity. In general, PAs levels in leaves and nodules decreased by the salt and EBL treatments, however, the co-treatment with NaCl and EBL augmented the foliar spermine (Spm) concentration. This increment of the Spm levels was followed by a reduction of the membrane oxidative damage and a diminution of the proline accumulation. The effect of BRs on the symbiotic interaction was evaluated by the addition of 0.01, 0.1 and 0.5 μM EBL to the growing solution, which provoked a reduction of the nodule number and an increment of the PAs levels in shoot. In conclusion, foliar treatment with EBL had a protective effect against salt stress in the M. truncatula-S. meliloti symbiosis mediated by an increment of the Spm levels. Treatment of roots with EBL incremented PAs levels in shoot and reduced the nodule number which suggests a cross-talk between PAs and BRs in the nodule suppression and the protection against salt stress.

Involvement of dehydrins in 24-epibrassinolide-induced protection of wheat plants against drought stress

In this study, we performed a comparative analysis of the physiological and biochemical parameters of wheat cultivars with contrasting drought resistance, drought-resistant Omskaya 35 (O-35) and less drought-resistant Salavat Yulaev (SYu), during 7-day germination under drought stress simulated by 5% mannitol. In addition, we evaluated the effectiveness of pre-sowing seed treatment with 0.4 μM 24-epibrassinolide (EBR) used to increase the resistance of plants of both cultivars to drought stress. It was revealed that mannitol has caused significant changes in the hormonal balance of the plants of both cultivars, associated with abscisic acid (ABA) accumulation and decrease in the contents of indoleacetic acid (IAA) and cytokinins (CKs). It should be noted that more dramatic changes in the content of phytohormones were characteristic for seedlings of SYu cultivar, which was reflected in a stronger growth inhibition of these plants. Pretreatment with EBR mitigated the negative effect of drought on the hormonal status and growth of seedlings during their germination. Furthermore, we found that drought caused accumulation of dehydrin (DHN) proteins, especially of low molecular weight DHNs, whose abundance was 2.5 times greater in O-35 cultivar than in SYu plants. EBR-pretreated plants of both cultivars were characterized by the additional accumulation of DHNs, indicating their involvement in the development of the EBR-induced wheat drought resistance. The use of fluridone allowed us to demonstrate ABA-dependent and ABA-independent pathways of regulation of low molecular mass dehydrins accumulation by EBR in wheat plants of both cultivars under drought conditions.

The role of 24-epibrassinolide in the regulation of photosynthetic characteristics and nitrogen metabolism of tomato seedlings under a combined low temperature and weak light stress

In the present study, we aimed to investigate the effects of exogenous 24-epibrassinolide (EBR) on growth, photosynthetic characteristics, chlorophyll fluorescence imaging, and nitrogen metabolism of tomato leaves under low temperature and weak light conditions. The results showed that foliar application of EBR significantly alleviated the inhibition of plant growth, and increased the fresh and dry weights of tomato plants under a combined low temperature and weak light stress. Moreover, EBR also increased the net photosynthetic rate (Pn), light saturation point (LSP), maximal quantum yield of PSII photochemistry (Fv/Fm), actual photochemical efficiency of PSII (ФPSII), and photochemical quenching coefficient (qP), but decreased the intercellular CO2 concentration (Ci), light compensation point (LCP) and apparent quantum efficiency (AQE) under low temperature and weak light conditions. In addition, application of EBR to tomato leaves significantly enhanced the activities of nitrate reductase (NR), glutamate dehydrogenase (GDH), glutamine synthetase (GS), and glutamate synthase (GOGAT), but decreased the ammonium content and nitrite reductase (NiR) activity. We observed that EBR remarkably increased the contents of aspartic acid, threonine, serine, glycine, and phenylalanine, while decreasing the accumulation of cysteine, methionine, arginine, and proline under a combined low temperature and light stress. These results suggest that EBR could alleviate the combined stress-induced harmful effects on photosynthesis and nitrogen metabolism, thus leading to improved plant growth.

Genotype-dependent effect of exogenous 24-epibrassinolide on chromium-induced changes in ultrastructure and physicochemical traits in tobacco seedlings

Greenhouse hydroponic experiments were carried out using three different heavy metal accumulation tobacco genotypes to evaluate how different genotypes responded to chromium (Cr) toxicity in the presence of 24-epibrassinolide (EBR; a biologically active brassinosteroid). The results showed that Cr stress caused a marked reduction in plant biomass, chlorophyll content, chlorophyll fluorescence, and photosynthesis parameters but induced malondialdehyde accumulation and ultrastructure damage, with 2010-38 (L) less affected. Foliar application of 24-epibrassinolide (0.1 μM) on Cr-stressed plants greatly alleviated Cr-induced inhibition of growth and photosynthesis, oxidative stress and ultrastructure damage, decreased Cr accumulation in different parts of leaves and roots, with the exception of the upper and lower of leaves of genotype L, and maintained ion homeostasis. Regarding genotypes, L was more tolerant than M and H, as it absorbed less Cr and also performed better in all of the studied parameters. These findings suggest a potential role for 24-epibrassinolide in Cr stress alleviation and the utilization of elite genetic resources in future breeding programs to develop low Cr accumulation genotypes. These results advocate a positive role for 24-epibrassinolide in reducing pollutant residues from health point of view.

Interaction of epibrassinolide and selenium ameliorates the excess copper in Brassica juncea through altered proline metabolism and antioxidants

24-Epibrassinolide (EBL) and Selenium (Se) individually confer tolerance to various abiotic stresses, but their interactive effect in the regulation of copper (Cu) homeostasis in plants exposed to toxic levels of Cu is poorly investigated. This study provides an insight into the effects of EBL (foliar) and/or Se (through sand) on Brassica juncea plants exposed to toxic levels of Cu. The combined effect of EBL and Se on compartmentalization of Cu, oxidative stress markers, photosynthetic machinery and biochemical traits in B. juncea were analyzed. Application of EBL and Se through different mode modulated the compartmentalization of Cu in different parts of plants, enhanced the photosynthetic traits, and activities of various antioxidant enzymes and proline accumulation in B. juncea under excess copper levels. These enhanced levels of antioxidant enzymes, proline (osmolyte) accumulation triggered by combination of EBL and Se could have conferred tolerance to the B. juncea plants under toxic level of copper and also maintained Cu homeostasis in various parts of plants. This study indicates that combination of EBL and Se through different mode is an operative approach for Cu detoxification in plants and could be exploited for removal of excess copper from polluted soil.

Root proteomics reveals cucumber 24-epibrassinolide responses under Ca(NO3)2 stress

The application of exogenous 24-epibrassinolide promotes Brassinosteroids intracellular signalling in cucumber, which leads to differentially expressed proteins that participate in different life process to relieve Ca(NO 3 ) 2 damage. NO3 (-) and Ca(2+) are the main anion and cation of soil secondary salinization during greenhouse cultivation. Brassinosteroids (BRs), steroidal phytohormones, regulate various important physiological and developmental processes and are used against abiotic stress. A two-dimensional electrophoresis gel coupled with MALDI-TOF/TOF MS was performed to investigate the effects of exogenous 24-epibrassinolide (EBL) on proteomic changes in cucumber seedling roots under Ca(NO3)2 stress. A total of 80 differentially accumulated protein spots in response to stress and/or exogenous EBL were identified and grouped into different categories of biological processes according to Gene Ontology. Under Ca(NO3)2 stress, proteins related to nitrogen metabolism and lignin biosynthesis were induced, while those related to cytoskeleton organization and cell-wall neutral sugar metabolism were inhibited. However, the accumulation of abundant proteins involved in protein modification and degradation, defence mechanisms against antioxidation and detoxification and lignin biosynthesis by exogenous EBL might play important roles in salt tolerance. Real-time quantitative PCR was performed to investigate BR signalling. BR signalling was induced intracellularly under Ca(NO3)2 stress. Exogenous EBL can alleviate the root indices, effectively reduce the Ca(2+) content and increase the K(+) content in cucumber roots under Ca(NO3)2 stress. This study revealed the differentially expressed proteins and BR signalling-associated mRNAs induced by EBL in cucumber seedling roots under Ca(NO3)2 stress, providing a better understanding of EBL-induced salt resistance in cucumber seedlings. The mechanism for alleviation provides valuable insight into improving Ca(NO3)2 stress tolerance of other horticultural plants.

BRI1-Associated Receptor Kinase 1 Regulates Guard Cell ABA Signaling Mediated by Open Stomata 1 in Arabidopsis

Stomatal movements are critical in regulating gas exchange for photosynthesis and water balance between plant tissues and the atmosphere. The plant hormone abscisic acid (ABA) plays key roles in regulating stomatal closure under various abiotic stresses. In this study, we revealed a novel role of BAK1 in guard cell ABA signaling. We found that the brassinosteroid (BR) signaling mutant bak1 lost more water than wild-type plants and showed ABA insensitivity in stomatal closure. ABA-induced OST1 expression and reactive oxygen species (ROS) production were also impaired in bak1. Unlike direct treatment with H2O2, overexpression of OST1 did not completely rescue the insensitivity of bak1 to ABA. We demonstrated that BAK1 forms a complex with OST1 near the plasma membrane and that the BAK1/OST1 complex is increased in response to ABA in planta. Brassinolide, the most active BR, exerted a negative effect on ABA-induced formation of the BAK1/OST1 complex and OST1 expression. Moreover, we found that BAK1 and ABI1 oppositely regulate OST1 phosphorylation in vitro, and that ABI1 interacts with BAK1 and inhibits the interaction of BAK1 and OST1. Taken together, our results suggest that BAK1 regulates ABA-induced stomatal closure in guard cells.

[Combined effects of 24-epibrassinolide and salinity on the growth and physiological perfor-mance of Ulva prolifera]

In order to study the combined effects of brassinosteroids and salinity on the growth and physiological performance of Ulva prolifera under low temperature condition, we investigated the growth, chlorophyll content, chlorophyll fluorescence parameters, soluble protein and carbohydrate contents in this algae, which was grown under three salinity in the presence or absence of 24-epibrassinolide. The results showed that, compared to control salinity (25) treatment, the growth rate of U. prolifera was enhanced by 45.9% under the moderate hyposaline condition (10), but decreased under low salinity (5) treatment, which showed high contents of chlorophyll and soluble protein. However, the presence of EBR (0.2 mg·L^-1) significantly reduced the growth of U. prolifera, especially under the control salinity (25) treatment, under which the fresh mass decreased and more spores were released. Additionally, the effective quantum yield (F_v'/F_m'), the activity of SOD and the content of soluble carbohydrate also decreased, but the soluble protein content increased under the control salinity treatment in the presence of EBR. In conclusion, moderatehypo-saline condition could be used to enhance the growth of U. prolifera at 15 ℃, and under normal salinity (25), the EBR could be used to promote the release of spores and produce more materials for mass production of U. prolifera.

[Effect of exogenous brassinolide on morphological characters and contents of seven chemical constituents of Glycyrrhiza uralensis]

The transplants of the two-year-old Glycyrrhiza uralensis were subjected to four concentration of brassinolide (BR 0.1, 0.4, 0.7, 1.0 mg•L⁻¹) in July. The morphological characters ( plant height, stem diameter, nodes number, internode length and root length , root thick, root fresh weight and root dry weight ) were measured and seven kinds of chemical constituents (glycyrrhizic acid, liquiritin, isoliquiritin, liquiritigenin, isoliquiritigenin, liquiritin apioside, isoliquiritin apioside) were determined by HPLC with the aim of increasing sinter output and improving quality of G. uralensis. Then the long-term dynamic changes of these morphological characters and chemical compositions' content were analyzed. The results showed that morphological characters of plant height, stem diameter, root length , root thick, root fresh weight and root dry weight increased remarkably with the 0.7 mg•L⁻¹ BR stimulating 2 months later,the increase rates were： 15.09%,6.15%,16.52%,8.46%,21.90%,29.41%, respectively. The content of glycyrrhizic acid, liquiritin, isoliquiritin, liquiritigenin, liquiritin apioside, isoliquiritin apioside were increased 20.16%,45.31%,53.56%,27.66%,23.54%,8.46% with the 0.7 mg•L⁻¹ BR stimulating 2 months later. The best effects were achieved in 2 months after brassinolide stimulating. The conclusions prove that morphological characters and the main chemical constituents accumulation of G. uralensis could be effected by exogenous BR stimulation in certain case.

The alternative respiratory pathway is involved in brassinosteroid-induced environmental stress tolerance in Nicotiana benthamiana

Brassinosteroids (BRs), plant steroid hormones, play essential roles in modulating cell elongation, vascular differentiation, senescence, and stress responses. However, the mechanisms by which BRs regulate plant mitochondria and resistance to abiotic stress remain largely unclear. Mitochondrial alternative oxidase (AOX) is involved in the plant response to a variety of environmental stresses. In this report, the role of AOX in BR-induced tolerance against cold, polyethylene glycol (PEG), and high-light stresses was investigated. Exogenous applied brassinolide (BL, the most active BR) induced, while brassinazole (BRZ, a BR biosynthesis inhibitor) reduced alternative respiration and AOX1 expression in Nicotiana benthamiana. Chemical scavenging of H2O2 and virus-induced gene silencing (VIGS) of NbRBOHB compromised the BR-induced alternative respiratory pathway, and this result was further confirmed by NbAOX1 promoter analysis. Furthermore, inhibition of AOX activity by chemical treatment or a VIGS-based approach decreased plant resistance to environmental stresses and compromised BR-induced stress tolerance. Taken together, our results indicate that BR-induced AOX capability might contribute to the avoidance of superfluous reactive oxygen species accumulation and the protection of photosystems under stress conditions in N. benthamiana.

Role of AINTEGUMENTA-like gene NtANTL in the regulation of tobacco organ growth

The Nicotiana tabacum AINTEGUMENTA-like gene (NtANTL), encoding one of AP2/ERF transcription factors, is a putative ortholog of the AtANT gene from Arabidopsis thaliana. In wild-type tobacco plants, the NtANTL gene was expressed in the actively dividing young flowers, shoot apices, and calluses, while the level of its mRNA increased considerably after treatment with exogenous 6-benzylaminopurine, indoleacetic acid and 24-epibrassinolide. We found a positive correlation among the expression levels of NtANTL, cyclin NtCYCD3;1 and cyclin-dependent kinase NtCDKB1-1 genes, suggesting possible molecular links between AINTEGUMENTA and cell cycle regulators in tobacco plants. However, no correlation was observed between NtANTL, NtCYCD3;1 and NtCDKB1-1 expression levels in response to NaCl and ABA. These observations indicate that the transcription factor NtANTL was not involved in the regulation of the cellular response to salinity nor did it affect the expression of NtCYCD3;1 and NtCDKB1-1 when tobacco plants were exposed to salt stress and ABA. In addition, we generated transgenic tobacco plants with both up-regulated and down-regulated expression of the NtANTL gene. Constitutive expression of the NtANTL gene contributed to an increase in the size of leaves and corolla of transgenic plants. Transgenic plants with reduced expression of the NtANTL gene had smaller leaves, flowers and stems, but showed a compensatory increase in the cell size of leaves and flowers. The results show the significance of the NtANTL gene for the control of organ growth by both cell division and expansion in tobacco plants.

SILAC-Based Mass Spectrometry Analysis Reveals That Epibrassinolide Induces Apoptosis via Activating Endoplasmic Reticulum Stress in Prostate Cancer Cells

Epibrassinolide (EBR) is a polyhydroxylated sterol derivative and biologically active compound of the brassinosteroids. In addition to well-described roles in plant growth, EBR induces apoptosis in the LNCaP prostate cancer cells expressing functional androgen receptor (AR). Therefore, it is suggested that EBR might have an inhibitory potential on androgen receptor signaling pathway. However, the mechanism by which EBR exerts its effects on LNCaP is poorly understood. To address this gap in knowledge, we used an unbiased global proteomics approach, i.e., stable-isotope labeling by amino acids in cell culture (SILAC). In total, 964 unique proteins were identified, 160 of which were differentially expressed after 12 h of EBR treatment. The quantification of the differentially expressed proteins revealed that the expression of the unfolded protein response (UPR) chaperone protein, calreticulin (CALR), was dramatically downregulated. The decrease in CALR expression was also validated by immunoblotting. Because our data revealed the involvement of the UPR in response to EBR exposure, we evaluated the expression of the other UPR proteins. We demonstrated that EBR treatment downregulated calnexin and upregulated BiP and IRE1α expression levels and induced CHOP translocation from the cytoplasm to nucleus. The translocation of CHOP was associated with caspase-9 and caspase-3 activation after a 12 h EBR treatment. Co-treatment of EBR with rapamycin, an upstream mTOR pathway inhibitor, prevented EBR-induced cell viability loss and PARP cleavage in LNCaP prostate cancer cells, suggesting that EBR could induce ER stress in these cells. In addition, we observed similar results in DU145 cells with nonfunctional androgen receptor. When proteasomal degradation of proteins was blocked by MG132 co-treatment, EBR treatment further induced PARP cleavage relative to drug treatment alone. EBR also induced Ca²⁺ sequestration, which confirmed the alteration of the ER pathway due to drug treatment. Therefore, we suggest that EBR promotes ER stress and induces apoptosis.

Lycopersicon esculentum under low temperature stress: an approach toward enhanced antioxidants and yield

Brassinosteroids (BRs) have been implicated to overcome various abiotic stresses, and low temperature stress poses a serious threat to productivity of various horticultural crops like tomato. Therefore, a study was conducted to unravel the possible role of BRs in conferring alleviation to low temperature stress in Lycopersicon esculentum. Twenty-day-old seedlings of tomato var. S-22 (chilling tolerant) and PKM-1 (chilling sensitive) were sown in earthen pots, and at 40 days stage of growth, plants were exposed to varied levels of low temperatures (10/3, 12/7, 20/14, or 25/18 °C) for 24 h in a growth chamber. At 50 days stage of growth, the foliage of plants were sprayed with 0 or 10(-8) M of BRs (28-homobrassinolide or 24-epibrassinolide), and 60-day-old plants were harvested to assess various physiological and biochemical parameters. Low temperatures induced a significant reduction in growth traits, chlorophyll content, and rate of photosynthesis in both the varieties differentially. Activities of antioxidant enzymes (catalase, peroxidase, and superoxide dismutase) and leaf proline content also increased substantially in both the varieties with decreasing temperature. On the other hand, treatment of BRs under stress and stress-free conditions significantly increased the aforesaid growth traits and biochemical parameters. Moreover, BRs further accelerated the antioxidative enzymes and proline content, which were already enhanced by the low temperature stress. Out of the two analogues of BRs tested, 24-epibrassinolide (EBL) was found more effective for both the varieties of tomato. EBL was found more potent stress alleviator against low temperature in both varieties of tomato.

[Effects of brassinolide on the antioxidant system and photosynthesis of cucumber seedlings under suboptimal temperature, light and salt environment]

The effects of 24-epibrassinolide (EBR) on antioxidant system and photosynthesis of cucumber seedlings were studied under suboptimal temperature, light and salt environment. Compared with the control, the leaf H2O2 content, lipid peroxidation and cell membrane permeability significantly increased, and the leaf net photosynthetic rate (Pn), stomatal conductance (g(s)), intercellular CO2 concentration (Ci), transpiration rate (Tr) and dry matter accumulation decreased by 39.3%, 40.0%, 21.2%, 47.2% and 35.9% in the suboptimal environment, respectively. Applying EBR could further improve the antioxidant enzyme activity, reduce the H2O2 content and membrane permeability of seedlings, alleviate the drop range of Pn, g(s) and Tr, improve the growth of seedlings and increase the dry matter accumulation by 25.9%. Therefore, EBR treatment could keep higher photosynthetic performance to effectively promote cucumber seedlings growth through adjusting the protective enzyme activity and reducing membrane lipid peroxide level under suboptimal temperature, light and salt environment.

RNA Interference Knockdown of BRASSINOSTEROID INSENSITIVE1 in Maize Reveals Novel Functions for Brassinosteroid Signaling in Controlling Plant Architecture

Brassinosteroids (BRs) are plant hormones involved in various growth and developmental processes. The BR signaling system is well established in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) but poorly understood in maize (Zea mays). BRASSINOSTEROID INSENSITIVE1 (BRI1) is a BR receptor, and database searches and additional genomic sequencing identified five maize homologs including duplicate copies of BRI1 itself. RNA interference (RNAi) using the extracellular coding region of a maize zmbri1 complementary DNA knocked down the expression of all five homologs. Decreased response to exogenously applied brassinolide and altered BR marker gene expression demonstrate that zmbri1-RNAi transgenic lines have compromised BR signaling. zmbri1-RNAi plants showed dwarf stature due to shortened internodes, with upper internodes most strongly affected. Leaves of zmbri1-RNAi plants are dark green, upright, and twisted, with decreased auricle formation. Kinematic analysis showed that decreased cell division and cell elongation both contributed to the shortened leaves. A BRASSINOSTEROID INSENSITIVE1-ETHYL METHANESULFONATE-SUPPRESSOR1-yellow fluorescent protein (BES1-YFP) transgenic line was developed that showed BR-inducible BES1-YFP accumulation in the nucleus, which was decreased in zmbri1-RNAi. Expression of the BES1-YFP reporter was strong in the auricle region of developing leaves, suggesting that localized BR signaling is involved in promoting auricle development, consistent with the zmbri1-RNAi phenotype. The blade-sheath boundary disruption, shorter ligule, and disrupted auricle morphology of RNAi lines resemble KNOTTED1-LIKE HOMEOBOX (KNOX) mutants, consistent with a mechanistic connection between KNOX genes and BR signaling.

24-epibrassinolide mitigates the adverse effects of manganese induced toxicity through improved antioxidant system and photosynthetic attributes in Brassica juncea

The objective of this study was to establish relationship between manganese-induced toxicity and antioxidant system response in Brassica juncea plants and also to investigate whether brassinosteroids activate antioxidant system to confer tolerance to the plants affected with manganese induced oxidative stress. Brassica juncea plants were administered with 3, 6, or 9 mM manganese at 10-day stage for 3 days. At 31-day stage, the seedlings were sprayed with deionized water (control) or 10(-8) M of 24-epibrassinolide, and plants were harvested at 45-day stage to assess growth, leaf gas-exchange traits, and biochemical parameters. The manganese treatments diminished growth along with photosynthetic attributes and carbonic anhydrase activity in the concentration-dependent manner, whereas it enhanced lipid peroxidation, electrolyte leakage, accumulation of H2O2 as well as proline, and various antioxidant enzymes in the leaves of Brassica juncea which were more pronounced at higher concentrations of manganese. However, the follow-up application of 24-epibrassinolide to the manganese stressed plants improved growth, water relations, and photosynthesis and further enhanced the various antioxidant enzymes viz. catalase, peroxidase, and superoxide dismutase and content of proline. The elevated level of antioxidant enzymes as well as proline could have conferred tolerance to the manganese-stressed plants resulting in improved growth and photosynthetic attributes.

[Effects of exogenous EBR and NO signal on antioxidant system and low response gene expression under cold stress on maize embryo]

In this study, Xianyu 335, a maize hybrid, was used to investigate the effects of 24-Epibrassinolide (EBR, a synthetic BR) on antioxidant capacity and low-temperature response gene expression in maize embryo germination under low temperature (LT) stress. The germination rate of maize seeds under LT stress was not affected by EBR, but the seed activity index and seedling growth were improved. EBR increased the activities of some antioxidative enzymes including SOD, POD, CAT and GR, and the contents of non-enzymatic antioxidants, such as GSH and proline, and induced the accumulation of nitric oxide (NO). NO scavenging c-PTIO and NOS inhibitor L- NAME decreased but NO donor SNP increased the enzyme activities of CAT and POD, and the content of proline, indicating NO mediated the EBR-induced antioxidant capacity. The gene expression pattern analysis showed that the expression of P5CS1, CBF1, CBF3 and COR15a was induced by LT stress, and further increased by EBR treatment in maize embryo, while their expression was suppressed by c-PTIO and L-NAME, and improved by SNP, which implied LT-responsed genes were regulated by NO. These results demonstrated that NO was involved in the EBR-induced LT tolerance in maize embryo by modulating the antioxidative capacity and the expression of LT-responsive genes.

The effect of exogenous 24-epibrassinolide on the ecdysteroid content in the leaves of Spinacia oleracea L

The aim of this study was to show whether/how the application of exogenous 24-epibrassinolide can affect the content of ecdysteroids in spinach leaves. Brassinosteroids and ecdysteroids, structurally related phytosterols, show effect on a range of processes in plants. Brassinosteroids increase biomass yield in some species, photosynthesis and resistance to stress, and ecdysteroids show effect on proteins responsible for binding of CO2 or water cleavage. The mutual interaction of these sterols in plants is unclear. The UPLC-(+)ESI-MS/MS analyses of extracts of treated and untreated spinach (Spinacia oleracea L.) leaves show that the application of exogenous 24-epibrassinolide does influence the ecdysteroid content in plant tissues. The response differs for the major ecdysteroids and also differs from that for the minor ones and is dependent on the developmental stage of the leaves within the same plant or the 24-epibrassinolide concentration applied.

Ethylene mediates brassinosteroid-induced stomatal closure via Gα protein-activated hydrogen peroxide and nitric oxide production in Arabidopsis

Brassinosteroids (BRs) are essential for plant growth and development; however, whether and how they promote stomatal closure is not fully clear. In this study, we report that 24-epibrassinolide (EBR), a bioactive BR, induces stomatal closure in Arabidopsis (Arabidopsis thaliana) by triggering a signal transduction pathway including ethylene synthesis, the activation of Gα protein, and hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) production. EBR initiated a marked rise in ethylene, H(2)O(2) and NO levels, necessary for stomatal closure in the wild type. These effects were abolished in mutant bri1-301, and EBR failed to close the stomata of gpa1 mutants. Next, we found that both ethylene and Gα mediate the inductive effects of EBR on H(2)O(2) and NO production. EBR-triggered H(2)O(2) and NO accumulation were canceled in the etr1 and gpa1 mutants, but were strengthened in the eto1-1 mutant and the cGα line (constitutively overexpressing the G protein α-subunit AtGPA1). Exogenously applied H(2)O(2) or sodium nitroprusside (SNP) rescued the defects of etr1-3 and gpa1 or etr1 and gpa1 mutants in EBR-induced stomatal closure, whereas the stomata of eto1-1/AtrbohF and cGα/AtrbohF or eto1-1/nia1-2 and cGα/nia1-2 constructs had an analogous response to H(2)O(2) or SNP as those of AtrbohF or Nia1-2 mutants. Moreover, we provided evidence that Gα plays an important role in the responses of guard cells to ethylene. Gα activator CTX largely restored the lesion of the etr1-3 mutant, but ethylene precursor ACC failed to rescue the defects of gpa1 mutants in EBR-induced stomatal closure. Lastly, we demonstrated that Gα-activated H(2)O(2) production is required for NO synthesis. EBR failed to induce NO synthesis in mutant AtrbohF, but it led to H(2)O(2) production in mutant Nia1-2. Exogenously applied SNP rescued the defect of AtrbohF in EBR-induced stomatal closure, but H(2)O(2) did not reverse the lesion of EBR-induced stomatal closure in Nia1-2. Together, our results strongly suggest a signaling pathway in which EBR induces ethylene synthesis, thereby activating Gα, and then promotes AtrbohF-dependent H(2)O(2) production and subsequent Nia1-catalyzed NO accumulation, and finally closes stomata.

[The role of reactive oxygen species and calcium ions in the implementation of the stress-protective effect of brassinosteroids on plant cells]

The effect of the brassinosteroids (BS) 24-epibrassiniolide and 24-epicastasterone on the thermoresistance of wheat coleoptile (Triticum aestivum L.) and their generation of the superoxide anion radical and antioxidant enzymes activity were investigated. The treatment of coleoptiles with 10 nM solutions of BS caused a transient increase in O2·- generation and a subsequent increase in the activity of superoxide dismutase and catalase and an improvement in heat resistance. Pretreatment of coleoptiles with the NADPH oxidase inhibitor imidazole leveled the increase in production of the superoxide anion radical and prevented an increase in the activity of antioxidant enzymes and the development of cell thermostability. The investigated effects of BS were also depressed by the pretreatment of coleoptile segments with extracellular calcium chelator EGTA and inhibitor of ADP-ribosyl cyclase nicotinamide. A conclusion was made about the participation of calcium ions and reactive oxygen species generated by the action of NADPH oxidase in the implementation of the stress-protective effect of the BS in the cells of wheat coleoptile.

Cotton (Gossypium hirsutum) 14-3-3 proteins participate in regulation of fibre initiation and elongation by modulating brassinosteroid signalling

Cotton (Gossypium hirsutum) fibre is an important natural raw material for textile industry in the world. Understanding the molecular mechanism of fibre development is important for the development of future cotton varieties with superior fibre quality. In this study, overexpression of Gh14-3-3L in cotton promoted fibre elongation, leading to an increase in mature fibre length. In contrast, suppression of expression of Gh14-3-3L, Gh14-3-3e and Gh14-3-3h in cotton slowed down fibre initiation and elongation. As a result, the mature fibres of the Gh14-3-3 RNAi transgenic plants were significantly shorter than those of wild type. This 'short fibre' phenotype of the 14-3-3 RNAi cotton could be partially rescued by application of 2,4-epibrassinolide (BL). Expression levels of the BR-related and fibre-related genes were altered in the Gh14-3-3 transgenic fibres. Furthermore, we identified Gh14-3-3 interacting proteins (including GhBZR1) in cotton. Site mutation assay revealed that Ser163 in GhBZR1 and Lys51/56/53 in Gh14-3-3L/e/h were required for Gh14-3-3-GhBZR1 interaction. Nuclear localization of GhBZR1 protein was induced by BR, and phosphorylation of GhBZR1 by GhBIN2 kinase was helpful for its binding to Gh14-3-3 proteins. Additionally, 14-3-3-regulated GhBZR1 protein may directly bind to GhXTH1 and GhEXP promoters to regulate gene expression for responding rapid fibre elongation. These results suggested that Gh14-3-3 proteins may be involved in regulating fibre initiation and elongation through their interacting with GhBZR1 to modulate BR signalling. Thus, our study provides the candidate intrinsic genes for improving fibre yield and quality by genetic manipulation.

[Role of Ca ions in the induction of heat-resistance of wheat coleoptiles by brassinosteroids]

The involvement of Ca2+ into the signal transduction of exogenous brassinosteroids (BS) (24-epi-brassinolide-24-EBL and 24-epicastasterone-24-ECS) causing the increase of heat resistance of the cells of wheat (Triticum aestivum L.) coleoptiles was investigated using calcium chelator EGTA and inhibitor of phosphatidylinositol-specific phospholipase C--neomycin. Twenty-four-hour treatment of coleoptile segments with 10 nM solutions of 24-EBL and 24-ECS led to a transient increase in the generation of superoxide anion radical by cell surface and the subsequent activation of superoxide dismutase and catalase. Pretreatment of coleoptiles with EGTA and neomycin depressed to a considerable extent these effects and leveled the increase in heat resistance of wheat coleoptiles that were caused by BS. Possible mechanisms of involvement of calcium signaling into the formation of reactive oxygen species in plant cells and induction of heat resistance of plant cells by the action of exogenous BS have been discussed.

Epibrassinolide-induced apoptosis regardless of p53 expression via activating polyamine catabolic machinery, a common target for androgen sensitive and insensitive prostate cancer cells

BACKGROUND

Epibrassinolide (EBR), is a member of the brassinosteroids (BR), has been shown as an apoptotic inducer in different cancer cell lines. We previously showed that EBR induced apoptosis by activating polyamine catabolic pathway, which lead to the accumulation of cytotoxic compounds such as hydrogen peroxide and aldehydes in LNCaP and DU 145 prostate cancer cells. However, we found that LNCaP prostate cancer cells expressing functional androgen receptor (AR) was found more sensitive to EBR than those with non-functional AR (DU 145 cells).

RESULTS

To better understand the apoptotic effect of EBR, we aimed to investigate the cellular responses in p53 null, PC3 prostate cancer cells. We showed that EBR induced mitochondria-mediated and caspase-dependent apoptosis in wt and p53 stable transfected PC3 cells, which suggesting that EBR-induced apoptosis regardless of p53 expression. In addition, inhibition of p53 by pifithrin-α orthe activation of Mdm2 by Nutlin-3 co-treatment did not alter EBR induced PARP cleavage. Furthermore, EBR treatment was also induced apoptosis in both LNCaP(wt p53) and DU 145 (mt p53)cells, respectively. These all findings verified that EBR-induced apoptosis regardless of p53 expression. The PA catabolic pathway was also altered in PC3 cells causing the generation of reactive oxygen species (ROS) and intracellular PA pool decrease. However, the silencing of spermidine-spermineacetyltransferase (SSAT), a key enzyme at polyamine catabolic machinery prevented the EBR-induced apoptosis.

CONCLUSIONS

Therefore, we concluded that EBR-induced apoptosis was mainly related with PA catabolic pathway and independent from p53 expression.

Isolation of developing secondary xylem specific cellulose synthase genes and their expression profiles during hormone signalling in Eucalyptus tereticornis

Cellulose synthases (CesA) represent a group of β-1, 4 glycosyl transferases involved in cellulose biosynthesis. Recent reports in higher plants have revealed that two groups of CesA gene families exist, which are associated with either primary or secondary cell wall deposition. The present study aimed at identifying developing secondary xylem specific cellulose synthase genes from Eucalyptus tereticornis, a species predominantly used in paper and pulp industries in the tropics. The differential expression analysis of the three EtCesA genes using qRT-PCR revealed 49 to 87 fold relative expression in developing secondary xylem tissues. Three full length gene sequences of EtCesA1, EtCesA2 and EtCesA3 were isolated with the size of 2940, 3114 and 3123 bp, respectively. Phytohormone regulation of all three EtCesA genes were studied by exogenous application of gibberellic acid, naphthalene acetic acid, indole acetic acid and 2, 4-epibrassinolide in internode tissues derived from three-month-old rooted cuttings. All three EtCesA transcripts were upregulated by indole acetic acid and gibberellic acid. This study demonstrates that the increased cellulose deposition in the secondary wood induced by hormones can be attributed to the upregulation of xylem specific CesAs.

Role of H2O2 dynamics in brassinosteroid-induced stomatal closure and opening in Solanum lycopersicum

Brassinosteroids (BRs) are essential for plant growth and development; however, their roles in the regulation of stomatal opening or closure remain obscure. Here, the mechanism underlying BR-induced stomatal movements is studied. The effects of 24-epibrassinolide (EBR) on the stomatal apertures of tomato (Solanum lycopersicum) were measured by light microscopy using epidermal strips of wild type (WT), the abscisic acid (ABA)-deficient notabilis (not) mutant, and plants silenced for SlBRI1, SlRBOH1 and SlGSH1. EBR induced stomatal opening within an appropriate range of concentrations, whereas high concentrations of EBR induced stomatal closure. EBR-induced stomatal movements were closely related to dynamic changes in H(2)O(2) and redox status in guard cells. The stomata of SlRBOH1-silenced plants showed a significant loss of sensitivity to EBR. However, ABA deficiency abolished EBR-induced stomatal closure but did not affect EBR-induced stomatal opening. Silencing of SlGSH1, the critical gene involved in glutathione biosynthesis, disrupted glutathione redox homeostasis and abolished EBR-induced stomatal opening. The results suggest that transient H(2)O(2) production is essential for poising the cellular redox status of glutathione, which plays an important role in BR-induced stomatal opening. However, a prolonged increase in H(2)O(2) facilitated ABA signalling and stomatal closure.

PAG1, a cotton brassinosteroid catabolism gene, modulates fiber elongation

Cotton (Gossypium hirsutum) is the major source of natural textile fibers. Brassinosteroids (BRs) play crucial roles in regulating fiber development. The molecular mechanisms of BRs in regulating fiber elongation, however, are poorly understood. pagoda1 (pag1) was identified via an activation tagging genetic screen and characterized by genome walking and brassinolide (BL) supplementation. RNA-Seq analysis was employed to elucidate the mechanisms of PAG1 in regulating fiber development. pag1 exhibited dwarfism and reduced fiber length due to significant inhibition of cell elongation and expansion. BL treatment rescued its growth and fiber elongation. PAG1 encodes a homolog of Arabidopsis CYP734A1 that inactivates BRs via C-26 hydroxylation. RNA-Seq analyses showed that the constitutive expression of PAG1 downregulated the expression of genes involved in very-long-chain fatty acids (VLCFA) biosynthesis, ethylene-mediated signaling, response to cadmium, cell wall development, cytoskeleton organization and cell growth. Our results demonstrate that PAG1 plays crucial roles in regulating fiber development via controlling the level of endogenous bioactive BRs, which may affect ethylene signaling cascade by mediating VLCFA. Therefore, BR may be a critical regulator of fiber elongation, a role which may in turn be linked to effects on VLCFA biosynthesis, ethylene and cadmium signaling, cell wall- and cytoskeleton-related gene expression.

Effects of exogenous 24-epibrassinolide on the photosynthetic membranes under non-stress conditions

In the present work the effects of exogenous 24-epibrassinolide (EBR) on functional and structural characteristics of the thylakoid membranes under non-stress conditions were evaluated 48 h after spraying of pea plants with different concentrations of EBR (0.01, 0.1 and 1.0 mg.L(-1)). The results show that the application of 0.1 mg.L(-1) EBR has the most pronounced effect on the studied characteristics of the photosynthetic membranes. The observed changes in 540 nm light scattering and in the calorimetric transitions suggest alterations in the structural organization of the thylakoid membranes after EBR treatment, which in turn influence the kinetics of oxygen evolution, accelerate the electron transport rate, increase the effective quantum yield of photosystem II and the photochemical quenching. The EBR-induced changes in the photosynthetic membranes are most probably involved in the stress tolerance of plants.

An XA21-associated kinase (OsSERK2) regulates immunity mediated by the XA21 and XA3 immune receptors

The rice XA21 immune receptor kinase and the structurally related XA3 receptor confer immunity to Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial leaf blight. Here we report the isolation of OsSERK2 (rice somatic embryogenesis receptor kinase 2) and demonstrate that OsSERK2 positively regulates immunity mediated by XA21 and XA3 as well as the rice immune receptor FLS2 (OsFLS2). Rice plants silenced for OsSerk2 display altered morphology and reduced sensitivity to the hormone brassinolide. OsSERK2 interacts with the intracellular domains of each immune receptor in the yeast two-hybrid system in a kinase activity-dependent manner. OsSERK2 undergoes bidirectional transphosphorylation with XA21 in vitro and forms a constitutive complex with XA21 in vivo. These results demonstrate an essential role for OsSERK2 in the function of three rice immune receptors and suggest that direct interaction with the rice immune receptors is critical for their function. Taken together, our findings suggest that the mechanism of OsSERK2-meditated regulation of rice XA21, XA3, and FLS2 differs from that of AtSERK3/BAK1-mediated regulation of Arabidopsis FLS2 and EFR.

Exogenously applied 24-epi brassinolide reduces lignification and alters cell wall carbohydrate biosynthesis in the secondary xylem of Liriodendron tulipifera

The roles of brassinosteroids (BRs) in vasculature development have been implicated based on an analysis of Arabidopsis BR mutants and suspension cells of Zinnia elegans. However, the effects of BRs in vascular development of a woody species have not been demonstrated. In this study, 24-epi brassinolide (BL) was applied to the vascular cambium of a vertical stem of a 2-year-old Liriodendron, and the resulting chemical and anatomical phenotypes were characterized to uncover the roles of BRs in secondary xylem formation of a woody species. The growth in xylary cells was clearly promoted when treated with BL. Statistical analysis indicated that the length of both types of xylary cells (fiber and vessel elements) increased significantly after BL application. Histochemical analysis demonstrated that BL-induced growth promotion involved the acceleration of cell division and cell elongation. Histochemical and expression analysis of several lignin biosynthetic genes indicated that most genes in the phenylpropanoid pathway were significantly down-regulated in BL-treated stems compared to that in control stems. Chemical analysis of secondary xylem demonstrated that BL treatment induced significant modification in the cell wall carbohydrates, including biosynthesis of hemicellulose and cellulose. Lignocellulose crystallinity decreased significantly, and the hemicellulose composition changed with significant increases in galactan and arabinan. Thus, BL has regulatory roles in the biosynthesis and modification of secondary cell wall components and cell wall assembly during secondary xylem development in woody plants.

Effects of 24-epibrassinolide on plant growth, osmotic regulation and ion homeostasis of salt-stressed canola

This study evaluated effects of foliar spraying 24-epibrassinoide (24-EBL) on the growth of salt-stressed canola. Seedlings at the four-leaf stage were treated with 150 mM NaCl and different concentrations of 24-EBL (10(-6), 10(-8), 10(-10), 10(-12) M) for 15 days. A concentration of 10(-10) M 24-EBL was chosen as optimal and used in a subsequent experiment on plant biomass and leaf water potential parameters. The results showed that 24-EBL mainly promoted shoot growth of salt-stressed plants and also ameliorated leaf water status. Foliar spraying of salt-stressed canola with 24-EBL increased osmotic adjustment ability in all organs, especially in younger leaves and roots. This was mainly due to an increase of free amino acid content in upper leaves, soluble sugars in middle leaves, organic acids and proline in lower leaves, all of these compounds in roots, as well as essential inorganic ions. Na(+) and Cl(-) sharply increased in different organs under salt stress, and 24-EBL reduced their accumulation. 24-EBL improved the uptake of K(+), Ca(2+), Mg(2+) and NO3(-) in roots, which were mainly transported to upper leaves, while NO3(-) was mainly transported to middle leaves. Thus, 24-EBL improvements in ion homeostasis of K(+)/Na(+), Ca(2+)/Na(+), Mg(2+)/Na(+) and NO3(-)/Cl(-), especially in younger leaves and roots, could be explained. As most important parts, younger leaves and roots were the main organs protected by 24-EBL via improvement in osmotic adjustment ability and ion homeostasis. Further, physiological status of growth of salt-stressed canola was ameliorated after 24-EBL treatment.

Activation of polyamine catabolic enzymes involved in diverse responses against epibrassinolide-induced apoptosis in LNCaP and DU145 prostate cancer cell lines

Epibrassinolide (EBR) is a biologically active compound of the brassinosteroids, steroid-derived plant growth regulator family. Generally, brassinosteroids are known for their cell expansion and cell division-promoting roles. Recently, EBR was shown as a potential apoptotic inducer in various cancer cells without affecting the non-tumor cell growth. Androgen signaling controls cell proliferation through the interaction with the androgen receptor (AR) in the prostate gland. Initially, the development of prostate cancer is driven by androgens. However, in later stages, a progress to the androgen-independent stage is observed, resulting in metastatic prostate cancer. The androgen-responsive or -irresponsive cells are responsible for tumor heterogeneity, which is an obstacle to effective anti-cancer therapy. Polyamines are amine-derived organic compounds, known for their role in abnormal cell proliferation as well as during malignant transformation. Polyamine catabolism-targeting agents are being investigated against human cancers. Many chemotherapeutic agents including polyamine analogs have been demonstrated to induce polyamine catabolism that depletes polyamine levels and causes apoptosis in tumor models. In our study, we aimed to investigate the mechanism of apoptotic cell death induced by EBR, related with polyamine biosynthetic and catabolic pathways in LNCaP (AR+), DU145 (AR-) prostate cancer cell lines and PNT1a normal prostate epithelial cell line. Induction of apoptotic cell death was observed in prostate cancer cell lines after EBR treatment. In addition, EBR induced the decrease of intracellular polyamine levels, accompanied by a significant ornithine decarboxylase (ODC) down-regulation in each prostate cancer cell and also modulated ODC antizyme and antizyme inhibitor expression levels only in LNCaP cells. Catabolic enzymes SSAT and PAO expression levels were up-regulated in both cell lines; however, the specific SSAT and PAO siRNA treatments prevented the EBR-induced apoptosis only in LNCaP (AR+) cells. In a similar way, MDL 72,527, the specific PAO and SMO inhibitor, co-treatment with EBR during 24 h, reduced the formation of cleaved fragments of PARP in LNCaP (AR+) cells.