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.

Roles of jasmonates and brassinosteroids in rice responses to high temperature stress——A review

High temperature (HT) stress has become one of the most detrimental stresses in crop production among constantly changing environmental factors.Exploiting approaches to enhance crop thermotolerance would have great significance in assuaging adverse effects of HT stress on crop growth and development.As jasmonates (JAs) and brassinosteroids (BRs) are novel phytohormones and play important roles in responses to biotic and abiotic stresses and in a wide range of plant developmental processes,this paper reviewed the roles and mechanisms of JAs and BRs in mitigating HT stress,with focus on rice (Oryza sativa L.) subjected to HT stress during anthesis.It is demonstrated that JAs alleviate spikelet-opening impairment and BRs ameliorate pistil fertilization ability under HT stress during anthesis of rice,although there are controversial observations.Activating the defense system,enhancing osmotic regulation,protecting photosynthesis,and interacting with other phytohormones,especially with ethylene and abscisic acid,are main physiological mechanisms by which JAs or BRs attenuate HT stress to plants.Elevating levels of JAs or BRs in plants could be considered as an important approach to enhance crop thermotolerance through breeding new varieties.Using JAs or BRs as chemical regulators and adopting proper water and nitrogen management practices could reduce the harm of HT stress to rice.Further research is needed to elucidate the roles of JAs and BRs in different plant tissues in responses to HT stress under different genetic backgrounds and environments,reveal the molecular mechanism underlying JAs and BRs mediating HT stress,understand the cross-talk between phytohormones in modulating HT stress,and establish integrated crop management to minimize the hazard of HT stress in rice production.

Brassinosteroids modulate nitrogen physiological response and promote nitrogen uptake in maize(Zea mays L.)

Brassinosteroids(BRs)are steroid hormones that function in plant growth and development and response to environmental stresses and nutrient supplies.However,few studies have investigated the effect of BRs in modulating the physiological response to nitrogen(N)supply in maize.In the present study,BR signalingdeficient mutant zmbri1-RNAi lines and exogenous application of 2,4-epibrassinolide(e BL)were used to study the role of BRs in the regulation of physiological response in maize seedlings supplied with N.Exogenous application of e BL increased primary root length and plant biomass,but zmbri1 plants showed shorter primary roots and less plant biomass than wild-type plants under low N(LN)and normal N(NN)conditions.LN induced the expression of the BR signaling-associated genes Zm DWF4,Zm CPD,Zm DET2,and Zm BZR1 and the production of longer primary roots than NN.Knockdown of Zm BRI1 weakened the biological effects of LN-induced primary root elongation.e BL treatment increased N accumulation in shoots and roots of maize seedlings exposed to LN or NN treatment.Correspondingly,zmbri1 plants showed lower N accumulation in shoots and roots than wild-type plants.Along with reduced N accumulation,zmbri1 plants showed lower NO3-fluxes and^(15)NO_(3)^(-)uptake.The expression of nitrate transporter(NRT)genes(Zm NPF6.4,Zm NPF6.6,Zm NRT2.1,Zm NRT2.2)was lower in zmbri1 than in wild-type roots,but e BL treatments up-regulated the transcript expression of NRT genes.Thus,BRs modulated N physiological response and regulated the transcript expression of NRT genes to promote N uptake in maize.

Brassinosteroids and Plant Responses to Heavy Metal Stress. An Overview

Soil contamination with heavy metals has become a world-wide problem, leading to the loss in agricultural productivity. Plants have a remarkable ability to take up and accumulate heavy metals from their external environment and it is well known that high levels of heavy metals affect different physiological and metabolic processes. Brassinosteroids are considered as the sixth class of plant hormones and they are essential for plant growth and development. These compounds are able of inducing abiotic stress tolerance in plants. In this paper, information about brassinosteroids and plant responses to heavy metal stress is reviewed.

Brassinosteroids promote seed development and physiological maturity of oilseed rape (Brassica napus L.)

Long developmental stage and late harvest time of winter rapeseed (Brassica napus L.) have great negative effects on rice planting of rice-rapeseed farming system in China. Early maturity improvement of rapeseed is necessary. ‘Zhongshuang 11’, an elite winter rapeseed cultivar, was used in consecutive field experiments during 2010-2012. At initial flowering stage, plants were consecutively sprayed with 0.1 mg/L 2-4-Epibrassinolide(BR) for 3 d. Two hundred sampling pods from different plants were randomly collected to measure seed related indexes with a 4 d interval from 7 to 47 d after peak anthesis (DAPA).Seed color turned light brown at 31 or 35 DAPA after BR treatment, seed dry weight (DWT)was increased while seed moisture content (SMC) was decreased during seed development.DWT almost reached the maximum value when SMC was 33.20% at 31 DAPA in 2010-2011 and 35.29% at 35 DAPA in 2011-2012 growing season after BR treatment. Similarly,the maximum values of standard germination test (SGT), accelerated aging test (AAT)and cold test (CT) were observed at 31 or 35 DAPA after BR treatment respectively. The high yield and seed oil content appeared at 31 or 35 DAPA accompanied with rapid decrease in total non-structural carbohydrate (TNC) in stems and leaves. Our study indicated that BR application advanced maturity of winter rapeseed by 4 to 8 days.

Brassinosteroids fine-tune secondary and primary sulfur metabolism through BZR1-mediated transcriptional regulation

For adaptation to ever-changing environments,plants have evolved elaborate metabolic systems coupled to a regulatory network for optimal growth and defense. Regulation of plant secondary metabolic pathways such as glucosinolates(GSLs) by defense phytohormones in response to different stresses and nutrient deficiency has been intensively investigated, while how growth-promoting hormone balances plant secondary and primary metabolism has been largely unexplored. Here, we found that growth-promoting hormone brassinosteroid(BR) inhibits GSLs accumulation while enhancing biosynthesis of primary sulfur metabolites, including cysteine(Cys) and glutathione(GSH) both in Arabidopsis and Brassica crops, fine-tuning secondary and primary sulfur metabolism to promote plant growth. Furthermore, we demonstrate that of BRASSINAZOLE RESISTANT 1(BZR1), the central component of BR signaling, exerts distinct transcriptional inhibition regulation on indolic and aliphatic GSL via direct MYB51 dependent repression of indolic GSL biosynthesis, while exerting partial MYB29 dependent repression of aliphatic GSL biosynthesis. Additionally, BZR1 directly activates the transcription of APR1 and APR2 which encodes rate-limiting enzyme adenosine 5′-phosphosulfate reductases in the primary sulfur metabolic pathway.In summary, our findings indicate that BR inhibits the biosynthesis of GSLs to prioritize sulfur usage for primary metabolites under normal growth conditions.These findings expand our understanding of BR promoting plant growth from a metabolism perspective.

Wetting alternating with partial drying during grain filling increases lysine biosynthesis in inferior rice grain

Lysine content is a criterion of the nutritional quality of rice.Understanding the process of lysine biosynthesis in early-flowering superior grain(SG)and late-flowering inferior grain(IG)of rice would advance breeding and cultivation to improve nutritional quality.However,little information is available on differences in lysine anabolism between SG and IG and the underlying mechanism,and whether and how irrigation regimes affect lysine anabolism in these grains.A japonica rice cultivar was grown in the field and two irrigation regimes,continuous flooding(CF)and wetting alternating with partial drying(WAPD),were imposed from heading to the mature stage.Lysine content and activities of key enzymes of lysine biosynthesis,and levels of brassinosteroids(BRs)were lower in the IG than in the SG at the early grainfilling stage but higher at middle and late grain-filling stages.WAPD increased activities of these key enzymes,BR levels,and contents of lysine and total amino acids in IG,but not SG relative to CF.Application of 2,4-epibrassinolide to rice panicles in CF during early grain filling reproduced the effects of WAPD,but neither treatment altered the activities of enzymes responsible for lysine catabolism in either SG or IG.WAPD and elevated BR levels during grain filling increased lysine biosynthesis in IG.Improvement in lysine biosynthesis in rice should focus on IG.

Strigolactones and Brassinosteroids Antagonistically Regulate the Stability of the D53-OsBZR1 Complex to Determine FC1 Expression in Rice Tillering

Rice tillering,a key architecture trait determ ining grain yield,is highly regulated by a class of newly identified phytohorm ones,strigolactones(SLs).How ever,the whole SL signaling pathw ay from the receptor to dow nstream transcription factors to finally inhibit tillering remains unrevealed.In this study,we first found that brassinosteroids(BRs)strongly enhance tillering by prom oting bud outgrow th in rice,which is largely different from the function of BRs in Arabidopsis.Genetic and biochem ical analyses indicated that both the SL and BR signaling pathw ays control rice tillering by regulating the stability of D53 and/or the OsBZR1 RLA1-DLT module,a transcriptional complex in the rice BR signaling pathway.We further found that D53 interacts with OsBZR1 to inhibit the expression of FC1,a local inhibitor of tillering,and that this inhibition depends on direct DNA binding by OsBZR1,which recruits D53 to the FC1 promoter in rice buds.Taken together,these findings uncover a mechanism illustrating how SLs and BRs coordinately regulate rice tillering via the early responsive gene FC1.

Brassinosteroids Regulate Root Growth, Development, and Symbiosis

Brassinosteroids （BRs） are natural plant hormones critical for growth and development. BR-deficient or signaling mutants show significantly shortened root phenotypes. But for a long time, it was thought that these phenotypes were solely caused by reduced root cell elongation in the mutants. Functions of BRs in regulating root development have been largely neglected. Recent detailed analyses, however, revealed that BRs are not only involved in root cell elongation but are also involved in many aspects of root development, such as maintenance of meristem size, root hair formation, lateral root initiation, gravitropic response, mycorrhiza formation, and nodulation in legume species. In this review, current findings on the functions of BRs in mediating root growth, development, and symbiosis are discussed.

Brassinosteroids Regulate the Differential Growth of Arabidopsis Hypocotyls through Auxin Signaling Components IAA19 and ARF7

Brassinosteroids （BRs） are an important class of phytohormones which regulates a wide range of physiological processes. Genetic and physiological studies have revealed that BR responses usually depend on an intact auxin signaling pathway. Here, we demonstrate that high BR concentration or enhanced BR signaling induce the differential growth of etiolated hypocotyls and result in the morphological changes, while auxin-resistant mutants, msg2 （dominant mutant of IAA19） and arf7, are insensitive to the BR effect and can partially suppress the phenotype of bzrl-D （dominant mutant of BZR1 with enhanced BR signaling）. Interestingly, BZR1 protein can directly bind to the promoter regions of both IAA19 and ARFT, indicating that IAA19 and ARF7 mediate the BR-induced differential growth by serving as direct targets of BZR1. Systemic microarray analysis revealed that a number of BR-responsive genes showed reduced BR response in msg2, confirming that BR employs auxin signaling components IAA19 and ARF7 to modulate the specific downstream processes. These results provide informative clues on the crosstalk of BR-auxin signaling and the mechanisms of BR-auxin effects in regulating differential growth.

Organ-specific effects of brassinosteroids on stomatal production coordinate with the action of TOO MANY MOUTHS

In Arabidopsis,stomatal development initiates after protodermal cells acquire stomatal lineage cell fate.Stomata or their precursors communicate with their neighbor epidermal cells to ensure the ＂one cell spacing＂ rule.The signals from EPF/EPFL peptide ligands received by TOO MANY MOUTHS（TMM）and ERECTA-family receptors are supposed to be transduced by YODA MAPK cascade.A basic helix-loop-helix transcription factor SPEECHLESS（SPCH） is another key regulator of stomatal cell fate determination and asymmetric entry divisions,and SPCH activity is regulated by YODA MAPK cascade.Brassinosteroid（BR） signaling,one of the most well characterized signal transduction pathways in plants,contributes to the control of stomatal production.But opposite organ-specific effects of BR on stomatal production were reported.Here we confirm thatstomatal production in hypocotyls is controlled by BR levels.YODA and CYCD4 are not essential for BR stomata-promoting function.Furthermore,we found that BR could confer tmm hypocotyls clustered stomatal phenotype,indicating that the BR organ-specific effects on stomatal production might coordinate with the TMM organ-specific actions.

Brassinosteroids inhibit miRNA-mediated translational repression by decreasing AGO1 on the endoplasmic reticulum

Translational repression is a conserved mechanism in microRNA(miRNA)-guided gene silencing.In Arabidopsis,ARGONAUTE1(AGO1),the major miRNA effector,localizes in the cytoplasm for mRNA cleavage and at the endoplasmic reticulum(ER)for translational repression of target genes.However,the mechanism underlying miRNA-mediated translational repression is poorly understood.In particular,how the subcellular partitioning of AGO1 is regulated is largely unexplored.Here,we show that the plant hormone brassinosteroids(BRs)inhibit miRNA-mediated translational repression by negatively regulating the distribution of AGO1 at the ER in Arabidopsis thaliana.We show that the protein levels rather than the transcript levels of miRNA target genes were reduced in BR-deficient mutants but increased under BR treatments.The localization of AGO1 at the ER was significantly decreased under BR treatments while it was increased in the BR-deficient mutants.Moreover,ROTUNDIFOLIA3(ROT3),an enzyme involved in BR biosynthesis,co-localizes with AGO1 at the ER and interacts with AGO1 in a GW motif-dependent manner.Complementation analysis showed that the AGO1-ROT3 interaction is necessary for the function of ROT3.Our findings provide new clues to understand how miRNA-mediated gene silencing is regulated by plant endogenous hormones.

Biological Activity of Brassinosteroids and Relationship of Structure to Plant Growth Promoting Effects

Brassinolide (BR) is a new potent growth promoting steroid substance which was first isolated from rape pollen by Grove et al. in 1979. Since then a number of BR analogues, such as homobrassinolide 2 and epibrassinolide 3, have been discovered in plant. Unnatural compounds with similar structure to brassinolide have

Brassinosteroids promote thermotolerance through releasing BIN2-mediated phosphorylation and suppression of HsfA1 transcription factors in Arabidopsis

High temperature adversely affects plant growth and development.The steroid phytohormones brassinosteroids(BRs)are recognized to play important roles in plant heat stress responses and thermotolerance,but the underlying mechanisms remain obscure.Here,we demonstrate that the glycogen synthase kinase 3(GSK3)-like kinase BRASSINOSTEROID INSENSITIVE2(BIN2),a negative component in the BR signaling pathway,interacts with the master heat-responsive transcription factors CLASS A1 HEAT SHOCK TRANSCRIPTION FACTORS(HsfA1s).Furthermore,BIN2 phosphorylates HsfA1d on T263 and S56 to suppress its nuclear localization and inhibit its DNA-binding ability,respectively.BR signaling promotes plant thermotolerance by releasing the BIN2 suppression of HsfA1d to facilitate its nuclear localization and DNA binding.Our study provides insights into the molecular mechanisms by which BRs promote plant thermotolerance by strongly regulating HsfA1d through BIN2 and suggests potential ways to improve crop yield under extreme high temperatures.

The Mechanisms of Brassinosteroids＇ Action： From Signal Transduction to Plant Development

Brassinosteroids play diverse roles in plant growth and development. Plants deficient in brassinosteroid （BR） biosynthesis or defective in signal transduction show many abnormal developmental phenotypes, indicating the importance of both BR biosynthesis and the signaling pathway in regulating these biological processes. Recently, using genetics, proteomics, genomics, cell biology, and many other approaches, more components involved in the BR signaling pathway were identified. Furthermore, the physiological, cellular, and molecular mechanisms by which BRs regulate various aspects of plant development, are being discovered. These include root development, anther and pollen development and formation, stem elongation, vasculature differentiation, and cellulose biosynthesis, suggesting that the biological functions of BRs are far beyond promoting cell elongation, This review will focus on the up-to-date progresses about regulatory mechanisms of the BR signaling pathway and the physiological and molecular mechanisms whereby BRs regulate plant growth and development.

Homeostasis of Brassinosteroids Regulated by DRL1, a Putative Acyltransferase in Arabidopsis

Brassinosteroids （BRs） play essential roles in regulating various aspects of plant growth and development and in responding to diverse environmental cues, and their metabolism is an important way to regulate their homeosta-sis in plants. Here, we identified a dominant mutant, dwarf and round leaf-1 （drll-D）, which exhibits weak BR-deficient or BR-insensitive mutant phenotypes, including short and round leaves, prolonged senescence, dwarfed shape, and altered expression levels of the BR-responsive genes. Hypocotyl length and root inhibition assays suggest that the drll-D mutant responds to BRs normally, but has decreased BR signaling outputs. The endogenous levels of several BRs, includ-ing typhasterol （TY）, 6-deoxotyphasterol （6-deoxoTY）, and 6-deoxocastasterone （6-deoxoCS）, are significantly lower in the drll-D mutant than in the wild-type. The DRL1 gene encodes an acyltransferase and is widely expressed in leaves, roots, flowers, and siliques. Plants without DRL1 and its homologs are larger with an enhanced BR signaling. The expres-sion of DRL1 was induced by eBL and inhibited by ABA. DRL1 is involved in the BR metabolism likely by catalyzing the BR conjugation through esterification, which plays important roles in regulating the BR homeostasis and responding to abiotic stresses in Arabidopsis.

Brassinosteroids enhance salicylic acid-mediated immune responses by inhibiting BIN2 phosphorylation of clade I TGA transcription factors in Arabidopsis

Salicylic acid (SA) plays an important role in plant immune response, including resistance to pathogens and systemic acquired resistance. Two major components, NONEXPRESSOR OF PATHOGENESIS-RELATED GENES (NPRs) and TGACG motif-binding transcription factors (TGAs), are known to mediate SA signaling, which might also be orchestrated by other hormonal and environmental changes. Nevertheless, the molecular and functional interactions between SA signaling components and other cellular signaling pathways remain poorly understood. Here we showed that the steroid plant hormone brassinosteroid (BR) promotes SA responses by inactivating BR-INSENSITIVE 2 (BIN2), which inhibits the redox-sensitive clade I TGAs in Arabidopsis. We found that both BR and the BIN2 inhibitor bikinin synergistically increase SA-mediated physiological responses, such as resistance to Pst DC3000. Our genetic and biochemical analyses indicated that BIN2 functionally interacts with TGA1 and TGA4, but not with other TGAs. We further demonstrated that BIN2 phosphorylates Ser-202 of TGA4, resulting in the suppression of the redox-dependent interaction between TGA4 and NPR1 as well as destabilization of TGA4. Consistently, transgenic Arabidopsis overexpressing TGA4-YFP with a S202A mutation displayed enhanced SA responses compared to the wild-type TGA4-YFP plants. Taken together, these results suggest a novel crosstalk mechanism by which BR signaling coordinates the SA responses mediated by redox-sensitive clade I TGAs.

GhIQD10 interacts with GhCaM7 to control cotton fiber elongation via calcium signaling

IQ67-domain(IQD)proteins function in plant defense and in organ development.The mechanisms by which they influence cotton fiber development are unknown.In the present study,GhIQD10 was expressed mainly in the transition period of cotton fiber development,and GhIQD10-overexpression lines showed shorter fibers.GhIQD10 interacted with GhCaM7 and the interaction was inhibited by Ca^(2+).In in vitro ovule culture,Ca^(2+)rescued the shorter-fiber phenotype of GhIQD10-overexpression lines,which were insensitive to the Ca^(2+)channel inhibitor verapamil and the Ca^(2+)pool release channel blocker 2-aminoethoxydiphenyl borate.We conclude that GhIQD10 affects cotton fiber elongation via Ca^(2+)signaling by interacting with GhCaM7.Brassinosteroid(BR)biosynthesis and signaling genes were up-regulated in GhIQD10-overexpression lines.Fiber development in these lines was not affected by epibrassinolide or the BR biosynthesis inhibitor brassinozole,indicating that the influence of GhIQD10 on fiber elongation was not associated with BR.

不同时期喷施油菜素内酯对菊花花期和观赏品质的影响

在菊花（Chrysanthemum morifolium Ramat.）“姹紫嫣红”的苗期、光周期诱导期、绿蕾形成期、绿蕾期、苗期＋光周期诱导期＋绿蕾形成期＋绿蕾期,分别用50 μg/L油菜素内酯（Brassinosteroid,BR）的水溶液对菊花进行叶面喷施,初步研究了在菊花生长发育的不同时期BR对菊花花期和观赏品质的影响.结果表明,在苗期和苗期＋光周期诱导期＋绿蕾形成期＋绿蕾期喷施50 μg/L BR可以推迟菊花花期3～4 d;在光周期诱导期、绿蕾形成期、绿蕾期和苗期＋光周期诱导期＋绿蕾形成期＋绿蕾期喷施50 μg/L BR均能提高菊花盛花期叶片中叶绿素含量、花瓣中花青素含量和降低丙二醛（MDA）含量,有助于观赏品质的改善,且随处理时期后移效应增强,多时期处理存在累加效应.

Physiological mechanism underlying spikelet degeneration in rice

The phenomenon of degenerated spikelets is very common in cereals, and considered as a serious physiological defect and a main constraint to grain production. Understanding the physiological mechanism in which spikelet degeneration occurs would have great significance in enhancing yield potential in grain crops. Taking rice as an example, the paper reviewed the physiological mechanism underlying spikelet degeneration, with focus on the roles of phytohormones in regulating the process. There are several hypotheses for the spikelet degeneration, such as resource limitation, self-organization, and primigenic dominance. However, convincing evidences are not enough to support the assumptions. Phytohormones including auxins, cytokinins, gibberellins, abscisic acid, and ethylene are involved in regulating spikelet degeneration in cereals. The new phytohormones of brassinosteroids and polyamines have been observed to suppress spikelet degeneration in rice. The interactions among or between plant hormones may play a more important role in regulating spikelet degeneration. However, the information on such interactions is very limited. Some agronomic practices, especially proper water and nitrogen management, could reduce spikelet degeneration but the mechanism underlying remains unclear. Further research is needed to understand the cross-talk among/between phytohormones on spikelet degeneration, to reveal the physiological and molecular mechanism in which phytohormones and their interactions regulate the degeneration of spikelets, to exploit approaches to decrease spikelet degeneration and to elucidate their mechanism.