Brassinosteroid Signaling Pathway Research Articles

Functions and Mechanisms of Brassinosteroids in Regulating Crop Agronomic Traits.

Brassinosteroids (BRs) perform crucial functions controlling plant growth and developmental processes, encompassing many agronomic traits in crops. Studies of BR-related genes involved in agronomic traits have suggested that BRs could serve as a potential target for crop breeding. Given the pleiotropic effect of BRs, a systematic understanding of their functions and molecular mechanisms is conducive for application in crop improvement. Here, we summarize the functions and underlying mechanisms by which BRs regulate the several major crop agronomic traits, including plant architecture, grain size, as well as the specific trait of symbiotic nitrogen fixation in legume crops. For plant architecture, we discuss the roles of BRs in plant height, branching number, and leaf erectness and propose how progress in these fields may contribute to designing crops with optimal agronomic traits and improved grain yield by accurately modifying BR levels and signaling pathways.

BcBZR1 Regulates Leaf Inclination Angle in Non-Heading Chinese Cabbage (Brassica campestris ssp. chinensis Makino)

Brassinosteroids (BRs) play critical roles in plant growth by promoting cell elongation and division, leading to increased leaf inclination angles. BRASSINAZOLE RESISTANT 1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1) act as transcription factors in the brassinosteroid signaling pathway and are involved in several physiological activities regulated by BRs. In this study, we identified and cloned BcBZR1 from the heitacai non-heading Chinese cabbage (NHCC) cultivar. The sequence analysis showed that the coding sequence length of BcBZR1 is 996 bp, encoding 331 amino acid residues. Subcellular localization assays showed that BcBZR1 is localized in the nucleus and cytoplasm and that BcBZR1 protein is transported to the nucleus after receiving BR signals. Compared with Col-0, the leaf inclination angle was smaller in BcBZR1-OX. The EBR treatment experiment indicated that BRs regulate the differential expression of paclobutrazol resistance1 (PRE1) and ILI1 binding bHLH1 (IBH1) in the adaxial and abaxial cells of the petiole through BZR1, thus regulating the leaf inclination angle. The bimolecular fluorescence complementation (BiFC) assay indicated that BcBZR1 interacts with C-repeat Binding Factor2 (BcCBF2) and CBF3. Taken together, our findings not only validate the function of BcBZR1 in leaf inclination angle distribution in non-heading Chinese cabbage, but also contribute to the mechanism of leaf inclination angle regulation in this species under cold stress.

Comparative transcriptome and metabolome analysis revealed diversity in the response of resistant and susceptible rose (Rosa hybrida) varieties to Marssonina rosae.

Rose black spot disease caused by Marssonina rosae is among the most destructive diseases that affects the outdoor cultivation and production of roses; however, the molecular mechanisms underlying the defensive response of roses to M. rosae have not been clarified. To investigate the diversity of response to M. rosae in resistant and susceptible rose varieties, we performed transcriptome and metabolome analyses of resistant (KT) and susceptible (FG) rose varieties and identified differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in response to M. rosae at different time points. In response to M. rosae, DEGs and DAMs were mainly upregulated compared to the control and transcription factors were concentrated in the WRKY and AP2/ERF families. Gene Ontology analysis showed that the DEGs of FG were mainly enriched in biological processes, such as the abscisic acid-activated signaling pathway, cell wall, and defense response, whereas the DEGs of KT were mainly enriched in Golgi-mediated vesicle transport processes. Kyoto Encyclopedia of Genes and Genomes analysis showed that the DEGs of both varieties were concentrated in plant-pathogen interactions, plant hormone signal transduction, and mitogen-activated protein kinase signaling pathways, with the greatest number of DEGs associated with brassinosteroid (BR) in the plant hormone signal transduction pathway. The reliability of the transcriptome results was verified by qRT-PCR. DAMs of KT were significantly enriched in the butanoate metabolism pathway, whereas DAMs of FG were significantly enriched in BR biosynthesis, glucosinolate biosynthesis, and tryptophan metabolism. Moreover, the DAMs in these pathways were significantly positively correlated with the DEGs. Disease symptoms were aggravated when FG leaves were inoculated with M. rosae after 24-epibrassinolide treatment, indicating that the response of FG to M. rosae involves the BR signaling pathway. Our results provide new insights into the molecular mechanisms underlying rose response to M. rosae and lay a theoretical foundation for formulating rose black spot prevention and control strategies and cultivating resistant varieties.

Recent advances in understanding the regulatory mechanism of plasma membrane H+-ATPase through the brassinosteroid signaling pathway.

The polyhydroxylated steroid phytohormone brassinosteroids (BRs) control many aspects of plant growth, development and responses to environmental changes. Plasma membrane (PM) H+-ATPase, the well-known PM proton pump, is a central regulator in plant physiology, which mediates not only plant growth and development, but also adaptation to stresses. Recent studies highlight that PM H+-ATPase is at least partly regulated via the BR signaling. Firstly, the BR cell surface receptor BRASSINOSTEROID-INSENSITIVE 1 (BRI1) and multiple key components of BR signaling directly or indirectly influence PM H+-ATPase activity. Secondly, the SMALL AUXIN UP RNA (SAUR) gene family physically interacts with BRI1 to enhance organ development of Arabidopsis by activating PM H+-ATPase. Thirdly, RNA-sequencing (RNA-seq) assays showed that the expression of some SAUR genes is upregulated under the light or sucrose conditions, which is related to the phosphorylation state of the penultimate residue of PM H+-ATPase in a time-course manner. In this review, we describe the structural and functional features of PM H+-ATPase, and summarize recent progress toward understanding the regulatory mechanism of PM H+-ATPase by BRs, and briefly introduce how PM H+-ATPase activity is modulated by its own biterminal regions and the post-translational modifications.

The occurrence, inheritance, and segregation of complex genomic structural variation in synthetic Brassica napus

“Synthetic” allopolyploids recreated by interspecific hybridization play an important role in providing novel genomic variation for crop improvement. Such synthetic allopolyploids often undergo rapid genomic structural variation (SV). However, how such SV arises, is inherited and fixed, and how it affects important traits, has rarely been comprehensively and quantitively studied in advanced generation synthetic lines. A better understanding of these processes will aid breeders in knowing how to best utilize synthetic allopolyploids in breeding programs. Here, we analyzed three genetic mapping populations (735 DH lines) derived from crosses between advanced synthetic and conventional Brassica napus (rapeseed) lines, using whole-genome sequencing to determine genome composition. We observed high tolerance of large structural variants, particularly toward the telomeres, and preferential selection for balanced homoeologous exchanges (duplication/deletion events between the A and C genomes resulting in retention of gene/chromosome dosage between homoeologous chromosome pairs), including stable events involving whole chromosomes (“pseudoeuploidy”). Given the experimental design (all three populations shared a common parent), we were able to observe that parental SV was regularly inherited, showed genetic hitchhiking effects on segregation, and was one of the major factors inducing adjacent novel and larger SV. Surprisingly, novel SV occurred at low frequencies with no significant impacts on observed fertility and yield-related traits in the advanced generation synthetic lines. However, incorporating genome-wide SV in linkage mapping explained significantly more genetic variance for traits. Our results provide a framework for detecting and understanding the occurrence and inheritance of genomic SV in breeding programs, and support the use of synthetic parents as an important source of novel trait variation.

SlSERK3B Promotes Tomato Seedling Growth and Development by Regulating Photosynthetic Capacity.

Brassinosteroids (BRs) are a group of polyhydroxylated steroids for plant growth and development, regulating numerous physiological and biochemical processes and participating in multi-pathway signaling in plants. 24-Epibrassinolide (EBR) is the most commonly used BR for the investigation of the effects of exogenous steroidal phytohormones on plant physiology. Although SlSERK3B is considered a gene involved in the brassinosteroid (BR) signaling pathway, its specific role in plant growth and development has not been reported in detail. In this study, tomato (Solanum lycopersicum L.) seedlings treated with 0.05 μmol L-1 EBR showed a significant increase in plant height, stem diameter, and fresh weight, demonstrating that BR promotes the growth of tomato seedlings. EBR treatment increased the expression of the BR receptor gene SlBRI1, the co-receptor gene SlSERK3A and its homologs SlSERK3B, and SlBZR1. The SlSERK3B gene was silenced by TRV-mediated virus-induced gene silencing (VIGS) technology. The results showed that both brassinolide (BL) content and BR synthesis genes were significantly up-regulated in TRV-SlSERK3B-infected seedlings compared to the control seedlings. In contrast, plant height, stem diameter, fresh weight, leaf area and total root length were significantly reduced in silenced plants. These results suggest that silencing SlSERK3B may affect BR synthesis and signaling, thereby affecting the growth of tomato seedlings. Furthermore, the photosynthetic capacity of TRV-SlSERK3B-infected tomato seedlings was reduced, accompanied by decreased photosynthetic pigment content chlorophyll fluorescence, and photosynthesis parameters. The expression levels of chlorophyll-degrading genes were significantly up-regulated, and carotenoid-synthesising genes were significantly down-regulated in TRV-SlSERK3B-infected seedlings. In conclusion, silencing of SlSERK3B inhibited BR signaling and reduced photosynthesis in tomato seedlings, and this correlation suggests that SlSERK3B may be related to BR signaling and photosynthesis enhancement.

Characteristic analysis of BZR genes family and their responses to hormone treatments and abiotic stresses in Carya illinoinensis

As the core of Brassinosteroids (BR) signaling pathway, BR-resistant (BZR) transcription factor regulates thousands of targeted genes mediating photomophogenesis, pollen sterility, cell expansion and stress response. Pecan (Carya illinoinensis) is a famous trees species of Carya, and its nut has high nutritional and economic values. However, there has no report on BZR genes family in pecan yet. Herein, totals of seven CiBZR members were identified in pecan genome, which were predicted to be hydrophilic unstable proteins and located in the nucleus. CiBZR genes had close evolutionary relationships with CcBZRs and JrBZRs in both Carya cathayensis and Juglans regia. These seven CiBZR genes were located independently on 7 chromosomes without doubling or tandem duplication. Based on the analysis of conserved motifs and gene structures, CiBZR genes were divided into three categories. More than 40 cis-acting elements were found in the 2 kb promoter regions of CiBZRs, which were mainly involved in hormone, light, and stress response, and plant growth and development. Notably, some of these CiBZR proteins were mainly located in the nucleus, had the self-activation ability and interaction relationship with BIN2 kinase, and negatively regulated the expression of CiCPD and CiDWF4. Gene expressions analysis further showed that CiBZR genes could express in many tissues and shared similar expression trends during embryo development. Moreover, most CiBZR genes responded to BR, Gibberellin (GA), Strigolactone (SL), salt, acid and osmotic stress. This study provides theoretical basis for the subsequent study on the role of CiBZR family genes in plant growth, development and stress responses.

HvGSK1.1 Controls Salt Tolerance and Yield through the Brassinosteroid Signaling Pathway in Barley.

Brassinosteroids (BRs) are a class of plant steroid hormones that are essential for plant growth and development. BRs control important agronomic traits and responses to abiotic stresses. Through the signaling pathway, BRs control the expression of thousands of genes, resulting in a variety of biological responses. The key effectors of the BR pathway are two transcription factors (TFs): BRASSINAZOLE RESISTANT 1 (BZR1) and BRI1-EMSSUPPRESSOR 1 (BES1). Both TFs are phosphorylated and inactivated by the Glycogen synthase kinase 3 BRASSINOSTEROID INSENSITIVE2 (BIN2), which acts as a negative regulator of the BR pathway. In our study, we describe the functional characteristics of HvGSK1.1, which is one of the GSK3/SHAGGY-like orthologs in barley. We generated mutant lines of HvGSK1.1 using CRISPR/Cas9 genome editing technology. Next Generation Sequencing (NGS) of the edited region of the HvGSK1.1 showed a wide variety of mutations. Most of the changes (frameshift, premature stop codon, and translation termination) resulted in the knock-out of the target gene. The molecular and phenotypic characteristics of the mutant lines showed that the knock-out mutation of HvGSK1.1 improved plant growth performance under salt stress conditions and increased the thousand kernel weight of the plants grown under normal conditions. The inactivation of HvGSK1.1 enhanced BR-dependent signaling, as indicated by the results of the leaf inclination assay in the edited lines. The plant traits under investigation are consistent with those known to be regulated by BRs. These results, together with studies of other GSK3 gene members in other plant species, suggest that targeted editing of these genes may be useful in creating plants with improved agricultural traits.

Effects of Enhanced Resistance and Transcriptome Analysis of Twig Blight Disease by Exogenous Brassinolide in Myrica rubra.

Twig blight disease is the primary disease that affects the production of Myrica rubra in China. It was reported that exogenous brassinolide (BL) can improve disease resistance in plants. Here, we examined the effects of exogenous BL on disease resistance, chlorophyll contents, antioxidant enzyme activity, ROS accumulation, and key gene expression of M. rubra to analyze the mechanism of BR-induced resistance of twig blight disease in M. rubra. The results demonstrated that 2.0 mg·L-1 of BL could significantly lessen the severity of twig blight disease in M. rubra. Exogenous BL increased the contents of chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll. Moreover, exogenous BL also significantly enhanced the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and decreased malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation in leaves, such as H2O2 and O2·-. Additionally, exogenous BL dramatically up-regulated the expression of pathogenesis-related (PR) genes such as MrPR1, MrPR2, and MrPR10, as well as important genes such as MrBAK1, MrBRI1, and MrBZR1 involved in brassinosteroid (BR) signaling pathway. The transcriptome analysis revealed that a total of 730 common differentially expressed genes (DEGs) under BL treatment were found, and these DEGs were primarily enriched in four Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Based on these findings, nine important candidate genes related to the resistance of twig blight disease under BL treatment were further identified. In this study, we elucidated the effects of exogenous BL on enhancing the resistance of M. rubra to twig blight disease and preliminary analyzed the potential mechanism of resistance induction, which will provide a crucial foundation for the management and prevention of twig blight disease in M. rubra.

Brassinosteroid Signaling Pathways: Insights into Plant Responses under Abiotic Stress.

With the growing global population, abiotic factors have emerged as a formidable threat to agricultural food production. If left unaddressed, these stress factors might reduce food yields by up to 25% by 2050. Plants utilize natural mechanisms, such as reactive oxygen species scavenging, to mitigate the adverse impacts of abiotic stressors. Diverse plants exhibit unique adaptations to abiotic stresses, which are regulated by phytohormones at various levels. Brassinosteroids (BRs) play a crucial role in controlling essential physiological processes in plants, including seed germination, xylem differentiation, and reproduction. The BR cascade serves as the mechanism through which plants respond to environmental stimuli, including drought and extreme temperatures. Despite two decades of research, the complex signaling of BRs under different stress conditions is still being elucidated. Manipulating BR signaling, biosynthesis, or perception holds promise for enhancing crop resilience. This review explores the role of BRs in signaling cascades and summarizes their substantial contribution to plants' ability to withstand abiotic stresses.

Transcription factors BZR2/MYC2 modulate brassinosteroid and jasmonic acid crosstalk during pear dormancy.

Bud dormancy is an important physiological process during winter. Its release requires a certain period of chilling. In pear (Pyrus pyrifolia), the abscisic acid (ABA)-induced expression of DORMANCY-ASSOCIATED MADS-box (DAM) genes represses bud break, whereas exogenous gibberellin (GA) promotes dormancy release. However, with the exception of ABA and GA, the regulatory effects of phytohormones on dormancy remain largely uncharacterized. In this study, we confirmed brassinosteroids (BRs) and jasmonic acid (JA) contribute to pear bud dormancy release. If chilling accumulation is insufficient, both 24-epibrassinolide (EBR) and methyl jasmonic acid (MeJA) can promote pear bud break, implying that they positively regulate dormancy release. BRASSINAZOLE RESISTANT 2 (BZR2), which is a BR-responsive transcription factor, inhibited PpyDAM3 expression and accelerated pear bud break. The transient overexpression of PpyBZR2 increased endogenous GA, JA, and JA-Ile levels. In addition, the direct interaction between PpyBZR2 and MYELOCYTOMATOSIS 2 (PpyMYC2) enhanced the PpyMYC2-mediated activation of Gibberellin 20-oxidase genes PpyGA20OX1L1 and PpyGA20OX2L2 transcription, thereby increasing GA3 contents and accelerating pear bud dormancy release. Interestingly, treatment with 5 μm MeJA increased the bud break rate, while also enhancing PpyMYC2-activated PpyGA20OX expression and increasing GA3,4 contents. The 100 μm MeJA treatment decreased the PpyMYC2-mediated activation of the PpyGA20OX1L1 and PpyGA20OX2L2 promoters and suppressed the inhibitory effect of PpyBZR2 on PpyDAM3 transcription, ultimately inhibiting pear bud break. In summary, our data provide insights into the crosstalk between the BR and JA signaling pathways that regulate the BZR2/MYC2-mediated pathway in the pear dormancy release process.

Integration of miRNA dynamics and drought tolerant QTLs in rice reveals the role of miR2919 in drought stress response

To combat drought stress in rice, a major threat to global food security, three major quantitative trait loci for ‘yield under drought stress’ (qDTYs) were successfully exploited in the last decade. However, their molecular basis still remains unknown. To understand the role of secondary regulation by miRNA in drought stress response and their relation, if any, with the three qDTYs, the miRNA dynamics under drought stress was studied at booting stage in two drought tolerant (Sahbaghi Dhan and Vandana) and one drought sensitive (IR 20) cultivars. In total, 53 known and 40 novel differentially expressed (DE) miRNAs were identified. The primary drought responsive miRNAs were Osa-MIR2919, Osa-MIR3979, Osa-MIR159f, Osa-MIR156k, Osa-MIR528, Osa-MIR530, Osa-MIR2091, Osa-MIR531a, Osa-MIR531b as well as three novel ones. Sixty-one target genes that corresponded to 11 known and 4 novel DE miRNAs were found to be co-localized with the three qDTYs, out of the 1746 target genes identified. We could validate miRNA-mRNA expression under drought for nine known and three novel miRNAs in eight different rice genotypes showing varying degree of tolerance. From our study, Osa-MIR2919, Osa-MIR3979, Osa-MIR528, Osa-MIR2091-5p and Chr01_11911S14Astr and their target genes LOC_Os01g72000, LOC_Os01g66890, LOC_Os01g57990, LOC_Os01g56780, LOC_Os01g72834, LOC_Os01g61880 and LOC_Os01g72780 were identified as the most promising candidates for drought tolerance at booting stage. Of these, Osa-MIR2919 with 19 target genes in the qDTYs is being reported for the first time. It acts as a negative regulator of drought stress tolerance by modulating the cytokinin and brassinosteroid signalling pathway.

Genomic Colinearity and Transcriptional Regulatory Networks of BES1 Gene Family in Horticultural Plants Particularly Kiwifruit and Peach

The BES1 transcription factor family was unique and critical in plants. The BES1s played roles in the Brassinosteroid (BR) signaling pathway and participated in the plant’s development, maturation, and stress response process. This study investigated the function of the BES1 gene family of 48 horticultural crops by phylogenetic and genomic colinearity network analysis. In addition, the transcriptional regulatory networks had analyzed the process during biotic stress, abiotic stress, fruit development, and postharvest of kiwifruit and peach. The study illustrated a comprehensive understanding of the phylogenetic relationships of the BES1 family in plant genomes and the prediction of growth and development of kiwifruit and peach fruits and maturation-related BES1 members, laying the foundation for further functional studies of BES1 genes in the future.

OsbHLH92, in the noncanonical brassinosteroid signaling pathway, positively regulates leaf angle and grain weight in rice.

Modifications of plant architecture can increase planting density, regulate photosynthesis, and improve crop yields. Many basic helix-loop-helix (bHLH) transcription factors participate in the brassinosteroid (BR) signaling pathway and are critical for plant architecture morphogenesis in rice. However, the number of identified bHLH genes suitable for improving production value is still limited. In this study, we cloned Lam1, encoding the typical bHLH transcription factor OsbHLH92. OsbHLH92 knockout (KO) lines exhibit erect leaves. Decreases in the number and size of parenchyma cell layers on the adaxial side of the lamina joint in KO lines were the main reason for the decreased leaf angle. Genetic experiments verify that OsBU1 and its homologs are downstream of OsbHLH92, which is involved in the noncanonical RGA1-mediated BR signaling pathway. OsbHLH91, an OsbHLH92 homolog, plays both conserved and differentiated roles relative to OsbHLH92. Notably, OsbHLH92-KO lines show erect leaves without the acquisition of adverse agronomic traits. Moreover, by driving a specific panicle promoter, OsbHLH92 can greatly increase productivity by at least 10%. This study identifies new components of the BR signaling pathway, demonstrates the importance of OsbHLH92 in improving planting density and crop productivity, and broadens our knowledge of typical and atypical bHLH family members in rice.

Uncovering transcriptional reprogramming during callus development in soybean: insights and implications.

Callus, a valuable tool in plant genetic engineering, originates from dedifferentiated cells. While transcriptional reprogramming during callus formation has been extensively studied in Arabidopsis thaliana, our knowledge of this process in other species, such as Glycine max, remains limited. To bridge this gap, our study focused on conducting a time-series transcriptome analysis of soybean callus cultured for various durations (0, 1, 7, 14, 28, and 42 days) on a callus induction medium following wounding with the attempt of identifying genes that play key roles during callus formation. As the result, we detected a total of 27,639 alterations in gene expression during callus formation, which could be categorized into eight distinct clusters. Gene ontology analysis revealed that genes associated with hormones, cell wall modification, and cell cycle underwent transcriptional reprogramming throughout callus formation. Furthermore, by scrutinizing the expression patterns of genes related to hormones, cell cycle, cell wall, and transcription factors, we discovered that auxin, cytokinin, and brassinosteroid signaling pathways activate genes involved in both root and shoot meristem development during callus formation. In summary, our transcriptome analysis provides significant insights into the molecular mechanisms governing callus formation in soybean. The information obtained from this study contributes to a deeper understanding of this intricate process and paves the way for further investigation in the field.

Brassinosteroid transcription factor BES1 modulates nitrate deficiency by promoting NRT2.1 and NRT2.2 transcription in Arabidopsis.

Nitrogen (N) is one of the most essential mineral elements for plants. Brassinosteroids (BRs) play key roles in plant growth and development. Emerging evidence indicates that BRs participate in the responses to nitrate deficiency. However, the precise molecular mechanism underlying the BR signaling pathway in regulating nitrate deficiency remains largely unknown. The transcription factor BES1 regulates the expression of many genes in response to BRs. Root length, nitrate uptake and N concentration of bes1-D mutants were higher than those of wild-type under nitrate deficiency. BES1 levels strongly increased under low nitrate conditions, especially in the non-phosphorylated (active) form. Furthermore, BES1 directly bound to the promoters of NRT2.1 and NRT2.2 to promote their expression under nitrate deficiency. Taken together, BES1 is a key mediator that links BR signaling under nitrate deficiency by modulating high affinity nitrate transporters in plants.

The regulatory module MdBZR1-MdCOL6 mediates brassinosteroid- and light-regulated anthocyanin synthesis in apple.

The anthocyanin content is an important indicator of the nutritional value of most fruits, including apple (Malus domestica). Anthocyanin synthesis is coordinately regulated by light and various phytohormones. In this study on apple, we revealed the antagonistic relationship between light and brassinosteroid (BR) signaling pathways, which is mediated by BRASSINAZOLE-RESISTANT 1 (MdBZR1) and the B-box protein MdCOL6. The exogenous application of brassinolide inhibited the high-light-induced anthocyanin accumulation in red-fleshed apple seedlings, whereas increases in the light intensity decreased the endogenous BR content. The overexpression of MdBZR1 inhibited the anthocyanin synthesis in apple plants. An exposure to a high-light intensity induced the degradation of dephosphorylated MdBZR1, resulting in functional impairment. MdBZR1 was identified as an upstream repressor of MdCOL6, which promotes anthocyanin synthesis in apple plants. Furthermore, MdBZR1 interacts with MdCOL6 to attenuate its ability to activate MdUFGT and MdANS transcription. Thus, MdBZR1 negatively regulates MdCOL6-mediated anthocyanin accumulation. Our study findings have clarified the molecular basis of the integration of light and BR signals during the regulation of anthocyanin biosynthesis, which is an important process influencing fruit quality.

Transcriptional reprogramming during recovery from drought stress in Eucalyptus grandis.

The importance of drought as a constraint to agriculture and forestry is increasing with climate change. Genetic improvement of plants' resilience is one of the mitigation strategies to curb this threat. Although recovery from drought stress is important to long-term drought adaptation and has been considered as an indicator of dehydration tolerance in annual crops, this has not been well explored in forest trees. Thus, we aimed to investigate the physiological and transcriptional changes during drought stress and rewatering in Eucalyptus grandis W. Hill ex Maiden. We set up a greenhouse experiment where we imposed drought stress on 2-year-old seedlings and rewatered the recovery group after 17days of drought. Our measurement of leaf stomatal conductance (gs) showed that, while gs was reduced by drought stress, it fully recovered after 5days of rewatering. The RNA-seq analysis from stem samples revealed that genes related to known stress responses such as phytohormone and reactive oxygen species signaling were upregulated, while genes involved in metabolism and growth were downregulated due to drought stress. We observed reprogramming of signal transduction pathways and metabolic processes at 1day of rewatering, indicating a quick response to rewatering. Our results suggest that recovery from drought stress may entail alterations in the jasmonic acid, salicylic acid, ethylene and brassinosteroid signaling pathways. Using co-expression network analysis, we identified hub genes, including the putative orthologs of ABI1, ABF2, ABF3, HAI2, BAM1, GolS2 and SIP1 during drought and CAT2, G6PD1, ADG1 and FD-1 during recovery. Taken together, by highlighting the molecular processes and identifying key genes, this study gives an overview of the mechanisms underlying the response of E. grandis to drought stress and recovery that trees may face repeatedly throughout their long life cycle. This provides a useful reference to the identification and further investigation of signaling pathways and target genes for future tree improvement.

Green means go: Green light promotes hypocotyl elongation via brassinosteroid signaling.

Although many studies have elucidated the mechanisms by which different wavelengths of light (blue, red, far-red, or ultraviolet-B [UV-B]) regulate plant development, whether and how green light regulates plant development remains largely unknown. Previous studies reported that green light participates in regulating growth and development in land plants, but these studies have reported conflicting results, likely due to technical problems. For example, commercial green light-emitting diode light sources emit a little blue or red light. Here, using a pure green light source, we determined that unlike blue, red, far-red, or UV-B light, which inhibits hypocotyl elongation, green light promotes hypocotyl elongation in Arabidopsis thaliana and several other plants during the first 2-3 d after planting. Phytochromes, cryptochromes, and other known photoreceptors do not mediate green-light-promoted hypocotyl elongation, but the brassinosteroid (BR) signaling pathway is involved in this process. Green light promotes the DNA binding activity of BRI1-EMS-SUPPRESSOR 1 (BES1), a master transcription factor of the BR pathway, thus regulating gene transcription to promote hypocotyl elongation. Our results indicate that pure green light promotes elongation via BR signaling and acts as a shade signal to enable plants to adapt their development to a green-light-dominant environment under a canopy.

Water deficit aggravated the inhibition of photosynthetic performance of maize under mercury stress but is alleviated by brassinosteroids.

Mercury (Hg) significantly inhibits maize (Zea mays L.) production, which could be aggravated by water deficit (WD) due to climate change. However, there is no report on the maize in response to combined their stresses. This work was conducted for assessing the response and adaptive mechanism of maize to combined Hg and WD stress using two maize cultivars, Xianyu (XY) 335 and Yudan (YD) 132. The analysis was based on plant growth, physiological function, and transcriptomic data. Compared with the single Hg stress, Hg accumulation in whole plant and translocation factor (TF) under Hg+WD were increased by 64.51% (1.44mgkg-1) and 260.00%, respectively, for XY 335; and 50.32% (0.62mgkg-1) and 220.02%, respectively, for YD 132. Combined Hg and WD stress further increased the reactive oxygen species accumulation, aggravated the damage of the thylakoid membrane, and decreased chlorophyll content compared with single stress. For example, Chl a and Chl b contents of XY 335 were significantly decreased by 48.67% and 28.08%, respectively at 48h after Hg+WD treatment compared with Hg stress. Furthermore, transcriptome analysis revealed that most of down-regulated genes were enriched in photosynthetic-antenna proteins, photosynthesis, chlorophyll and porphyrin metabolism pathways (PsbS1, PSBQ1 and FDX1 etc.) under combined stress, reducing light energy capture and electron transport. However, most genes related to the brassinosteroids (BRs) signaling pathway were up-regulated under Hg+WD stress. Correspondingly, exogenous BRs significantly enhanced the maize tolerance to stress by decreasing Hg accumulation and TF, and raising activities of antioxidant enzyme, the content of chlorophyll and photosynthetic performance. The PI, Fv/Fm and Fv/Fo of Hg+WD+BR treatment were increased by 29.88%, 32.06%, and 14.56%, respectively, for XY 335 compared to Hg+WD. Overall, combined Hg and WD stress decreased photosynthetic efficiency by adversely affecting light absorption and electron transport, especially in stress-sensitive variety, but BRs could alleviate the inhibition of photosynthesis, providing a novel strategy for enhancing crop Hg and WD tolerance and food safety.