Brassinosteroids: Multidimensional Regulators of Plant Growth, Development, and Stress Responses

PhWRKY30 activates salicylic acid biosynthesis to positively regulate antiviral defense response in petunia

Petunia (Petunia hybrida) plants are highly threatened by a diversity of viruses, causing substantial damage to ornamental quality and seed yield. However, the regulatory mechanism of virus resistance in petunia is largely unknown. Here, we revealed that a member of petunia WRKY transcription factors, PhWRKY30, was dramatically up-regulated following Tobacco rattle virus (TRV) infection. Down-regulation of PhWRKY30 through TRV-based virus-induced gene silencing increased green fluorescent protein (GFP)-marked TRV RNA accumulation and exacerbated the symptomatic severity. In comparison with wild-type (WT) plants, PhWRKY30-RNAi transgenic petunia plants exhibited a compromised resistance to TRV infection, whereas an enhanced resistance was observed in PhWRKY30-overexpressing (OE) transgenic plants. PhWRKY30 affected salicylic acid (SA) production and expression of arogenate dehydratase 1 (PhADT1), phenylalanine ammonia-lyase 1 (PhPAL1), PhPAL2b, nonexpressor of pathogenesis-related proteins 1 (PhNPR1), and PhPR1 in SA biosynthesis and signaling pathway. SA treatment restored the reduced TRV resistance to WT levels in PhWRKY30-RNAi plants, and application of SA biosynthesis inhibitor 2-aminoindan-2-phosphonic acid inhibited promoted resistance in PhWRKY30-OE plants. The protein-DNA binding assays showed that PhWRKY30 specifically bound to the promoter of PhPAL2b. RNAi silencing and overexpression of PhPAL2b led to decreased and increased TRV resistance, respectively. The transcription of a number of reactive oxygen species- and RNA silencing-associated genes was changed in PhWRKY30 and PhPAL2b transgenic lines. PhWRKY30 and PhPAL2b were further characterized to be involved in the resistance to Tobacco mosaic virus (TMV) invasion. Our findings demonstrate that PhWRKY30 positively regulates antiviral defense against TRV and TMV infections by modulating SA content.

BR signalling haplotypes contribute to indica-japonica differentiation for grain yield and quality in rice

The functional difference of natural variations in conserved BR signalling genes and the genetic basis of rice indica-japonica differentiation are important yet unknown. Here, we discovered natural variations of the four key components (OsBRI1, OsBAK1, OsGSK3 and OsBZR1) in BR signalling pathway by GWAS using an indicator of indica-japonica differentiation in rice. Two major BR signalling haplotypes (BSHs), caused by co-selected variations of the four genetically unlinked genes, were identified to be highly differentiated between rice subspecies. The genetic contributions of BSHs to grain yield and quality were much higher than that of each component. Introducing alleles of japonica into indica employing substitution lines of OsBAK1, complementation lines of OsGSK3 and genetic populations of OsBRI1/OsBAK1/OsGSK3 confirmed their functional differences between two subspecies. The BSH differentiation led to weaker interaction between OsBRI1 and OsBAK1, stronger autophosphorylation and kinase activity of OsGSK3, less RNA/proteins and stronger phosphorylation of OsBZR1, and weaker BR sensitivity in indica than japonica rice, and regular expression trends of BR-response genes between subspecies, and then synergistically enhanced yield and superior quality of indica. Our results demonstrate that BSHs contribute to rice inter-subspecies diversity, and will provide proof-of-concept breeding strategy and useful targets in crops.

Trihelix Transcription Factor OsTGS1 Regulates Grain Size and Weight in Rice

Grain size is one of the major factors determining rice grain yield. Nevertheless, our knowledge of the molecular mechanisms underlying the control rice grain size remains limited. Trihelix proteins are plant-specific transcription factors that regulate plant growth and development. However, their roles in modulating grain size in cereal crops are largely unknown. Here, we report the rice trihelix family gene Oryza sativa trihelix transcription factor related to grain size 1 (OsTGS1) as a novel regulator of grain size and weight. Mutation of OsTGS1 leads to large and heavy grains, whereas overexpression of OsTGS1 results in small and light grains. OsTGS1 regulates grain size by influencing cell division and cell expansion in spikelet hulls. OsTGS1 is expressed in various tissues, and its expression level increases during panicle development. The OsTGS1 protein is localized to the nucleus and exhibits transcriptional repressor activity. The screening of interacting proteins via a yeast two-hybrid assay revealed that OsTGS1 interacted with GSK3/SHAGGY-LIKE KINASE2 (GSK2), an important regulator of various agronomic traits, including grain size, in rice. Moreover, ostgs1 mutants are hypersensitive to exogenous brassinosteroid treatment, indicating that OsTGS1 may be involved in brassinosteroid signaling. Our study reveals the role of OsTGS1 in controlling grain size and provides a new gene resource for improving grain weight in rice.

Exploring omics solutions to reduce micro/nanoplastic toxicity in plants: A comprehensive overview

The proliferation of plastic waste, particularly in the form of microplastics (MPs) and nanoplastics (NPs), has emerged as a significant environmental challenge with profound implications for agricultural ecosystems. These pervasive pollutants accumulate in soil, altering its physicochemical properties and disrupting microbial communities. MPs/NPs can infiltrate plant systems, leading to oxidative stress and cytotoxic effects, which in turn compromise essential physiological functions such as water uptake, nutrient absorption, and photosynthesis. This situation threatens crop yield and health, while also posing risks to human health and food security through potential accumulation in the food chain. Despite increasing awareness of this issue, substantial gaps still remain in our understanding of the physiological and molecular mechanisms that govern plant responses to MP/NP stress. This review employs integrative omics techniques including genomics, transcriptomics, proteomics, metabolomics, and epigenomics to elucidate these responses. High-throughput methodologies have revealed significant genetic and metabolic alterations that enable plants to mitigate the toxicity associated with MPs/NPs. The findings indicate a reconfiguration of metabolic pathways aimed at maintaining cellular homeostasis, activation of antioxidant mechanisms, and modulation of gene expression related to stress responses. Additionally, epigenetic modifications suggest that plants adapt to prolonged plastics exposure, highlighting unexplored avenues for targeted research. By integrating various omics approaches, a comprehensive understanding of molecular interactions and their effects on plant systems can be achieved. This review underscores potential targets for biotechnological and agronomic interventions aimed at enhancing plant resilience by identifying key stress-responsive genes, proteins, and metabolites. Ultimately, this work addresses critical knowledge gaps and highlights the importance of multi-omics strategies in developing sustainable solutions to mitigate the adverse effects of MP/NP pollution in agriculture, thereby ensuring the integrity of food systems and ecosystems.

OsBSK3 and OsBSK2 regulate grain size and leaf angle via MAPK signaling pathway in rice

Grain size and leaf angle are key agronomic traits that determine the final yield. OsBSKs (BRASSINOSTEROID-SIGNALING KINASES) and OsMAPKs (MITOGEN ACTIVATED PROTEIN KINASE) are known to play essential roles in plant growth, development, and stress responses. However, the potential crosstalk between these pathways and their specific roles in regulating grain size and leaf angle remain largely unexplored in rice. Here, we characterized that OsBSKs regulate grain size and leaf angle in rice, and among these, OsBSK2 and OsBSK3 may play more critical roles. The grain size and leaf angle in osbsk3 and osbsk2 mutants are significantly smaller, whereas the OsBSK3-overexpressing lines (OsBSK3-OEs) exhibit considerably larger grain size and leaf angle compared to the others. Furthermore, both OsBSK3 and OsBSK2 interact with OsMKKK10, indirectly activating OsMAPK6 in plant cells. Notably, mutations in MAPK cascade components, such as smg2-1 (an osmkkk10 mutant), smg1-1 (an osmkk4 mutant), and dsg1 (an osmapk6 mutant), resulted in significantly reduced leaf angles. Moreover, these mutations were able to rescue the increased grain size and leaf angle observed in OsBSK3 overexpression lines. Additionally, we also identified OsWRKY53 as a potential downstream target of the OsBSKs-OsMKKK10-OsMKK4-OsMAPK6 cascade in the regulation of grain size and leaf angle. Taken together, the above results not only highlight the essential and specific roles of OsBSK3 and OsBSK2 in regulating rice grain size and leaf angle, but also reveal the mechanism which OsBSK3/OsBSK2 mediate MAPK cascade to regulate rice grain size and leaf angle.

Plant steroids on the move: mechanisms of brassinosteroid export

Brassinosteroids (BRs) are essential plant steroidal hormones that regulate growth and development. The recent discoveries of ATP-binding cassette subfamily B (ABCB) members, ABCB19 and ABCB1, as BR transporters highlight the significance of active export to the apoplast in maintaining BR homeostasis and enabling effective signaling. This review focuses on the latest progress in understanding ABCB-mediated BR transport, with particular attention to the structural and functional characterization of arabidopsis ABCB19 and ABCB1. These findings reveal both conserved and distinct features in substrate recognition and transport mechanisms, providing valuable insights into their roles in hormonal regulation. Additionally, the evolutionary conservation of ABC transporters in mediating steroid-based signaling across biological kingdoms underscores their fundamental biological significance.

Polarity-guided uneven mitotic divisions control brassinosteroid activity in proliferating plant root cells

Brassinosteroid hormones are positive regulators of plant organ growth, yet their function in proliferating tissues remains unclear. Here, through integrating single-cell RNA sequencing with long-term live-cell imaging of the Arabidopsis root, we reveal that brassinosteroid activity fluctuates throughout the cell cycle, decreasing during mitotic divisions and increasing during the G1 phase. The post-mitotic recovery of brassinosteroid activity is driven by the intrinsic polarity of the mother cell, resulting in one daughter cell with enhanced brassinosteroid signaling, while the other supports brassinosteroid biosynthesis. The coexistence of these distinct daughter cell states during the G1 phase circumvents a negative feedback loop to facilitate brassinosteroid production while signaling increases. Our findings uncover polarity-guided, uneven mitotic divisions in the meristem, which control brassinosteroid hormone activity to ensure optimal root growth.

Identification and overexpression of RNA-decapping protein GhLSM1BS: Enhancing cotton somatic embryogenesis through up-regulating brassinosteroid biosynthesis

We identified two splicing variants of GhLSM1B (GhLSM1BS and GhLSM1BL) with distinct expression patterns and predicted 3D structures, despite sharing the same nuclear localization. Overexpression of GhLSM1BS, but not GhLSM1BL, accelerated cotton callus proliferation and altered cell morphology during somatic embryogenesis, accompanied by altered expression of CYP450 family genes and elevated brassinosteroid levels.

Comparative single-cell transcriptomic map reveals divergence in leaves between two cotton species at cell type resolution

INTRODUCTION

Leaves are important functional organs in plants that determine yield and quality of crops. Upland cotton and sea-island cotton contribute more than 90% of the cotton fiber production annually. Deciphering and utilizing the diversity of leaf cells and functional genes underlying their divergences will be highly meaningful for cotton breeding.

OBJECTIVES

To investigate the conserved and divergent cell types of leaves between upland cotton and sea-island cotton, identify functional genes, and explore functional cell types in response to biotic and abiotic stresses in both species.

METHODS

Nuclei were isolated from leaves of upland cotton CRI12 and sea-island cotton XH21, respectively, and single-nucleus RNA-seq (snRNA-seq) was performed. Based on the orthologous genes, comparative single-cell transcriptomic map (CSCTM) of two cotton species was constructed to investigate conservation and divergence of cell types, and funtional genes were validated by virus induced gene silencing. Combining CSCTM, comparative genomic and transcriptomic analysis, functional cell types were identified in response to biotic and abiotic stresses.

RESULTS

A total of 22 and 20 distinct clusters were identified representing 6 main cell types in CRI12 and XH21, respectively. CSCTM analysis revealed a sea-island cotton-specific cell cluster, in which specifically expressed GbNF-YA7's role in pathogen resistance was validated. Meanwhile, the divergence of pigment gland development was revealed among cotton species and WRKY15 was identified to influence gossypol content without affecting pigment gland number. Moreover, integrated CSCTM and comparative genomic and transcriptomic analysis revealed genome variations could influence the gene expression in an elaborate cell type-specifc manner, highlighted the function of cotton leaf vascular tissue cells in Verticillium wilt resistance and putative functional differentiation of conserved abiotic stresses response genes. Additionally, different cell types might assume distinct roles in dealing with various stresses, forming a complex stress response system.

CONCLUSIONS

This study uncovered the conservation and divergence in cell types of leaves of upland cotton and sea-island cotton, which will provide a better understanding of phenotypic variation of the two species.

Distinct and redundant roles of the Arabidopsis OCTOPUS gene family in plant growth beyond phloem development

The Arabidopsis root apical meristem is an excellent model for studying plant organ growth. This involves a coordinated process of cell division, elongation, and differentiation, with each tissue type developing according to its own schedule. Among these tissues, the protophloem is particularly important, differentiating early to supply nutrients and signalling molecules to the growing root tip. The OCTOPUS (OPS) protein and its homologue OPS-LIKE 2 (OPL2) are essential for proper root protophloem differentiation and, probably through this role, indirectly promote root growth. Here, we explored the roles of the other three OPS homologues in Arabidopsis, OPL1, OPL3, and OPL4. OPS/OPL genes exhibited overlapping expression patterns and functions, with a high degree of redundancy among them. Although higher order mutants did not display more severe phloem defects, they exhibited significantly reduced root growth compared with the ops opl2 mutant. These results indicate a direct contribution of the investigated OPL genes to meristematic activity. While our focus was on root growth, the OPS/OPL gene family also plays a positive role in regulating shoot growth, emphasizing its broader impact on plant development. Furthermore, our analyses reiterate the central role of OPS and the phloem domain in controlling overall plant growth.

Early transcriptomic changes in cucumber and maize roots in response to FePO4 nanoparticles as a source of P and Fe

The use of nanoparticles as an alternative to traditional fertilizers, aiming at a more efficient use of nutrients, is a recently developed concept that requires a thorough understanding of the processes occurring in the soil-plant system. A crucial aspect in this framework is to decipher the plant responses to the unique characteristics of these materials. In this work, we aim at decoding the transcriptional responses of cucumber and maize roots to FePO4 nanoparticles applied as P and Fe sources, respectively. The results demonstrate that P and Fe supplied as nanoscale salts support plant nutrition with an efficiency comparable to that of ionic forms of the nutrients. This supposition is confirmed by transcriptomic profiles that show no significant upregulation of transcripts typically induced by deficiencies in P and Fe in cucumber and maize plants in which these nutrients were provided by FePO4 nanoparticles. The analysis further revealed that nanoparticles alter the expression of genes involved in root development and stress responses, effect that appeared to be independent on the nutritional status of the plants. Our data further underline the challenge to identify generalizable elements of the impact of nanomaterials on plant species, as responses are intimately linked to the type of nanomaterials and differ among plant species.

Maize ZmBES1/BZR1-4 recruits ZmTLP5 to regulate drought tolerance and seed development by regulating ZmPum6 and ZmMBP1

BES1/BZR1, a kind of plant-specific transcription factor (TF), has been reported to regulate growth, development, and stress response. However, the maize BES1/BZR1 members are still largely unknown. In this study, we investigated the function and regulatory mechanism of maize ZmBES1/BZR1-4 in regulating drought response and seed development. The ZmBES1/BZR1-4 was localized in the nucleus depending on its bHLH domain and showed no self-transactivation activity. The transcription level of ZmBES1/BZR1-4 was induced by drought stress and was predominantly higher in seeds 25 days after pollination. Overexpression of ZmBES1/BZR1-4 reduced drought tolerance but produced bigger seeds with higher seed weight in transgenic Arabidopsis, rice, and maize. Inversely, the ZmBES1/BZR1-4 mutant Mu4-1 and Mu4-2 showed enhancement of drought tolerance and decreased seed size and weight. The ZmBES1/BZR1-4 could directly bind to E-box elements in the ZmMBP1 and ZmPum6 promoters to activate their transcription. Furthermore, the interaction between ZmBES1/BZR1-4 and ZmTLP5 enhanced the ZmMBP1 and ZmPum6 transcription. Moreover, ZmMBP1 and ZmPum6 positively regulated seed size and weight, but ZmPum6 negatively regulated drought tolerance. Therefore, our findings reveal that ZmBES1/BZR1-4 recruits ZmTLP5 to regulate drought tolerance and seed development by regulating ZmMBP1 and ZmPum6, which contributes to uncovering the function of BES1/BZR1s regulating growth, development, and stress response in crops.

Deciphering the complex roles of leucine-rich repeat receptor kinases (LRR-RKs) in plant signal transduction

Leucine-rich repeat receptor kinases (LRR-RKs) are essential receptor protein kinases in plants that are the key to signal perception and responses and central to regulating plant growth, development, and defense. Despite extensive research on the LRR-RK family, gaps persist in our understanding of their ligand recognition and activation mechanisms, interactions with co-receptor, signal transduction pathways, and biochemical and molecular regulation. Researchers have made significant advances in understanding the critical roles of LRR-RKs in plant growth and development, signal transduction, and stress responses. Here, we first summarized the gene expression levels of LRR-RKs in plants. We then reviewed the conservation and evolutionary relationships of these genes across different species. We also investigated the molecular mechanisms underlying the variations in LRR-RK signaling under different environmental conditions. Finally, we provide a comprehensive summary of how abiotic and biotic stresses modulate LRR-RK signaling pathways in plants.

Suitable concentrations of brassinolide application enhances growth performance and saikosaponin biosynthesis by transcriptional activation of triterpenoid pathway genes in Bupleurum chinense DC

The role of brassinolides (BRs) in regulating the synthesis of plant secondary metabolites has been recognized. However, the effect of brassinolides on the synthesis of saikosaponin in Bupleurum chinense DC. (B. chinense) is still unresolved, To address this knowledge gap, experiments were conducted in which different concentrations (0 mg/L as CK, 0.1 mg/L, 0.2 mg/L, and 0.4 mg/L) of BRs solution were sprayed on B. chinense taproot in the present study. We measured the growth indicators of each group of B. chinense, used quantitative real-time PCR (qRT-PCR) to determine the expression level of genes related to the biosynthesis of saikosaponin, used terpenoid-targeted metabolomics to determine the accumulation of saikosaponin, and verified the metabolomics results by HPLC. Following a 12-day treatment with the 0.2 mg/L BRs solution, the fresh and dry root weights, the taproot length, and the taproot diameter of B. chinense escalated by 60.35%, 60.11%, 25.17%, and 28.07% respectively, in comparison with the CK group. The expression of genes related to the biosynthesis of saikosaponin (HMGR, DXR, IPPI, FPS, SE, P450-2, and P450-3) significantly increased. Moreover, a terpenoid-targeted metabolomic investigation identified 27 distinct saikosaponins, inclusive of saikosaponin A and D, with a notable accumulation observed in 17 saikosaponins. The HPLC findings indicated that the contents of saikosaponin A and D elevated by 72.64% and 80.75% respectively when treated with 0.2 mg/L BRs solution. Conversely, the treatment of 0.4 mg/L BRs solution did not exhibit any significant alteration in the concentrations of saikosaponin A and D when compared to the CK group. In conclusion, the 0.2 mg/L BRs solution demonstrates a more pronounced regulatory impact on the synthesis of saikosaponin A and D. Our investigation revealed that the accumulation of these crucial medicinal bioactive compounds, saikosaponin A and D, can be enhanced through the application of a 0.2 mg/L BRs solution in the ecological cultivation of B. chinense.

Increased chloroplast area in the rice bundle sheath through cell-specific perturbation of brassinosteroid signaling

In the leaves of C3 species such as rice (Oryza sativa), mesophyll cells contain the largest compartment of photosynthetically active chloroplasts. In contrast, plants that use the derived and more efficient C4 photosynthetic pathway have a considerable chloroplast compartment in both bundle sheath and mesophyll cells. Accordingly, the evolution of C4 photosynthesis from the ancestral C3 state required an increased chloroplast compartment in the bundle sheath. Here, we investigated the potential to increase chloroplast compartment size in rice bundle sheath cells by manipulating brassinosteroid signaling. Treatment with brassinazole, a brassinosteroid biosynthesis inhibitor, raised leaf chlorophyll content and increased the number but decreased the area of chloroplasts in bundle sheath cells. Ubiquitous overexpression of the transcription factor-encoding BRASSINAZOLE RESISTANT 1 (OsBZR1) increased bundle sheath chloroplast area by up to 45%, but these plants became chlorotic. However, when OsBZR1 expression was driven by a bundle sheath-specific promoter, the negative effects on growth and viability were alleviated while chloroplast area still increased. In summary, we report a role for brassinosteroids in controlling chloroplast area and number in rice and conclude that cell-specific manipulation of brassinosteroid signaling can be used to manipulate the chloroplast compartment in rice bundle sheath cells.

Genome Identification, Expression Profile Analysis, and Abiotic Stress Response Mechanism of Longan BES1 Gene

BES1 (BRI1 EMS SUPPRESSOR 1) is a critical transcription factor involved in plant growth, development, and stress responses. Although BES1 genes have been characterized in several species, their roles in longan (Dimocarpus longan Lour.) remain unclear. This study identified and analyzed eight BES1 genes in the longan genome. Phylogenetic analysis classified these genes into four subgroups (I-IV), with conserved motifs and intron-exon structures indicating potential functional similarities within subgroups. Cis-element analysis revealed that the promoters of DlBES1 genes contain numerous hormone-related elements, including ABRE, TGACG, and TCA motifs, suggesting their involvement in hormonal signaling and stress responses. Expression profiling showed differential expression patterns of DlBES1 genes across nine tissues, with notable up-regulation in roots and seeds. Additionally, DlBES1 genes exhibited distinct expression trends under varying temperatures and in response to IAA treatment, indicating potential roles in temperature stress adaptation and hormone signaling. These findings provide novel insights into the regulatory mechanisms of BES1 genes in longan and highlight their potential significance in stress tolerance and growth regulation.

Identification of Cysteine synthase (Cys) Gene Family in Tomato (Solanum lycopersicum) and Functional of SlCys5 in Cold Stress Tolerance

Sulfur is an intermediate element in plants. It plays an important role in the growth and development of plants. Plant roots absorb sulfate from their external environment and produce cysteine under the catalysis of cysteine synthase. Cysteine is a synthetic precursor of sulfur-containing metabolites and critical molecules including glutathione (GSH), methionine, vitamins, coenzymes, and antioxidants. It also plays a central role in plant stress resistance. In this study, we identified the Cys family genes in tomato and analyzed the expression of SlCys genes under cold stress. A bioinformatics analysis showed that the SlCys gene promoters were rich in cis-acting elements related to stress response. Transcriptome data analysis and qRT-PCR (real-time fluorescent quantitative polymerase chain reaction) experiments showed that SlCys5 may be the key gene in the Cys gene family for cold tolerance in tomato. After cold stress treatment, the SlCys5-silenced tomato plants were more sensitive to cold stress, and wilting was more severe than in control plants. Thus, SlCys5 is a positive regulator of cold tolerance in tomato. In this study, we elucidated the evolutionary pattern and functional differentiation of the Cys gene family in tomato, deepening our understanding of the regulatory mechanism of cold stress tolerance in plants.

Research on the regulation mechanism of drought tolerance in wheat

Wheat (Triticum aestivum L.) is one of the most important crops in arid and semi-arid areas of the world, and its sustainable and efficient production is essential for ensuring food security in China and globally. However, with the global climate change, wheat production is increasingly endangered by abiotic stress, and drought stress has become the main abiotic stress factor restricting wheat production efficiently. Therefore, investigating drought resistance genes and elucidating the mechanisms underlying drought resistance regulation is crucial for the genetic enhancement of drought resistance and the development of new drought-resistant wheat varieties. This paper reviews the majority of research conducted on wheat drought resistance over the past five years, focusing on aspects, such as transcriptional regulation, protein post-translational modifications, and other regulatory mechanisms related to drought resistance in wheat. Additionally, this paper discusses future directions for the genetic improvement of drought resistance and the breeding of new drought-resistant wheat varieties.

Root stem cell homeostasis in Arabidopsis involves cell-type specific transcription factor complexes

In Arabidopsis thaliana the root stem cell niche (SCN) is maintained by a complex regulatory network crucial for growth and developmental plasticity. However, many aspects of this network, particularly concerning stem cell quiescence and replenishment, remain unclear. Here, we investigate the interactions of key transcription factors (TFs) BRASSINOSTEROID AT VASCULAR AND ORGANIZING CENTRE (BRAVO), PLETHORA 3 (PLT3), and WUSCHEL-RELATED HOMEOBOX 5 (WOX5) in SCN maintenance. Analysis of mutants reveals their combinatorial regulation of cell fates and divisions in the SCN. In addition, studies using Fluorescence Resonance Energy Transfer Fluorescence Lifetime Imaging Microscopy (FRET-FLIM) in combination with novel analysis methods enable us to quantify protein-protein interaction (PPI) affinities and higher-order complex formation among these TFs. Our findings were integrated into a computational model, indicating that cell-type specific protein complex profiles and formations, influenced by prion-like domains in PLT3, play an important role in regulating the SCN. We propose that these unique protein complex signatures may serve as indicators of cell specificity, enriching the regulatory network that governs stem cell maintenance and replenishment in the Arabidopsis root.

Biosynthesis of triterpenoids in plants: Pathways, regulation, and biological functions

Plant triterpenoids, a vast and diverse group of natural compounds derived from six isoprene units, exhibit an extensive array of structural diversity and remarkable biological activities. In this review, we update the recent research progress in the catalytic mechanisms underlying triterpene synthesis and summarize the current insights into the biosynthetic pathways and regulatory mechanisms of triterpenoids. We emphasize the biosynthesis of pharmacologically active triterpenoids and the role of triterpenoid synthesis in plant growth, development, defense mechanisms, and plant-microbe interactions. This insight review offers a comprehensive perspective on the applications and future avenues of triterpenoid research.

ABCB transporters: functionality extends to more than auxin transportation

MAIN CONCLUSION

ABCs transport diverse compounds; with plant's most abundant ABCG and ABCB subfamilies. ABCBs are multi-functional transporter proteins having role in plant adaptation. ATP-binding cassette (ABC) proteins have been known for the transportation of various structurally diverse compounds in all kingdoms of life. Plants possess a particularly high number of ABC transporters compared to other eukaryotes: the most abundant being ABCG followed by the ABCB subfamilies. While members of the ABCB subfamily are primarily known for auxin transportation, however, studies have shown their involvement in variety of other functions viz. growth and development, biotic and abiotic stresses, metal toxicity and homeostasis, cellular redox state stability, stomatal regulation, cell shape maintenance, and transport of secondary metabolites and phytohormones. These proteins are able to perform various biological processes due to their widespread localization in the plasma membrane, mitochondrial membrane, chloroplast, and tonoplast facilitating membrane transport influenced by various environmental and biological cues. The current review compiles published insights into the role of ABCB transporters, and also provides brief insights into the role of ABCB transporters in a medicinal plant, where the synthesis of its bioactive secondary metabolite is linked to the primary function of ABCBs, i.e., auxin transport. The review discusses ABCB subfamily members as multi-functional protein and comprehensively examines their role in various biological processes that help plants to survive under unfavorable environmental conditions.

A glycogen synthase kinase-3 gene enhances grain yield heterosis in semi-dwarf rapeseed

Optimizing plant height is a key breeding objective in Brassica napus to enhance lodging resistance and increase yield potential. In the present study, we identified a semi-dwarf gene in rapeseed, BnDWARF5 (BnDF5), which encodes a glycogen synthase kinase 3, BRASSINOSTEROID-INSENSITIVE 2 (BnaC03.BIN2), primarily controlling the elongation of basal internodes by inhibiting the elongation of internode cells. Genetic mapping and cloning revealed that BnDF5 is governed by a semi-dominant/dominant gene located on chromosome C03. Sequencing uncovered an SNP in BnaC03.BIN2 due to an amino acid substitution, which was confirmed via kompetitive allele-specific polymerase chain reaction marker analysis, and expressing the mutated BnaC03.BIN2 in the wild type resulted in decreased plant height. Practical breeding applications showed that heterozygous BnDF5 plants exhibited optimal intermediate height and strong yield heterosis, making the semi-dwarf mutant a valuable genetic resource for developing semi-dwarf rapeseed varieties with improved lodging resistance and yield.

Genetic manipulations of brassinosteroid-related genes improve various agronomic traits and yield in cereals enabling new biotechnological revolution: Achievements and perspectives

Brassinosteroids (BRs) are steroid phytohormones which regulate various developmental and physiological processes throughout plant life cycle, from seed development and germination, up to modulation of reproduction and senescence. Importantly, mutants defective in the BR biosynthesis or response show various degree of plant height reduction (dwarfism or semi-dwarfism). This agronomic trait is of particular importance considering that in contrast to tall cereal varieties, semi-dwarf cereal plants are more tolerant to lodging which occurs during unfavorable weather conditions and constitutes a serious threat to plant reproduction and yield. Moreover, it was shown that the BR deficiency or insensitivity lead to erect stature of cereal plants what enables increase in planting density and yield. The valuable combinations of these traits make the BR-related mutants exceptional alternatives in breeding programs. Noteworthy, BRs play a noticeable role in regulation of grain/kernel shape and size. Therefore, these crucial agronomic traits may be manipulated specifically in BR-dependent manner. Importantly, the semi-dwarf mutants have been successfully introduced into cereal breeding programs in the past, and new semi-dwarf mutants developed through application of gene editing approach have been recently reported as promising alternatives for development of novel, high-yielding cereal cultivars. This review presents a comprehensive description of genetic manipulations of the BR-related genes aimed at improvements of various agronomic traits in the major cereal crops - rice, wheat, maize, and barley. These improvements may be achieved through application of panicle- or grain-specific promoters, overexpression or gain-of-function approaches, gene silencing, and targeted gene editing.

Regulatory variation controlling architectural pleiotropy in maize

An early event in plant organogenesis is establishment of a boundary between the stem cell containing meristem and differentiating lateral organ. In maize (Zea mays), evidence suggests a common gene network functions at boundaries of distinct organs and contributes to pleiotropy between leaf angle and tassel branch number, two agronomic traits. To uncover regulatory variation at the nexus of these two traits, we use regulatory network topologies derived from specific developmental contexts to guide multivariate genome-wide association analyses. In addition to defining network plasticity around core pleiotropic loci, we identify new transcription factors that contribute to phenotypic variation in canopy architecture, and structural variation that contributes to cis-regulatory control of pleiotropy between tassel branching and leaf angle across maize diversity. Results demonstrate the power of informing statistical genetics with context-specific developmental networks to pinpoint pleiotropic loci and their cis-regulatory components, which can be used to fine-tune plant architecture for crop improvement.

Mutations of the brassinosteroid biosynthesis gene HvDWARF5 enable balance between semi-dwarfism and maintenance of grain size in barley

Brassinosteroids (BRs) are phytohormones which regulate various developmental processes in plants. They are exceptional phytohormones, as they do not undergo long-distance transport between plant organs. However, knowledge about the function of the enzymes that catalyse BR biosynthesis (particularly its early stages) in cereal crops remains limited. Therefore, this study identifies and analyses the function of the HvDWARF5 (HvDWF5) gene, involved in the early stage of BR biosynthesis in barley (Hordeum vulgare), an important cereal crop, using the TILLING (Targeting Induced Local Lesions IN Genomes) approach. The detailed functional analysis allowed for the identification of various mutations in different gene fragments. The influence of these mutations on plant architecture, reproduction, and yield was characterised. Moreover, effects of the missense and intron retention mutations on sequence and splicing of the HvDWF5 transcript, sequence and predicted structure of the encoded HvDWF5 enzyme, and accumulation of endogenous BR were determined. Some of the barley mutants identified in this study showed semi-dwarfism, a trait of particular importance for cereal breeding and yield. However, unlike other BR mutants in cereals, this did not negatively affect grain size or weight. It indicated that mutations in this gene allow for a balance between plant height reduction and maintenance of grain size. Thus, the results of this study provide a novel insight into the role of the HvDWF5 gene in the BR biosynthesis-dependent regulation of architecture and reproduction of the important cereal crop - barley.

Signalling and regulation of plant development by carbon/nitrogen balance

The two most abundant macronutrients in plant cells are carbon (C) and nitrogen (N). Coordination of their cellular metabolism is a fundamental factor in guaranteeing the optimal growth and development of plants. N availability and assimilation profoundly affect plant gene expression and modulate root and stem architecture, thus affecting whole plant growth and crop yield. N status also affects C fixation, as it is an important component of the photosynthetic machinery in leaves. Reciprocally, increasing C supply promotes N uptake and assimilation. There is extensive knowledge of the different mechanisms that plants use for sensing and signalling their nutritional status to regulate the assimilation, metabolism and transport of C and N. However, the crosstalk between C and N pathways has received much less attention. Plant growth and development are greatly affected by suboptimal C/N balance, which can arise from nutrient deficiencies or/and environmental cues. Mechanisms that integrate and respond to changes in this specific nutritional balance have started to arise. This review will examine the specific responses to C/N imbalance in plants by focusing on the main inorganic and organic metabolites involved, how they are sensed and transported, and the interconnection between the early signalling components and hormonal networks that underlies plants' adaptive responses.

CsBZR1-CsCEL1 module regulates the susceptibility of cucumber to Meloidogyne incognita by mediating cellulose metabolism

Plant-parasitic root knot nematode is a pernicious menace to agriculture. Therefore, uncovering the mechanism of nematode infection is a critical task for crop improvement. Here, with cucumber as material, we found that CsCEL1, encoding β-1,4-endoglucanase to facilitate cellulose degradation, was profoundly induced in the root infected by Meloidogyne incognita. Intriguingly, suppressing the expression of CsCEL1 in cucumber conferred resistance to M. incognita infection with reduced activity of β-1,4-endoglucanase but promoted cellulose in the root. Conversely, overexpressing CsCEL1 in Arabidopsis increased the number of nematode-induced galls. These results suggest that CsCEL1 negatively regulates the resistance to M. incognita. Furthermore, we verified the transcriptional activation of CsCEL1 by CsBZR1, a key transcription factor involved in brassinosteroid signaling. Suppressing the expression of CsBZR1 in cucumber significantly reduced the size and number of galls and suppressed giant cell formation, with promoted cellulose content. Conversely, overexpressing CsBZR1 in Arabidopsis decreased resistance to M. incognita. Exogenous application of brassinosteroid to cucumber suppressed both CsCEL1 and CsBZR1 expressions, significantly reduced the gall numbers, thus improved resistance to M. incognita. Collectively, these results suggest that the CsBZR1-CsCEL1 module is implicated in modulating cellulose content, which may influence M. incognita infection. The finding provides novel insight into the molecular regulations of nematode resistance for breeding resistant varieties or nematode management.

WRKY transcription factors: Hubs for regulating plant growth and stress responses

As sessile organisms, plants must directly face various stressors. Therefore, plants have evolved a powerful stress resistance system and can adjust their growth and development strategies appropriately in different stressful environments to adapt to complex and ever-changing conditions. Nevertheless, prioritizing defensive responses can hinder growth; this is a crucial factor for plant survival but is detrimental to crop production. As such, comprehending the impact of adverse environments on plant growth is not only a fundamental scientific inquiry but also imperative for the agricultural industry and for food security. The traditional view that plant growth is hindered during defense due to resource allocation trade-offs is challenged by evidence that plants exhibit both robust growth and defensive capabilities through human intervention. These findings suggest that the growth‒defense trade-off is not only dictated by resource limitations but also influenced by intricate transcriptional regulatory mechanisms. Hence, it is imperative to conduct thorough investigations on the central genes that govern plant resistance and growth in unfavorable environments. Recent studies have consistently highlighted the importance of WRKY transcription factors in orchestrating stress responses and plant-specific growth and development, underscoring the pivotal role of WRKYs in modulating plant growth under stressful conditions. Here, we review recent advances in understanding the dual roles of WRKYs in the regulation of plant stress resistance and growth across diverse stress environments. This information will be crucial for elucidating the intricate interplay between plant stress response and growth and may aid in identifying gene loci that could be utilized in future breeding programs to develop crops with enhanced stress resistance and productivity.

VvATG18a participates in grape resistance to gray mold induced by BR signaling pathway

Autophagy plays an important role in responding to necrotrophic pathogens and plant signal hormones. Brassinosteroids (BRs) are a class of natural steroidal phytohormones that effectively regulated the disease resistance responses in grape. However, the molecular mechanism of BR-autophagy networks responsible for activation of host defense against gray mold remained to be elucidated. We reported a novel defense mechanism that BR-regulated autophagy in grape berry against gray mold. Exogenous application of 24-epibrassinolide (eBR) enhanced the grape disease resistance. Meanwhile, the endogenous BR was accumulated and BR signaling pathway was activated in the berries. In addition, transcriptome analysis in eBR-treated grapes infected with gray mold showed that the differentially expressed genes (DEGs) were enriched in the metabolic pathway of BR signaling pathway and autophagy. DNA affinity purification sequencing (Dap-seq), Yeast one-hybrid assay (Y1H) and dual luciferase assays (LUC) verified VvBZR1 bound to the promoter of VvATG18a to induce its gene expression. Overexpressing VvATG18a and VvBZR1 improved the resistance of grapes to gray mold. Overall, this study sheds light on the immune mechanisms underlying the involvement of the autophagy in grape innate immunity, highlighting the pivotal role of VvATG18a in enhancing disease resistance.

Understanding brassinosteroid-centric phytohormone interactions for crop improvement

Brassinosteroids (BRs) play a crucial role in regulating multiple biological processes in plants, particularly those related to crop productivity and stress tolerance. During their functioning, BRs engage in extensive and intricate interactions with other phytohormones, including auxin, cytokinins, gibberellins, abscisic acid, ethylene, jasmonates, salicylic acid, and strigolactones. These interactions facilitate the integration of internal and external signals, ultimately shaping the physiological status of the plant. In this review, we introduce BR metabolism and signaling and discuss their role in modulating agronomic traits that directly contribute to grain yield in rice (Oryza sativa), the model plant for crops. We also summarize recent advances in the crosstalk between BRs and other phytohormones in regulating agronomic traits in crops. Furthermore, we highlight significant research that provides insights into developing high-yielding and stress-resistant crop varieties from the perspective of hormone crosstalk. Understanding the genetic and molecular mechanisms through which BRs and other phytohormones collaboratively control agronomic traits offers new approaches for crop improvement.

Crucial Roles of Brassinosteroids in Cell Wall Composition and Structure Across Species: New Insights and Biotechnological Applications

Brassinosteroids (BR) are steroidal phytohormones essential for plant growth, development, and stress resistance. They fulfil this role partially by modulating cell wall structure and composition through the control of gene expression involved in primary and secondary cell wall biosynthesis and metabolism. This affects the deposition of cellulose, lignin, and other components, and modifies the inner architecture of the wall, allowing it to adapt to the developmental status and environmental conditions. This review focuses on the effects that BR exerts on the main components of the cell wall, cellulose, hemicellulose, pectin and lignin, in multiple and relevant plant species. We summarize the outcomes that result from modifying cell wall components by altering BR gene expression, applying exogenous BR and utilizing natural variability in BR content and describing new roles of BR in cell wall structure. Additionally, we discuss the potential use of BR to address pressing needs, such as increasing crop yield and quality, enhancing stress resistance and improving wood production through cell wall modulation.

GOLEM: A tool for visualizing the distribution of Gene regulatOry eLEMents within the plant promoters with a focus on male gametophyte

Gene expression regulation during tissue development is extremely complex. A key mechanism of gene regulation is the recognition of regulatory motifs, also known as cis-regulatory elements (CREs), by various proteins in gene promoter regions. Localization of these motifs near the transcription start site (TSS) or translation start site (ATG) is crucial for transcription initiation and rate. Transcription levels of individual genes, regulated by these motifs, can vary significantly across tissues and developmental stages, especially in processes like sexual reproduction. However, the precise localization and visualization of these motifs in relation to gene expression in specific tissues can be challenging. Here, we introduce a freely available tool called GOLEM (Gene regulatOry eLEMents; https://golem.ncbr.muni.cz), which enables users to precisely locate any motif of interest with respect to TSS or ATG within the relevant plant genomes across the plant Tree of Life (Chara, Marchantia, Physcomitrium, Azolla, Ceratopteris, Amborella, Oryza, Zea, Solanum and Arabidopsis). The visualization of the motifs is performed with respect to the transcript levels of particular genes in leaves and male reproductive tissues and can be compared with genome-wide distribution regardless of the transcription level. Additionally, genes with specific CREs at defined positions and high expression in selected tissues can be exported for further analysis. GOLEM's functionality is illustrated by its application to conserved motifs (e.g. TATA-box, ABRE, I-box, and TC-element), hormone-responsive elements (GCC-box, ARR10_binding motif), as well as to male gametophyte-related motifs (e.g., LAT52, MEF2, and DOF_core).

CmbZIP19 inhibits lateral bud elongation via the brassinolide pathway in chrysanthemum

Branching is the main factor that determines plant architecture and is closely related to plant adaptation to the environment. Cold stress can inhibit lateral bud elongation in plants, but the underlying mechanism is still unclear. Here, we report that the cold stress-induced bZIP family transcription factor CmbZIP19 inhibits lateral bud elongation in chrysanthemum. We identified the target gene of CmbZIP19 as the brassinolide (BR) synthesis-related gene CmDWF1 by integrating RNA-seq and DAP-seq data. CmbZIP19 can directly bind to the ZDRE-like motif in the promoter region of CmDWF1, thereby inhibiting the expression of CmDWF1. We confirmed that CmDWF1 can promote the lateral branch elongation of chrysanthemum by genetic transformation. The branching phenotype of CmbZIP19-RNAi plants could be restituted by BR treatment. Taken together, the results suggest that CmbZIP19 modulates plant architecture by suppressing BR synthesis.

The phytohormone brassinosteroid (BR) promotes early seedling development via auxin signaling pathway in rapeseed

The phytohormone brassinosteroid (BR) regulate various developmental and physiological processes in plants. However, the function of BR during early seedling development stage in rapeseed is largely unknown. To understand the effects of exogenous BR during early seedling development, the ZS11 and BR-INSENSITIVE (bin2) mutants were treated with BR before seed sowing and seed germination stage under 16/8 hours light/dark cycle. The phenotype results indicated that BR promotes only seedling establishment but not seed germination stage in ZS11, while no function in bin2 mutants. Since BRs play a crucial role in regulation of developmental transition between growth in the dark (skotomorphogenesis) and growth in the light (photomorphogenesis), the ZS11 and bin2 mutants were treated with BR under continuous light and dark. The BR treatment also showed the same functions as 16/8 hours light/dark cycle. To understand the function of BR on expression levels, the differentially expressed genes (DEGs) and differentially expressed metabolites (DEMs) between mock- and BR-treated seedlings were explored. A total of 234 significantly DEGs were identified between the mock- and BR-treated groups by transcriptomic analyses. These DEGs were markedly enriched in BR biosynthesis, pentose and glucuronate interconversions and plant hormone signal transduction pathways. Meanwhile, a total of 145 DEMs were identified through metabolomics analyses, with a significant enrichment in lipid substances. Interestingly, some genes and metabolites associated with auxin pathway were identified, which exhibited up-regulation in both DEGs and DEMs after BR treatment. Subsequently, functional enrichment analyses revealed that the majority of DEGs and DEMs were primarily enriched in ascorbate and aldehyde metabolism, arginine and proline metabolism, tryptophan metabolism (the main route for auxin synthesis) and cyanogenic amino acid metabolism. Furthermore, it was found that glutamate was up-regulated in nitrogen metabolism, glyoxylate and dicarboxylate metabolism, and arginine and proline metabolism pathways. These indicated that the glutamate signaling pathway was a key regulatory pathway for exogenous BR to induce seedling establishment. These evidence implied that exogenous BR treatment lead to up-regulation of auxin-related genes expression, then promoted seedling establishment in rapeseed.

Brassinosteroids in Micronutrient Homeostasis: Mechanisms and Implications for Plant Nutrition and Stress Resilience

Brassinosteroids (BRs) are crucial plant hormones that play a significant role in regulating various physiological processes, including micronutrient homeostasis. This review delves into the complex roles of BRs in the uptake, distribution, and utilization of essential micronutrients such as iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), and boron (B). BRs influence the expression of key transporter genes responsible for the absorption and internal distribution of these micronutrients. For iron, BRs enhance the expression of genes related to iron reduction and transport, improve root architecture, and strengthen stress tolerance mechanisms. Regarding zinc, BRs regulate the expression of zinc transporters and support root development, thereby optimizing zinc uptake. Manganese homeostasis is managed through the BR-mediated regulation of manganese transporter genes and chlorophyll production, essential for photosynthesis. For copper, BRs influence the expression of copper transporters and maintain copper-dependent enzyme activities crucial for metabolic functions. Finally, BRs contribute to boron homeostasis by regulating its metabolism, which is vital for cell wall integrity and overall plant development. This review synthesizes recent findings on the mechanistic pathways through which BRs affect micronutrient homeostasis and discusses their implications for enhancing plant nutrition and stress resilience. Understanding these interactions offers valuable insights into strategies for improving micronutrient efficiency in crops, which is essential for sustainable agriculture. This comprehensive analysis highlights the significance of BRs in micronutrient management and provides a framework for future research aimed at optimizing nutrient use and boosting plant productivity.

CmCYC2d is a Regulator of Leaf Abaxial Curling in Chrysanthemum morifolium

Leaf morphology is crucial for plant photosynthesis and stress adaptation. While CIN-like TCP transcription factors are well-known for their roles in leaf curling and morphogenesis, the function of CYC-like TCPs in leaf development remains largely unexplored. This study identifies CmCYC2d as a key regulator of abaxial leaf curling in Chrysanthemum morifolium. Phenotypic analysis revealed that the downward curling observed in OX-CmCYC2d transgenic lines was primarily due to the enlargement of adaxial epidermal cells. Furthermore, a reduction in epidermal cell number was identified as a significant contributor to the smaller leaf area in these plants. Transcriptome and WGCNA analyses highlighted CmSAUR55 as a potential downstream target of CmCYC2d. ChIP-qPCR, EMSA, and LUC assays confirmed that CmCYC2d directly bound to the CmSAUR55 promoter. Additionally, transcriptome data revealed that the reduced cell number in OX-CmCYC2d transgenic lines may be mediated by auxin-related pathways and key genes such as CNR7. The CmCYC2d-CmSAUR55 module was also closely linked to the development of enlarged adaxial epidermal cells in the leaf sinus, emphasising its role in this developmental process. This study highlights the regulatory role of CmCYC2d in leaf development and sheds light on the molecular mechanisms underlying leaf curling in chrysanthemum.

BRASSINAZOLE RESISTANT 1 delays photoperiodic flowering by repressing CONSTANS transcription

Photoperiodic regulation of flowering time plays a critical role in plant reproductive success and crop yield. In Arabidopsis thaliana, the expression of the CONSTANS (CO) gene is closely regulated by day length and is modulated by both environmental and endogenous cues for precise control over flowering. Our findings reveal that the phytohormone brassinosteroid (BR) pathway represses flowering by inhibiting the expression of both CO and Flowering Locus T (FT). Additionally, we discovered that BRASSINAZOLE RESISTANT 1 (BZR1), a key transcription factor in the BR signaling pathway, directly binds to the proximal promoter region of CO to suppress its transcription during long days, thus regulating photoperiodic flowering. Genetically, BZR1 acts upstream of CO and FT to delay floral initiation depending on day length. Overall, our study reveals how a molecular module comprising BZR1-CO integrates signals from BR as well as photoperiodicity for appropriate adjustment of flowering time.

The transcription factor SlLBD40 regulates seed germination by inhibiting cell wall remodeling enzymes during endosperm weakening

Uniform seed germination is crucial for consistent seedling emergence and efficient seedling production. In this study, we identified a seed-expressed protein in tomato (Solanum lycopersicum), lateral organ boundaries domain 40 (SlLBD40), that regulates germination speed. CRISPR/Cas9-generated SlLBD40 knockout mutants exhibited faster germination due to enhanced seed imbibition, independent of the seed coat. The expression of SlLBD40 was induced during the imbibition process, particularly in the micropylar endosperm, suggesting its role in endosperm weakening. Gene ontology analysis of RNA-seq data indicated that differentially expressed genes were enriched in cell wall-related processes. SlLBD40 directly targeted genes encoding cell wall remodeling enzymes implicated in endosperm weakening, including expansin 6 (SlEXP6), xyloglucan endotransglucosylase/hydrolase 23 (SlXTH23), and endo-β-mannanase 1 (SlMAN1). Our findings shed light on the role of endosperm weakening in regulating seed germination and propose potential gene targets for improving germination in species constrained by endosperm strength.

BvBZR1 improves parenchyma cell development and sucrose accumulation in sugar beet (Beta vulgaris L.) taproot

BRASSINAZOLE-RESISTANT (BZR) transcription factors, key elements of brassinolide (BR) signal transduction, play an important role in regulating plant growth and development. However, little is known about the molecular regulatory mechanism of BZR in sugar beet taproot growth. In this study, BvBZR1 expression was significantly induced by exogenous BR treatment. Transgenic sugar beet overexpressing BvBZR1 exhibited a higher taproot diameter compared with the wild type, mainly due to a significant enhancement in the spacing between cambial rings by increasing the size and layers of parenchyma cells. BvBZR1 regulated the expression of BvCESA6, BvXTH33, BvFAD3, and BvCEL1 and enhanced cell wall metabolism to promote sugar beet taproot growth in parenchyma cells and the development of each cambium ring. In addition, BvBZR1 overexpression significantly increased the accumulation of sucrose and soluble sugars in the taproot, which was attributed to its ability to regulate the expression of BvSPS and BvINV and improve the activity of BvSPS, BvSS-S, BvSS-C, and BvINV enzymes in each cambium ring and parenchyma cell in the sugar beet taproot. These results suggest that BvBZR1 can regulate the expression of genes related to cell wall and sucrose metabolism, improve corresponding enzyme activity, and promote the development of each cambium ring and parenchyma cell, thereby promoting the growth and development of sugar beet taproots.

GSK3s promote the phyB-ELF3-HMR complex formation to regulate plant thermomorphogenesis

Although elevated ambient temperature causes many effects on plant growth and development, the mechanisms of plant high-ambient temperature sensing remain unknown. In this study, we show that GLYCOGEN SYNTHASE KINASE 3s (GSK3s) negatively regulate high-ambient temperature response and oligomerize upon high-temperature treatment. We demonstrate that GSK3 kinase BIN2 specifically interacts with the high-temperature sensor phytochrome B (phyB) but not the high-temperature sensor EARLY FLOWER 3 (ELF3) to phosphorylate and promote phyB photobody formation. Furthermore, we show that phosphorylation of phyB by GSK3s promotes its interaction with ELF3. Subsequently, we find that ELF3 recruits the phyB photobody facilitator HEMERA (HMR) to promote its association with phyB. Taken together, our data reveal a mechanism that GSK3s promote the phyB-ELF3-HMR complex formation in regulating plant thermomorphogenesis.

Dual regulation of stomatal development by brassinosteroid in Arabidopsis hypocotyls

Stomata are epidermal pores that are essential for water evaporation and gas exchange in plants. Stomatal development is orchestrated by intrinsic developmental programs, hormonal controls, and environmental cues. The steroid hormone brassinosteroid (BR) inhibits stomatal lineage progression by regulating BIN2 and BSL proteins in leaves. Notably, BR is known to promote stomatal development in hypocotyls as opposed to leaves; however, its molecular mechanism remains elusive. Here, we show that BR signaling has a dual regulatory role in controlling stomatal development in Arabidopsis hypocotyls. We found that brassinolide (BL; the most active BR) regulates stomatal development differently in a concentration-dependent manner. At low and moderate concentrations, BL promoted stomatal formation by upregulating the expression of SPEECHLESS (SPCH) and its target genes independently of BIN2 regulation. In contrast, high concentrations of BL and bikinin, which is a specific inhibitor of BIN2 and its homologs, significantly reduced stomatal formation. Genetic analyses revealed that BIN2 regulates stomatal development in hypocotyls through molecular mechanisms distinct from the regulatory mechanism of the cotyledons. In hypocotyls, BIN2 promoted stomatal development by inactivating BZR1, which suppresses the expression of SPCH and its target genes. Taken together, our results suggest that BR precisely coordinates the stomatal development of hypocotyls using an antagonistic control of SPCH expression via BZR1-dependent and BZR1-independent transcriptional regulation.

Genome-Wide Identification and Characterization of the BZR Transcription Factor Gene Family in Leymus chinensis

BACKGROUND/OBJECTIVES

The BZR gene family, a critical transcription factor in the brassinosteroid (BR) signaling pathway, regulates plant growth and development. Despite its significance, the BZR gene family in Leymus chinensis, a valuable forage grass renowned for its stress tolerance and nutritional quality, remains uncharacterized, and its functional roles are largely unexplored.

METHODS

Employing advanced bioinformatics tools, we conducted a genome-wide survey to identify members of the BZR gene family in L. chinensis. Phylogenetic analyses were performed to classify these genes into distinct clades, while gene structure and conserved motif analyses assessed their evolutionary conservation and potential regulatory mechanisms. Additionally, transcriptome sequencing was utilized to examine the expression patterns of BZR genes in response to simulated animal grazing.

RESULTS

Eight LcBZR genes were identified, evenly distributed across all seven chromosomes. Phylogenetic analysis categorized these genes into three distinct groups, reflecting their evolutionary relationships. Most LcBZR genes exhibited highly conserved gene structures and motifs, with promoters enriched in cis-acting elements such as G-box and ARE. Expression profiling revealed that LcBZR genes are predominantly expressed in key tissues, particularly leaves and roots, suggesting their involvement in critical physiological processes. Transcriptomic analysis demonstrated that simulated animal grazing modulated the expression levels of LcBZR genes, implicating their role in promoting cellular elongation and division through the BR signaling pathway.

CONCLUSIONS

This study highlights the crucial role of LcBZR genes in regulating plant growth, development, and response to environmental stimuli, providing a foundational basis for understanding the molecular mechanisms of BR-mediated plant development and stress adaptation.

Structural insights into brassinosteroid export mediated by the Arabidopsis ABC transporter ABCB1

Brassinosteroids (BRs) are steroidal phytohormones indispensable for plant growth, development, and responses to environmental stresses. The export of bioactive BRs to the apoplast is essential for BR signaling initiation, which requires binding of a BR molecule to the extracellular domains of the plasma membrane-localized receptor complex. We have previously shown that the Arabidopsis thaliana ATP-binding cassette (ABC) transporter ABCB19 functions as a BR exporter and, together with its close homolog ABCB1, positively regulates BR signaling. Here, we demonstrate that ABCB1 is another BR transporter. The ATP hydrolysis activity of ABCB1 can be stimulated by bioactive BRs, and its transport activity was confirmed in proteoliposomes and protoplasts. Structures of ABCB1 were determined in substrate-unbound (apo), brassinolide (BL)-bound, and ATP plus BL-bound states. In the BL-bound structure, BL is bound to the hydrophobic cavity formed by the transmembrane domain and triggers local conformational changes. Together, our data provide additional insights into ABC transporter-mediated BR export.

Dressed Up to the Nines: The Interplay of Phytohormones Signaling and Redox Metabolism During Plant Response to Drought

Plants must effectively respond to various environmental stimuli to achieve optimal growth. This is especially relevant in the context of climate change, where drought emerges as a major factor globally impacting crops and limiting overall yield potential. Throughout evolution, plants have developed adaptative strategies for environmental stimuli, with plant hormones and reactive oxygen species (ROS) playing essential roles in their development. Hormonal signaling and the maintenance of ROS homeostasis are interconnected, playing indispensable roles in growth, development, and stress responses and orchestrating diverse molecular responses during environmental adversities. Nine principal classes of phytohormones have been categorized: auxins, brassinosteroids, cytokinins, and gibberellins primarily oversee developmental growth regulation, while abscisic acid, ethylene, jasmonic acid, salicylic acid, and strigolactones are the main orchestrators of environmental stress responses. Coordination between phytohormones and transcriptional regulation is crucial for effective plant responses, especially in drought stress. Understanding the interplay of ROS and phytohormones is pivotal for elucidating the molecular mechanisms involved in plant stress responses. This review provides an overview of the intricate relationship between ROS, redox metabolism, and the nine different phytohormones signaling in plants, shedding light on potential strategies for enhancing drought tolerance for sustainable crop production.

Time-Course Transcriptomics Analysis Reveals Molecular Mechanisms of Salt-Tolerant and Salt-Sensitive Cotton Cultivars in Response to Salt Stress

Salt stress is an environmental factor that limits plant seed germination, growth, and survival. We performed a comparative RNA sequencing transcriptome analysis during germination of the seeds from two cultivars with contrasting salt tolerance responses. A transcriptomic comparison between salt-tolerant cotton cv Jin-mian 25 and salt-sensitive cotton cv Su-mian 3 revealed both similar and differential expression patterns between the two genotypes during salt stress. The expression of genes related to aquaporins, kinases, reactive oxygen species (ROS) scavenging, trehalose biosynthesis, and phytohormone biosynthesis and signaling that include ethylene (ET), gibberellin (GA), abscisic acid (ABA), jasmonic acid (JA), and brassinosteroid (BR) were systematically investigated between the cultivars. Despite the involvement of these genes in cotton's response to salt stress in positive or negative ways, their expression levels were mostly similar in both genotypes. Interestingly, a PXC2 gene (Ghir_D08G025150) was identified, which encodes a leucine-rich repeat receptor-like protein kinase (LRR-RLK). This gene showed an induced expression pattern after salt stress treatment in salt-tolerant cv Jin-mian 25 but not salt-sensitive cv Su-mian 3. Our multifaceted transcriptome approach illustrated a differential response to salt stress between salt-tolerant and salt-sensitive cotton.

Crop root system architecture in drought response

Drought is a natural disaster that profoundly impacts on global agricultural production, significantly reduces crop yields, and thereby poses a severe threat to worldwide food security. Addressing the challenge of effectively improving crop drought resistance (DR) to mitigate yield loss under drought conditions is a global issue. An optimal root system architecture (RSA) plays a pivotal role in enhancing the capacity of crops to efficiently uptake water and nutrients, which consequently strengthens their resilience against environmental stresses. In this review, we discuss the compositions and roles of crop RSA and summarize the most recent developments in augmenting drought tolerance in crops by manipulating RSA-related genes. Based on the current research, we propose the potential optimal RSA configuration that could be helpful in enhancing crop DR. Lastly, we discuss the existing challenges and future directions for breeding crops with enhanced DR capabilities through genetic improvements targeting RSA.

BIL7 enhances plant growth by regulating the transcription factor BIL1/BZR1 during brassinosteroid signaling

Brassinosteroids (BRs) are plant steroid hormones that regulate plant development and environmental responses. BIL1/BZR1, a master transcription factor that regulates approximately 3000 genes in the BR signaling pathway, is transported to the nucleus from the cytosol in response to BR signaling; however, the molecular mechanism underlying this process is unknown. Here, we identify a novel BR signaling factor, BIL7, that enhances plant growth and positively regulates the nuclear accumulation of BIL1/BZR1 in Arabidopsis thaliana. BIL7-overexpressing plants were resistant to the BR biosynthesis inhibitor Brz and taller than wild-type (WT) plants were due to increased cell division. BIL7 is mainly localized to the plasma membrane, but during the early stages of cell growth, it was also localized to the nucleus. BIL7 was directly phosphorylated by the kinase BIN2, and nuclear localization of BIL7 was enhanced by the BIN2 inhibitor bikinin. BIL7 was found to bind to BIL1/BZR1, and nuclear accumulation of BIL1/BZR1 was strongly enhanced by BIL7 overexpression. Finally, double overexpression of BIL1/BZR1 and BIL7 led to greatly elongated hypocotyls in the presence of Brz. These findings suggest that BIL7 mediates nuclear accumulation of BIL1/BZR1, which activates inflorescence elongation in plants via BR signaling.

The miR3367-lncRNA67-GhCYP724B module regulates male sterility by modulating brassinosteroid biosynthesis and interacting with Aorf27 in Gossypium hirsutum

Cytoplasmic male sterile (CMS) lines play a crucial role in utilization of heterosis in crop plants. However, the mechanism underlying the manipulation of male sterility in cotton by long non-coding RNA (lncRNA) and brassinosteroids (BRs) remains elusive. Here, using an integrative approach combining lncRNA transcriptomic profiles with virus-induced gene silencing experiments, we identify a flower bud-specific lncRNA in the maintainer line 2074B, lncRNA67, negatively modulating with male sterility in upland cotton (Gossypium hirsutum). lncRNA67 positively regulates cytochrome P274B (GhCYP724B), which acted as an eTM (endogenous target mimic) for miR3367. The suppression of GhCYP724B induced symptoms of BR deficiency and male semi-sterility in upland cotton as well as in tobacco, which resulted from a reduction in the endogenous BR contents. GhCYP724B regulates BRs synthesis by interacting with GhDIM and GhCYP90B, two BRs biosynthesis proteins. Additionally, GhCYP724B suppressed a unique chimeric open reading frame (Aorf27) in 2074A mitochondrial genome. Ectopic expression of Aorf27 in yeast inhibited cellular growth, and over expression of Aorf27 in tobacco showed male sterility. Overall, the results proved that the miR3367-lncRNA67-GhCYP724B module positively regulates male sterility by modulating BRs biosynthesis. The findings uncovered the function of lncRNA67-GhCYP724B in male sterility, providing a new mechanism for understanding male sterility in upland cotton.

Hormonal regulation and crosstalk during early endosperm and seed coat development

KEY MESSAGE

This review covers the latest developments on the regulation of early seed development by phytohormones. The development of seeds in flowering plants starts with the fertilization of the maternal gametes by two paternal sperm cells. This leads to the formation of two products, embryo and endosperm, which are surrounded by a tissue of maternal sporophytic origin, called the seed coat. The development of each of these structures is under tight genetic control. Moreover, several phytohormones have been shown to modulate the development of all three seed compartments and have been implicated in the communication between them. This is particularly relevant, as embryo, endosperm, and seed coat have to coordinate their development for successful seed formation. Here, we review the latest advances on the hormonal regulation of early seed development in the model plant species Arabidopsis thaliana, with a focus on the endosperm and the seed coat. Moreover, we highlight how phytohormones serve as mechanisms of non-cell autonomous communication between these two compartments and how they are determinant in shaping seed formation.

Take a deep BReath: Manipulating brassinosteroid homeostasis helps cereals adapt to environmental stress

Global climate change leads to the increased occurrence of environmental stress (including drought and heat stress) during the vegetative and reproductive stages of cereal crop development. Thus, more attention should be given to developing new cereal cultivars with improved tolerance to environmental stress. However, during the development of new stress-tolerant cereal cultivars, the balance between improved stress responses (which occur at the expense of growth) and plant yield needs to be maintained. Thus, the urgent need for developing new cereal germplasm with improved stress tolerance could be fulfilled using semidwarf cereal mutants defective in brassinosteroid (BR) biosynthesis or signaling. BRs are steroid phytohormones that regulate various developmental and physiological processes throughout the plant life cycle. Mutants defective in BR biosynthesis or responses show reduced plant height (dwarfism or semi-dwarfism). Importantly, numerous reports indicate that genetic modification or biotechnological manipulation of BR biosynthesis or signaling genes in cereals such as rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), and barley (Hordeum vulgare), which are of crucial importance for global agriculture, may facilitate the development of cereal germplasm with improved stress tolerance. This review presents a comprehensive overview of the genetic manipulation of BR homeostasis in the above-mentioned cereal crops aimed at improving plant responses to various environmental stresses, such as drought, salinity, oxidative stress, thermal stress, and biotic stresses. We highlight target BR-related genes and the effects of genetic manipulation (gene editing, overexpression, and silencing or microRNA-mediated regulation) on plant adaptability to various stresses and provide future perspectives.