Recent advances in brassinosteroid biosynthetic pathway: insight into novel brassinosteroid shortcut pathway

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.

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.

Brassinosteroids mediate arbuscular mycorrhizal symbiosis through multiple potential pathways and partial identification in tomato

Currently, little is known regarding the specific processes through which brassinosteroids (BR) affect arbuscular mycorrhizal (AM) symbiosis. Understanding this relationship is vital for advancing plant physiology and agricultural applications. In this study, we aimed to elucidate the regulatory mechanisms of BR in AM symbiosis. According to the log2 fold change-value and adjP-value, we integrated the common differentially expressed genes (DEGs) in maize (Zea mays L.) treated with BR and AM, Arabidopsis (Arabidopsis thaliana) mutants deficient in BR receptors, and tomato (Solanum lycopersicum) plants inoculated with AM fungi. In addition, we characterized the symbiotic performance of tomato plants with BR receptor defects and overexpression. The results indicated that the common differential genes induced by BR and AM were involved in metabolic processes, such as cell wall modification, cytoskeleton remodeling, auxin and ethylene signaling, photosynthesis, mineral nutrient transport, and stress defense. Specifically, these include the BR1 gene, which modifies the cell wall. However, the fungal colonization rate of BR receptor-deficient tomato plants was significantly reduced, and the total phosphorus concentration was increased. Conversely, the performance of the overexpressing tomato transformation plants demonstrated a significant contrast. Additionally, the mild rescue of mycorrhizal attenuation in mutants treated with exogenous BR suggests the possibility of direct feedback from BR synthesis to AM. Notably, the cell wall modification gene (SlBR1) and calcium spike gene (SlIPD3) were induced by both BR and AM, suggesting that BR may influence cell penetration during the early stages of AM colonization. Synthesis: Our results demonstrated that BR positively regulates AM symbiosis through multiple pathways. These findings pave the way for future research, including isolation of the individual contributions of each pathway to this complex process and exploration of possible agricultural applications.

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.

Brassinosteroid biosynthesis and signaling: Conserved and diversified functions of core genes across multiple plant species

Brassinosteroids (BRs) are important regulators that control myriad aspects of plant growth and development, including biotic and abiotic stress responses, such that modulating BR homeostasis and signaling presents abundant opportunities for plant breeding and crop improvement. Enzymes and other proteins involved in the biosynthesis and signaling of BRs are well understood from molecular genetics and phenotypic analysis in Arabidopsis thaliana; however, knowledge of the molecular functions of these genes in other plant species, especially cereal crop plants, is minimal. In this manuscript, we comprehensively review functional studies of BR genes in Arabidopsis, maize, rice, Setaria, Brachypodium, and soybean to identify conserved and diversified functions across plant species and to highlight cases for which additional research is in order. We performed phylogenetic analysis of gene families involved in the biosynthesis and signaling of BRs and re-analyzed publicly available transcriptomic data. Gene trees coupled with expression data provide a valuable guide to supplement future research on BRs in these important crop species, enabling researchers to identify gene-editing targets for BR-related functional studies.

Genomic Insights into High-Altitude Adaptation: A Comparative Analysis of Roscoea alpina and R. purpurea in the Himalayas

Environmental stress at high altitudes drives the development of distinct adaptive mechanisms in plants. However, studies exploring the genetic adaptive mechanisms of high-altitude plant species are scarce. In the present study, we explored the high-altitude adaptive mechanisms of plants in the Himalayas through whole-genome resequencing. We studied two widespread members of the Himalayan endemic alpine genus Roscoea (Zingiberaceae): R. alpina (a selfing species) and R. purpurea (an outcrossing species). These species are distributed widely in the Himalayas with distinct non-overlapping altitude distributions; R. alpina is distributed at higher elevations, and R. purpurea occurs at lower elevations. Compared to R. purpurea, R. alpina exhibited higher levels of linkage disequilibrium, Tajima's D, and inbreeding coefficient, as well as lower recombination rates and genetic diversity. Approximately 96.3% of the genes in the reference genome underwent significant genetic divergence (FST ≥ 0.25). We reported 58 completely divergent genes (FST = 1), of which only 17 genes were annotated with specific functions. The functions of these genes were primarily related to adapting to the specific characteristics of high-altitude environments. Our findings provide novel insights into how evolutionary innovations promote the adaptation of mountain alpine species to high altitudes and harsh habitats.

Antifungal triazoles affect key non-target metabolic pathways in Solanum lycopersicum L. plants

Several 1,2,4-triazoles are widely used as systemic fungicides in agriculture because they inhibit fungal 14ɑ-demethylase. However, they can also act on many non-target plant enzymes, thereby affecting phytohormonal balance, free amino acid content, and adaptation to stress. In this study, tomato plants (Solanum lycopersicum L. var. 'Cherrola') were exposed to penconazole, tebuconazole, or their combination, either by foliar spraying or soil drenching, every week, as an ecotoxicological model. All triazole-exposed plants showed a higher content (1.7-8.8 ×) of total free amino acids than the control, especially free glutamine and asparagine were increased most likely in relation to the increase in active cytokinin metabolites 15 days after the first application. Conversely, the Trp content decreased in comparison with control (0.2-0.7 ×), suggesting depletion by auxin biosynthesis. Both triazole application methods slightly affected the antioxidant system (antioxidant enzyme activity, antioxidant capacity, and phenolic content) in tomato leaves. These results indicated that the tomato plants adapted to triazoles over time. Therefore, increasing the abscisic and chlorogenic acid content in triazole-exposed plants may promote resistance to abiotic stress.

Medium-chain-length polyprenol (C45-C55) formation in chloroplasts of Arabidopsis is brassinosteroid-dependent

Brassinosteroids are important plant hormones influencing, among other processes, chloroplast development, the electron transport chain during light reactions of photosynthesis, and the Calvin-Benson cycle. Medium-chain-length polyprenols built of 9-11 isoprenoid units (C45-C55 carbons) are a class of isoprenoid compounds present in abundance in thylakoid membranes. They are synthetized in chloroplast by CPT7 gene from Calvin cycle derived precursors on MEP (methylerythritol 4-phosphate) isoprenoid biosynthesis pathway. C45-C55 polyprenols affect thylakoid membrane ultra-structure and hence influence photosynthetic apparatus performance in plants such as Arabidopsis and tomato. So far nothing is known about the hormonal or environmental regulation of CPT7 gene expression. The aim of our study was to find out if medium-chain-length polyprenol biosynthesis in plants may be regulated by hormonal cues.We found that the CPT7 gene in Arabidopsis has a BZR1 binding element (brassinosteroid dependent) in its promoter. Brassinosteroid signaling mutants in Arabidopsis accumulate a lower amount of medium-chain-length C45-C55 polyprenols than control plants. At the same time carotenoid and chlorophyll content is increased, and the amount of PsbD1A protein coming from photosystem II does not undergo a significant change. On contrary, treatment of WT plants with epi-brassinolide increases C45-C55 polyprenols content. We also report decreased transcription of MEP enzymes (besides C45-C55 polyprenols, precursors of numerous isoprenoids, e.g. phytol, carotenoids are derived from this pathway) and genes encoding biosynthesis of medium-chain-length polyprenol enzymes in brassinosteroid perception mutant bri1-116. Taken together, we document that brassinosteroids affect biosynthetic pathway of C45-C55 polyprenols.

Biosynthetic Pathways of Hormones in Plants

Phytohormones exhibit a wide range of chemical structures, though they primarily originate from three key metabolic precursors: amino acids, isoprenoids, and lipids. Specific amino acids, such as tryptophan, methionine, phenylalanine, and arginine, contribute to the production of various phytohormones, including auxins, melatonin, ethylene, salicylic acid, and polyamines. Isoprenoids are the foundation of five phytohormone categories: cytokinins, brassinosteroids, gibberellins, abscisic acid, and strigolactones. Furthermore, lipids, i.e., α-linolenic acid, function as a precursor for jasmonic acid. The biosynthesis routes of these different plant hormones are intricately complex. Understanding of these processes can greatly enhance our knowledge of how these hormones regulate plant growth, development, and physiology. This review focuses on detailing the biosynthetic pathways of phytohormones.

Feedback Inhibition Might Dominate the Accumulation Pattern of BR in the New Shoots of Tea Plants (Camellia sinensis)

Brassinosteroid (BR), a kind of polyhydroxylated steroid hormone, plays an important role in physiological and biochemical processes in plants. Studies were mainly focused on BR signaling and its exogenous spraying to help enhance crop yields. Few research studies are centered on the accumulation pattern of BR and its mechanism. Yet, it is crucial to unlock the mystery of the function of BR and its cross action with other hormones. Tea (Camellia sinensis (L.) O. Kuntze) is one of the important economic crops in some countries, and new shoots are the raw materials for the preparation of various tea products. Different concentrations of exogenous BR were reported to have different effects on growth and development. New shoots of tea plants can thus be considered a valuable research object to study the accumulation pattern of BR. In this study, the quantity of five BR components (brassinolide, 28-norbrassinolide, 28-homobrassinolide, castasterone, and 28-norcastasterone) in different tissues of tea plants, including buds (Bud), different maturity of leaves (L1, L2), and stems (S1, S2) were determined by UPLC-MS/MS. A total of 15 cDNA libraries of the same tissue with three repetitions for each were constructed and sequenced. The BR-accumulation pattern and gene expression pattern were combined together for weighted gene co-expression network analysis (WGCNA). BR-accumulation-relative genes were then screened using two methods, based on the K.in value and BR biosynthetic pathway (ko00905), respectively. The result showed that photosynthesis-related genes and CYP450 family genes were actively involved and might play important roles in BR accumulation and/or its accumulation pattern. First and foremost, feedback inhibition was more likely to dominate the accumulation pattern of BR in the new shoots of tea plants. Moreover, three conserved miRNAs with their target transcriptional factors and target mRNAs had been figured out from negative correlation modules that might be strongly linked to the BR-accumulation pattern. Our study provided an experimental basis for the role of BR in tea plants. The excavation of genes related to the accumulation pattern of BR provided the possibility of cross-action studies on the regulation of BR biosynthesis and the study between BR and other hormones.

Brassinosteroids (BRs) Role in Plant Development and Coping with Different Stresses

Plants are vulnerable to a number of abiotic and biotic stresses that cause a substantial decrease in the production of plants. Plants respond to different environmental stresses by experiencing a series of molecular and physiological changes coordinated by various phytohormones. The use of phytohormones to alleviate stresses has recently achieved increasing interest. Brassinosteroids (BRs) are a group of polyhydroxylated steroidal phytohormones that are required for the development, growth, and productivity of plants. These hormones are involved in regulating the division, elongation, and differentiation of numerous cell types throughout the entire plant life cycle. BR studies have drawn the interest of plant scientists over the last few decades due to their flexible ability to mitigate different environmental stresses. BRs have been shown in numerous studies to have a positive impact on plant responses to various biotic and abiotic stresses. BR receptors detect the BR at the cell surface, triggering a series of phosphorylation events that activate the central transcription factor (TF) Brassinazole-resistant 1 (BZR1), which regulates the transcription of BR-responsive genes in the nucleus. This review discusses the discovery, occurrence, and chemical structure of BRs in plants. Furthermore, their role in the growth and development of plants, and against various stresses, is discussed. Finally, BR signaling in plants is discussed.

Brassinosteroids Benefit Plants Performance by Augmenting Arbuscular Mycorrhizal Symbiosis

Arbuscular mycorrhizal (AM) play an important role in improving plant growth and development. The interaction between phytohormones and AM symbiosis is gradually revealed. Here we examined the effect of Brassinosteroids (BR) on AM symbiosis and discussed the synergistic promotion of plant growth by BR and AM symbiosis. The xylophyta Eucalyptus grandis Hill (E. grandis) was inoculated with AM fungi Rhizoglomus irregularis R197198 (R. irregularis) and treated with different concentrations (0, 1, 10, and 100 nM) of 24-epibrassinolide (24-epiBL) for 6 weeks. With the increase of 24-epiBL concentration, E. grandis growth was firstly promoted and then inhibited, but inoculation with AM fungi alleviated this inhibition. 24-epiBL and R. irregularis colonization significantly improved E. grandis growth and antioxidant system response, and the synergistic effect was the best. Compared with the control group, 24-epiBL treatment significantly increased the mycorrhizal colonization and arbuscular abundance of AM fungi R. irregular in E. grandis roots. The expression of AM symbiosis maker genes was significantly increased by 24-epiBL treatment. Both 24-epiBL treatment and AM colonization upregulated gibberellins (GA) synthesis genes, but no inhibition caused by GA levels was found. 24-epiBL is a kind of synthetic highly active BR. Based on the results of 24-epiBL treatment, we hypothesized that BR actively regulates AM symbiosis regulates AM symbiosis without affecting GA-INSENSITIVE DWARF1 (GID1)-DELLA expression. The synergistic treatment of BR and AM symbiosis can significantly promote the growth and development of plants. IMPORTANCE Brassinosteroids (BR) and Arbuscular mycorrhizas (AM) symbiosis play an important role in improving plant growth and development. Previous studies have shown that there is a complex regulatory network between phytohormones and AM symbiosis. However, the interactions of BR-signaling and AM symbiosis are still poorly understood. Our results suggest that BR actively regulates the colonization and development of AM fungi, and AM fungal colonization can alleviate the inhibition of plant growth caused by excessive BR. In addition, BR actively regulates AM symbiosis, but does not primarily mediate gibberellins-DELLA interaction. The synergistic treatment of BR and AM symbiosis can significantly promote the growth and development of plants. The conclusions of this study provide a reference for phytohormones-AM symbiosis interaction.

Emerging roles of brassinosteroids and light in anthocyanin biosynthesis and ripeness of climacteric and non-climacteric fruits

Anthocyanins are important pigments that contribute to fruit quality. The regulation of anthocyanin biosynthesis by several transcription factors via sophisticated regulatory networks has been studied in various plants. Brassinosteroids (BRs), a new class of plant hormone, are involved in regulating anthocyanin biosynthesis in fruits. Furthermore, light directly affects the synthesis and distribution of anthocyanins. Here, we summarize the recent progress toward understanding the impact of BR and light on anthocyanin biosynthesis in climacteric and non-climacteric fruits. We review the BR and light signaling pathways and highlight the important transcription factors that are associated with the synthesis of anthocyanins, such as BZR1 (brassinazole-resistant 1, BR signaling pathway), HY5 (elongated hypocotyl 5) and COP1 (constitutively photomorphogenic 1, light signal transduction pathway), which bind with the target genes involved in anthocyanin synthesis. In addition, we review the mechanism by which light signals interact with hormonal signals to regulate anthocyanin biosynthesis.

Vineyard environments influence Malbec grapevine phenotypic traits and DNA methylation patterns in a clone-dependent way

By studying three cv. Malbec clones cultivated in two vineyards with contrasting environmental conditions, we demonstrated that DNA methylation has an important role in the phenotypic plasticity and that epigenetic modulation is clone-dependent. Clonal selection and vegetative propagation determine low genetic variability in grapevine cultivars, although it is common to observe diverse phenotypes. Environmental signals may induce epigenetic changes altering gene expression and phenotype. The range of phenotypes that a genotype expresses in different environments is known as phenotypic plasticity. DNA methylation is the most studied epigenetic mechanism, but only few works evaluated this novel source of variability in grapevines. In the present study, we analyzed the effects on phenotypic traits and epigenome of three Vitis vinifera cv. Malbec clones cultivated in two contrasting vineyards of Mendoza, Argentina. Anonymous genome regions were analyzed using methylation-sensitive amplified polymorphism (MSAP) markers. Clone-dependent phenotypic and epigenetic variability between vineyards were found. The clone that presented the clearer MSAP differentiation between vineyards was selected and analyzed through reduced representation bisulfite sequencing. Twenty-nine differentially methylated regions between vineyards were identified and associated to genes and/or promoters. We discuss about a group of genes related to hormones homeostasis and sensing that could provide a hint of the epigenetic role in the determination of the different phenotypes observed between vineyards and conclude that DNA methylation has an important role in the phenotypic plasticity and that epigenetic modulation is clone-dependent.

A critical evaluation of some of the recent so-called 'evidence' for the involvement of vertebrate-type sex steroids in the reproduction of mollusks

Many studies on the control of reproduction in mollusks have focused on hormones (and proteins associated with the production and signaling of those hormones) which were originally discovered in humans, in the belief that if they are also present in mollusks, they must have the same role. However, although human sex steroids can be found in mollusks, they are so readily absorbed that their presence is not necessarily evidence of endogenous synthesis. A homolog of the vertebrate nuclear estrogen receptor has been found in mollusks, but it does not bind to estrogens or indeed to any steroid at all. Antibodies against human aromatase show positive immunostaining in mollusks, yet the aromatase gene has not been found in the genome of any invertebrates (let alone mollusks). This review will deal with these and other examples of contradictory evidence for a role of human hormones in invertebrate reproduction.

Establishment of Biosynthetic Pathways To Generate Castasterone as the Biologically Active Brassinosteroid in Brachypodium distachyon

Gas chromatography-mass spectrometry (GC-MS) analysis revealed that castasterone and its biosynthetic precursors are found in Brachypodium distachyon. In vitro conversion experiments with crude enzyme solutions prepared from B. distachyon demonstrated the presence of the following biosynthetic sequences: campesterol → campesta-4-en-3-one → campesta-3-one → campestanol → 6-deoxocathasterone → 6-deoxoteasterone → teasterone ↔ 3-dehydroteasterone ↔ typhasterol → castasterone. campesterol → 22-hydroxycampesterol → 22-hydroxy-campesta-4-en-3-one → 22-hydroxy-campesta-3-one → 6-deoxo-3-dehydroteasterone → 3-dehydroteasterone. 6-deoxoteasterone ↔ 6-deoxo-3-dehydroteasterone ↔ 6-deoxotyphasterol → 6-deoxocastasterone → castasterone. This shows that there are campestanol-dependent and campestanol-independent pathway in B. distachyon that synthesize 24-methylated brassinosteroids (BRs). Biochemical analysis of BRs biosynthetic enzymes confirmed that BdDET2, BdCYP90B1, BdCYP90A1, BdCYP90D2, and BdCYP85A1 are orthologous to BR 5α-reductase, BR C-22 hydroxylase, BR C-3 oxidase, BR C-23 hydroxylase, and BR C-6 oxidase, respectively. Brassinolide was not identified in B. distachyon. Additionally, B. distachyon crude enzyme solutions could not catalyze the conversion of castasterone to brassinolide, and the gene encoding an ortholog of CYP85A2 (a brassinolide synthase) was not found in B. distachyon. These results strongly suggest that the end product for brassinosteroid biosynthesis which controls the growth and development of B. distachyon is not brassinolide but rather castasterone.

Comprehensive Overview of the Brassinosteroid Biosynthesis Pathways: Substrates, Products, Inhibitors, and Connections

Brassinosteroids (BRs) as a class of steroid plant hormones participate in the regulation of numerous developmental processes, including root and shoot growth, vascular differentiation, fertility, flowering, and seed germination, as well as in responding to environmental stresses. During four decades of research, the BR biosynthetic pathways have been well studied with forward- and reverse genetics approaches. The free BRs contain 27, 28, and 29 carbons within their skeletal structure: (1): 5α-cholestane or 26-nor-24α-methyl-5α-cholestane for C₂₇-BRs; (2) 24α-methyl-5α-cholestane, 24β-methyl-5α-cholestane or 24-methylene-5α-cholestane for C₂₈-BRs; (3) 24α-ethyl-5α-cholestane, 24(Z)-ethylidene-5α-cholestane, 25-methyl-5α-campestane or 24-methylene-25-methyl-5α-cholestane for C₂₉-BRs, as well as different kinds and orientations of oxygenated functions in A- and B-ring. These alkyl substituents are also common structural features of sterols. BRs are derived from sterols carrying the same side chain. The C₂₇-BRs without substituent at C-24 are biosynthesized from cholesterol. The C₂₈-BRs carrying either an α-methyl, β-methyl, or methylene group are derived from campesterol, 24-epicampesterol or 24-methylenecholesterol, respectively. The C₂₉-BRs with an α-ethyl group are produced from sitosterol. Furthermore, the C₂₉ BRs carrying methylene at C-24 and an additional methyl group at C-25 are derived from 24-methylene-25-methylcholesterol. Generally, BRs are biosynthesized via cycloartenol and cycloartanol dependent pathways. Till now, more than 17 compounds were characterized as inhibitors of the BR biosynthesis. For nine of the inhibitors (e.g., brassinazole and YCZ-18) a specific target reaction within the BR biosynthetic pathway has been identified. Therefore, the review highlights comprehensively recent advances in our understanding of the BR biosynthesis, sterol precursors, and dependencies between the C₂₇-C₂₈ and C₂₈-C₂₉ pathways.