Proteomic study identifies proteins involved in brassinosteroid regulation of rice growth

The Glycine-Rich RNA-Binding Protein Is a Vital Post-Transcriptional Regulator in Crops

Glycine-rich RNA binding proteins (GR-RBPs), a branch of RNA binding proteins (RBPs), play integral roles in regulating various aspects of RNA metabolism regulation, such as RNA processing, transport, localization, translation, and stability, and ultimately regulate gene expression and cell fate. However, our current understanding of GR-RBPs has predominantly been centered on Arabidopsis thaliana, a model plant for investigating plant growth and development. Nonetheless, an increasing body of literature has emerged in recent years, shedding light on the presence and functions of GRPs in diverse crop species. In this review, we not only delineate the distinctive structural domains of plant GR-RBPs but also elucidate several contemporary mechanisms of GR-RBPs in the post-transcriptional regulation of RNA. These mechanisms encompass intricate processes, including RNA alternative splicing, polyadenylation, miRNA biogenesis, phase separation, and RNA translation. Furthermore, we offer an exhaustive synthesis of the diverse roles that GR-RBPs fulfill within crop plants. Our overarching objective is to provide researchers and practitioners in the field of agricultural genetics with valuable insights that may inform and guide the application of plant genetic engineering for enhanced crop development and sustainable agriculture.

Fine-tuning brassinosteroid biosynthesis via 3'UTR-dependent decay of CPD mRNA modulates wood formation in Populus

Brassinosteroids (BRs) are plant hormones that regulate wood formation in trees. Currently, little is known about the post-transcriptional regulation of BR synthesis. Here, we show that during wood formation, fine-tuning BR synthesis requires 3'UTR-dependent decay of Populus CONSTITUTIVE PHOTOMORPHOGENIC DWARF 1 (PdCPD1). Overexpression of PdCPD1 or its 3' UTR fragment resulted in a significant increase of BR levels and inhibited secondary growth. In contrast, transgenic poplars repressing PdCPD1 3' UTR expression displayed moderate levels of BR and promoted wood formation. We show that the Populus GLYCINE-RICH RNA-BINDING PROTEIN 1 (PdGRP1) directly binds to a GU-rich element in 3' UTR of PdCPD1, leading to its mRNA decay. We thus provide a post-transcriptional mechanism underlying BRs synthesis during wood formation, which may be useful for genetic manipulation of wood biomass in trees.

Relationship between the Phenylpropanoid Pathway and Dwarfism of Paspalum seashore Based on RNA-Seq and iTRAQ

Seashore paspalum is a major warm-season turfgrass requiring frequent mowing. The use of dwarf cultivars with slow growth is a promising method to decrease mowing frequency. The present study was conducted to provide an in-depth understanding of the molecular mechanism of T51 dwarfing in the phenylpropane pathway and to screen the key genes related to dwarfing. For this purpose, we obtained transcriptomic information based on RNA-Seq and proteomic information based on iTRAQ for the dwarf mutant T51 of seashore paspalum. The combined results of transcriptomic and proteomic analysis were used to identify the differential expression pattern of genes at the translational and transcriptional levels. A total of 8311 DEGs were detected at the transcription level, of which 2540 were upregulated and 5771 were downregulated. Based on the transcripts, 2910 proteins were identified using iTRAQ, of which 392 (155 upregulated and 237 downregulated) were DEPs. The phenylpropane pathway was found to be significantly enriched at both the transcriptional and translational levels. Combined with the decrease in lignin content and the increase in flavonoid content in T51, we found that the dwarf phenotype of T51 is closely related to the abnormal synthesis of lignin and flavonoids in the phenylpropane pathway. CCR and HCT may be the key genes for T51 dwarf. This study provides the basis for further study on the dwarfing mechanism of seashore paspalum. The screening of key genes lays a foundation for further studies on the molecular mechanism of seashore paspalum dwarfing.

Modification of Threonine-825 of SlBRI1 Enlarges Cell Size to Enhance Fruit Yield by Regulating the Cooperation of BR-GA Signaling in Tomato

Brassinosteroids (BRs) are growth-promoting phytohormones that can efficiently function by exogenous application at micromolar concentrations or by endogenous fine-tuning of BR-related gene expression, thus, precisely controlling BR signal strength is a key factor in exploring the agricultural potential of BRs. BRASSINOSTEROID INSENSITIVE1 (BRI1), a BR receptor, is the rate-limiting enzyme in BR signal transduction, and the phosphorylation of each phosphorylation site of SlBRI1 has a distinct effect on BR signal strength and botanic characteristics. We recently demonstrated that modifying the phosphorylation sites of tomato SlBRI1 could improve the agronomic traits of tomato to different extents; however, the associated agronomic potential of SlBRI1 phosphorylation sites in tomato has not been fully exploited. In this research, the biological functions of the phosphorylation site threonine-825 (Thr-825) of SlBRI1 in tomato were investigated. Phenotypic analysis showed that, compared with a tomato line harboring SlBRI1, transgenic tomato lines expressing SlBRI1 with a nonphosphorylated Thr-825 (T825A) exhibited a larger plant size due to a larger cell size and higher yield, including a greater plant height, thicker stems, longer internodal lengths, greater plant expansion, a heavier fruit weight, and larger fruits. Molecular analyses further indicated that the autophosphorylation level of SlBRI1, BR signaling, and gibberellic acid (GA) signaling were elevated when SlBRI1 was dephosphorylated at Thr-825. Taken together, the results demonstrated that dephosphorylation of Thr-825 can enhance the functions of SlBRI1 in BR signaling, which subsequently activates and cooperates with GA signaling to stimulate cell elongation and then leads to larger plants and higher yields per plant. These results also highlight the agricultural potential of SlBRI1 phosphorylation sites for breeding high-yielding tomato varieties through precise control of BR signaling.

Roles of Plant Glycine-Rich RNA-Binding Proteins in Development and Stress Responses

In recent years, much progress has been made in elucidating the functional roles of plant glycine-rich RNA-binding proteins (GR-RBPs) during development and stress responses. Canonical GR-RBPs contain an RNA recognition motif (RRM) or a cold-shock domain (CSD) at the N-terminus and a glycine-rich domain at the C-terminus, which have been associated with several different RNA processes, such as alternative splicing, mRNA export and RNA editing. However, many aspects of GR-RBP function, the targeting of their RNAs, interacting proteins and the consequences of the RNA target process are not well understood. Here, we discuss recent findings in the field, newly defined roles for GR-RBPs and the actions of GR-RBPs on target RNA metabolism.

24-epibrassinolide-induced growth promotion of wheat seedlings is associated with changes in the proteome and tyrosine phosphoproteome

Brassinosteroids (BRs) represent a unique class of steroidal plant hormones that display pronounced growth-promoting activity at very low concentrations. Although many efforts have been made to characterize the molecular basis of BR action, little is known about the mechanisms behind the growth-promoting effect of BRs at protein level. Proteomic analysis of response to the steroid plant hormone 24-epibrassinolide (EBR) in wheat seedling shoots (Triticum aestivum L.) was performed using two-dimensional electrophoresis (2-DE) and immunoblotting with highly specific antibodies (PY20) to phosphotyrosine. EBR-modulated proteins and phosphotyrosine polypeptides were identified using MALDI-TOF mass spectrometry. The study revealed that EBR-stimulated growth of wheat seedlings was accompanied by changes in the content of multiple proteins as well as in tyrosine phosphorylation of numerous polypeptides. Among them, 22 differentially accumulated proteins and 13 phosphotyrosine proteins were identified. Based on their performed functions, the identified proteins are involved in physiological processes (photosynthesis, growth, energy and amino acid metabolism) closely associated with intensification of plant metabolism. The EBR-induced changes in protein abundance and tyrosine phosphorylation profile may contribute to growth stimulation of wheat seedlings under the action of EBR. The obtained data suggest an important role for EBR in the activation of protein metabolism underlying fundamental physiological processes, including growth promotion.

The mitochondrial isoform glutathione peroxidase 3 (OsGPX3) is involved in ABA responses in rice plants

Different environmental conditions can lead plants to a condition termed oxidative stress, which is characterized by a disruption in the equilibrium between the production of reactive oxygen species (ROS) and antioxidant defenses. Glutathione peroxidase (GPX), an enzyme that acts as a peroxide scavenger in different organisms, has been identified as an important component in the signaling pathway during the developmental process and in stress responses in plants and yeast. Here, we demonstrate that the mitochondrial isoform of rice (Oryza sativa L. ssp. Japonica cv. Nipponbare) OsGPX3 is induced after treatment with the phytohormone abscisic acid (ABA) and is involved in its responses and in epigenetic modifications. Plants that have been silenced for OsGPX3 (gpx3i) present substantial changes in the accumulation of proteins related to these processes. These plants also have several altered ABA responses, such as germination, ROS accumulation, stomatal closure, and dark-induced senescence. This study is the first to demonstrate that OsGPX3 plays a role in ABA signaling and corroborate that redox homeostasis enzymes can act in different and complex pathways in plant cells. SIGNIFICANCE: This work proposes the mitochondrial glutathione peroxidase (OsGPX3) as a novel ABA regulatory pathway component. Our results suggest that this antioxidant enzyme is involved in ABA-responses, highlighting the complex pathways that these proteins can participate beyond the regulation of cellular redox status.

Dissection of brassinosteroid-regulated proteins in rice embryos during germination by quantitative proteomics

Brassinosteroids (BRs), essential plant-specific steroidal hormones, function in a wide spectrum of plant growth and development events, including seed germination. Rice is not only a monocotyledonous model plant but also one of the most important staple food crops of human beings. Rice seed germination is a decisive event for the next-generation of plant growth and successful seed germination is critical for rice yield. However, little is known about the molecular mechanisms on how BR modulates seed germination in rice. In the present study, we used isobaric tags for relative and absolute quantification (iTRAQ) based proteomic approach to study BR-regulated proteome during the early stage of seed germination. The results showed that more than 800 BR-responsive proteins were identified, including 88 reliable target proteins responsive to stimuli of both BR-deficiency and BR-insensitivity. Moreover, 90% of the 88 target proteins shared a similar expression change pattern. Gene ontology and string analysis indicated that ribosomal structural proteins, as well as proteins involved in protein biosynthesis and carbohydrate metabolisms were highly clustered. These findings not only enrich BR-regulated protein database in rice seeds, but also allow us to gain novel insights into the molecular mechanism of BR regulated seed germination.

A phloem-limited fijivirus induces the formation of neoplastic phloem tissues that house virus multiplication in the host plant

A number of phloem-limited viruses induce the development of tumours (enations) in the veins of host plants, but the relevance of tumour induction to the life cycle of those viruses is unclear. In this study, we performed molecular and structural analyses of tumours induced by rice black-streaked dwarf virus (RBSDV, genus Fijivirus) infection in maize plants. The transcript level of the maize cdc2 gene, which regulates the cell cycle, was highly elevated in tumour tissues. Two-dimensional electrophoresis identified 25 cellular proteins with altered accumulation in the tumour tissues. These proteins are involved in various metabolic pathways, including photosynthesis, redox, energy pathways and amino acid synthesis. Histological analysis indicated that the tumours predominantly originated from hyperplastic growth of phloem, but those neoplastic tissues have irregular structures and cell arrangements. Immunodetection assays and electron microscopy observations indicated that in the shoots, RBSDV is confined to phloem and tumour regions and that virus multiplication actively occurs in the tumour tissue, as indicated by the high accumulation of non-structural proteins and formation of viroplasms in the tumour cells. Thus, the induction of tumours by RBSDV infection provides a larger environment that is favourable for virus propagation in the host plant.

Gene expression and functional analyses in brassinosteroid-mediated stress tolerance

The plant hormone brassinosteroid (BR) plays essential roles in plant growth and development, while also controlling plant stress responses. This dual ability of BR is intriguing from a mechanistic point of view and as a viable solution for stabilizing crop yields under the changing climatic conditions. Here we report a time course analysis of BR responses under both stress and no-stress conditions, the results of which establish that BR incorporates many stress-related features even under no-stress conditions, which are then accompanied by a dynamic stress response under unfavourable conditions. Found within the BR transcriptome were distinct molecular signatures of two stress hormones, abscisic acid and jasmonic acid, which were correlated with enhanced endogenous levels of the two hormones in BR-treated seedlings. The marked presence of genes related to protein metabolism and modification, defence responses and calcium signalling highlights the significance of their associated mechanisms and roles in BR processes. Functional analysis of loss-of-function mutants of a subset of genes selected from the BR transcriptome identified abiotic stress-related roles for ACID PHOSPHATASE5 (ACP5), WRKY33, JACALIN-RELATED LECTIN1-3 (JAC-LEC1-3) and a BR-RESPONSIVE-RECEPTOR-LIKE KINASE (BRRLK). Overall, the results of this study provide a clear link between the molecular changes impacted by BR and its ability to confer broad-range stress tolerance, emphasize the importance of post-translational modification and protein turnover as BR regulatory mechanisms and demonstrate the BR transcriptome as a repertoire of new stress-related regulatory and structural genes.

Role of the proteome in phytohormonal signaling

Phytohormones are orchestrators of plant growth and development. A lot of time and effort has been invested in attempting to comprehend their complex signaling pathways but despite success in elucidating some key components, molecular mechanisms in the transduction pathways are far from being resolved. The last decade has seen a boom in the analysis of phytohormone-responsive proteins. Abscisic acid, auxin, brassinosteroids, cytokinin, ethylene, gibberellins, nitric oxide, oxylipins, strigolactones, salicylic acid--all have been analyzed to various degrees. For this review, we collected data from proteome-wide analyses resulting in a list of over 2000 annotated proteins from Arabidopsis proteomics and nearly 500 manually filtered protein families merged from all the data available from different species. We present the currently accepted model of phytohormone signaling, highlight the contributions made by proteomic-based research and describe the key nodes in phytohormone signaling networks, as revealed by proteome analysis. These include ubiquitination and proteasome mediated degradation, calcium ion signaling, redox homeostasis, and phosphoproteome dynamics. Finally, we discuss potential pitfalls and future perspectives in the field. This article is part of a Special Issue entitled: Plant Proteomics--a bridge between fundamental processes and crop production, edited by Dr. Hans-Peter Mock.

Transcriptomic analysis of rice in response to iron deficiency and excess

BACKGROUND

Iron (Fe) is essential micronutrient for plants and its deficiency as well as toxicity is a serious agricultural problem. The mechanisms of Fe deficiency are reasonably understood, however our knowledge about plants response to excess Fe is limited. Moreover, the regulation of small open reading frames (sORFs) in response to abiotic stress has not been reported in rice. Understanding the regulation of rice transcriptome in response to Fe deficiency and excess could provide bases for developing strategies to breed plants tolerant to Fe deficiency as well as excess Fe.

RESULTS

We used a novel rice 110 K microarray harbouring ~48,620 sORFs to understand the transcriptomic changes that occur in response to Fe deficiency and excess. In roots, 36 genes were upregulated by excess Fe, of which three were sORFs. In contrast, 1509 genes were upregulated by Fe deficiency, of which 90 (6%) were sORFs. Co-expression analysis revealed that the expression of some sORFs was positively correlated with the genes upregulated by Fe deficiency. In shoots, 50 (19%) of the genes upregulated by Fe deficiency and 1076 out of 2480 (43%) genes upregulated by excess Fe were sORFs. These results suggest that excess Fe may significantly alter metabolism, particularly in shoots.

CONCLUSION

These data not only reveal the genes regulated by excess Fe, but also suggest that sORFs might play an important role in the response of plants to Fe deficiency and excess.

Transcriptome and proteome profiling of adventitious root development in hybrid larch (Larix kaempferi × Larix olgensis)

BACKGROUND

Hybrids of larch (Larix kaempferi × Larix olgensis) are important afforestation species in northeastern China. They are routinely propagated via rooted stem cuttings. Despite the importance of rooting, little is known about the regulation of adventitious root development in larch hybrids. 454 GS FLX Titanium technology represents a new method for characterizing the transcriptomes of non-model species. This method can be used to identify differentially expressed genes, and then two-dimensional difference gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF/TOF MS) analyses can be used to analyze their corresponding proteins. In this study, we analyzed semi-lignified cuttings of two clones of L. kaempferi × L. olgensis with different rooting capacities to study the molecular basis of adventitious root development.

RESULTS

We analyzed two clones; clone 25-5, with strong rooting capacity, and clone 23-12, with weak rooting capacity. We constructed four cDNA libraries from 25-5 and 23-12 at two development stages. Sequencing was conducted using the 454 pyrosequencing platform. A total of 957832 raw reads was produced; 95.07% were high-quality reads, and were assembled into 45137 contigs and 61647 singletons. The functions of the unigenes, as indicated by their Gene Ontology annotation, included diverse roles in the molecular functions, biological processes, and cellular component categories. We analyzed 75 protein spots (-fold change ≥ 2, P ≤ 0.05) by 2D-DIGE, and identified the differentially expressed proteins using MALDI-TOF/TOF MS. A joint analysis of transcriptome and proteome showed genes related to two pathways, polyamine synthesis and stress response, might play an important role on adventitious root development.

CONCLUSIONS

These results provide fundamental and important information for research on the molecular mechanism of adventitious root development. We also demonstrated for the first time the combined use of two important technologies as a powerful approach to advance research on non-model, but otherwise important, larch species.

Rice proteomics: a model system for crop improvement and food security

Rice proteomics has progressed at a tremendous pace since the year 2000, and that has resulted in establishing and understanding the proteomes of tissues, organs, and organelles under both normal and abnormal (adverse) environmental conditions. Established proteomes have also helped in re-annotating the rice genome and revealing the new role of previously known proteins. The progress of rice proteomics had recognized it as the corner/stepping stone for at least cereal crops. Rice proteomics remains a model system for crops as per its exemplary proteomics research. Proteomics-based discoveries in rice are likely to be translated in improving crop plants and vice versa against ever-changing environmental factors. This review comprehensively covers rice proteomics studies from August 2010 to July 2013, with major focus on rice responses to diverse abiotic (drought, salt, oxidative, temperature, nutrient, hormone, metal ions, UV radiation, and ozone) as well as various biotic stresses, especially rice-pathogen interactions. The differentially regulated proteins in response to various abiotic stresses in different tissues have also been summarized, indicating key metabolic and regulatory pathways. We envision a significant role of rice proteomics in addressing the global ground level problem of food security, to meet the demands of the human population which is expected to reach six to nine billion by 2040.

Brassinosteroid signaling network: implications on yield and stress tolerance

The steroidal hormone brassinosteroids (BRs) play important roles in plant growth and development. Genetic, genomic and proteomic studies in Arabidopsis have identified major BR signaling components and elucidated the signal transduction pathway from the cell surface receptor kinase BRI1 to the BES1/BZR1 family of transcription factors. BRs interact with other plant hormones in coordinating gene expression and plant growth and development. In this review, we provide an update on the latest progress in characterizing the BR signaling network and discuss its interactions with other hormone pathways in determining yield component traits and in regulating stress responses.

The Bsister MADS gene FST determines ovule patterning and development of the zygotic embryo and endosperm

Many homeotic MADS-box genes have been identified as controllers of the floral transition and floral development. However, information regarding B_sister (B_s)-function genes in monocots is still limited. Here, we describe the functional characterization of a B_s-group MADS-box gene FEMALE-STERILE (FST), whose frame-shift mutation (fst) results in abnormal ovules and the complete abortion of zygotic embryos and endosperms in rice. Anatomical analysis showed that the defective development in the fst mutant exclusively occurred in sporophytic tissues including integuments, fertilized proembryos and endosperms. Analyses of the spatio-temporal expression pattern revealed that the prominent FST gene products accumulated in the inner integument, nucellar cell of the micropylar side, apical and base of the proembryos and free endosperm nuclei. Microarray and gene ontology analysis unraveled substantial changes in the expression level of many genes in the fst mutant ovules and seeds, with a subset of genes involved in several developmental and hormonal pathways appearing to be down-regulated. Using both forward and reverse genetics approaches, we demonstrated that rice FST plays indispensable roles and multiple functions during ovule and early seed development. These findings support a novel function for the B_s-group MADS-box genes in plants.

Brassinosteroid signaling network and regulation of photomorphogenesis

In plants, the steroidal hormone brassinosteroid (BR) regulates numerous developmental processes, including photomorphogenesis. Genetic, proteomic, and genomic studies in Arabidopsis have illustrated a fully connected BR signal transduction pathway from the cell surface receptor kinase BRI1 to the BZR1 family of transcription factors. Genome-wide analyses of protein-DNA interactions have identified thousands of BZR1 target genes that link BR signaling to various cellular, metabolic, and developmental processes, as well as other signaling pathways. In controlling photomorphogenesis, BR signaling is highly integrated with the light, gibberellin, and auxin pathways through both direct interactions between signaling proteins and transcriptional regulation of key components of these pathways. BR signaling also cross talks with other receptor kinase pathways to modulate stomata development and innate immunity. The molecular connections in the BR signaling network demonstrate a robust steroid signaling system that has evolved in plants to orchestrate signal transduction, genome expression, metabolism, defense, and development.

Brassinosteroid action in flowering plants: a Darwinian perspective

The year 2012 marks the 150th anniversary of the publication of Charles Darwin's first botanical book, on the fertilization of orchids (1862), wherein he described pollen grains and outlined his evolutionary principles with respect to plant research. Five decades later, the growth-promoting effect of extracts of Orchid pollen on coleoptile elongation was documented. These studies led to the discovery of a new class of phytohormones, the brassinosteroids (BRs) that were isolated from rapeseed (Brassica napus) pollen. These growth-promoting steroids, which regulate height, fertility, and seed-filling in crop plants such as rice (Oryza sativa), also induce stress- and disease resistance in green algae and angiosperms. The origin and current status of BR-research is described here, with reference to BR-action and -signal transduction, and it is shown that modern high-yield rice varieties with erect leaves are deficient in endogenous BRs. Since brassinosteroids induce pathogen resistance in rice plants and hence can suppress rice blast- and bacterial blight-diseases, genetic manipulation of BR-biosynthesis or -perception may be a means to increase crop production. Basic research on BR activity in plants, such as Arabidopsis and rice, has the potential to increase crop yields further as part of a 21th century 'green biotech-revolution' that can be traced back to Darwin's classical breeding experiments. It is concluded that 'Nothing in brassinosteroid research makes sense except in the light of Darwinian evolution' and the value of basic science is highlighted, with reference to the genetic engineering of better food crops that may become resistant to a variety of plant diseases.

Brassinosteroid enhances jasmonate-induced anthocyanin accumulation in Arabidopsis seedlings

Jasmonate (JA) regulates plant development, mediates defense responses, and induces anthocyanin biosynthesis as well. Previously, we isolated the psc1 mutant that partially suppressed coi1 insensitivity to JA, and found that brassinosteroid (BR) was involved in JA signaling and negatively regulated JA inhibition of root growth in Arabidopsis. In this study it was shown that JA-induced anthocyanin accumulation was reduced in BR mutants or in wild type treated with brassinazole, an inhibitor of BR biosynthesis, whereas it was induced by an application of exogenous BR. It was also shown that the 'late' anthocyanin biosynthesis genes including DFR, LDOX, and UF3GT, were induced slightly by JA in the BR mutants relative to wild type. Furthermore, the expression level of JA-induced Myb/bHLH transcription factors such as PAP1, PAP2, and GL3, which are components of the WD-repeat/Myb/bHLH transcriptional complexes that mediate the 'late' anthocyanin biosynthesis genes, was lower in the BR mutants than that in wild type. These results suggested that BR affects JA-induced anthocyanin accumulation by regulating the 'late' anthocyanin biosynthesis genes and this regulation might be mediated by the WD-repeat/Myb/bHLH transcriptional complexes.

Recent advances in the regulation of brassinosteroid signaling and biosynthesis pathways

Brassinosteroids (BRs) play important roles in plant growth, development and responses to environmental cues. BRs signal through plasma membrane receptor BRI1 and co-receptor BAK1, and several positive (BSK1, BSU1, PP2A) and negative (BKI1, BIN2 and 14-3-3) regulators to control the activities of BES1 and BZR1 family transcription factors, which regulate the expression of hundreds to thousands of genes for various BR responses. Recent studies identified novel signaling components in the BR pathways and started to establish the detailed mechanisms on the regulation of BR signaling. In addition, the molecular mechanism and transcriptional network through which BES1 and BZR1 control gene expression and various BR responses are beginning to be revealed. BES1 recruits histone demethylases ELF6 and REF6 as well as a transcription elongation factor IWS1 to regulate target gene expression. Identification of BES1 and BZR1 target genes established a transcriptional network for BR response and crosstalk with other signaling pathways. Recent studies also revealed regulatory mechanisms of BRs in many developmental processes and regulation of BR biosynthesis. Here we provide an overview and discuss some of the most recent progress in the regulation of BR signaling and biosynthesis pathways.