The effects of DELLAs on growth change with developmental stage and brassinosteroid levels

Brassinosteroid decreases cadmium accumulation via regulating gibberellic acid accumulation and Cd fixation capacity of root cell wall in rice (Oryza sativa)

The precise mechanism behind the association between plants' reactions to cadmium (Cd) stress and brassinosteroid (BR) remains unclear. In the current investigation, Cd stress quickly increased the endogenous BR concentration in the rice roots. Exogenous BR also increased the hemicellulose level in the root cell wall, which in turn increased its capacity to bind Cd. Simultaneously, the transcription level of genes responsible for root Cd absorption was decreased, including Natural Resistance-Associated Macrophage Protein 1/5 (OsNRAMP1/5) and a major facilitator superfamily gene called OsCd1. Ultimately, the increased expression of Heavy Metal ATPase 3 (OsHMA3) and the decreased expression of OsHMA2, which was in charge of separating Cd into vacuoles and translocating Cd to the shoots, respectively, led to a decrease in the amount of Cd that accumulated in the rice shoots. In contrast, transgenic rice lines overexpressing OsGSK2 (a negative regulator in BR signaling) accumulated more Cd, while OsGSK2 RNA interference (RNAi) rice line accumulated less Cd. Furthermore, BR increased endogenous Gibberellic acid (GA) level, and applying GA could replicate its alleviative effect. Taken together, BR decreased Cd accumulation in rice by mediating the cell wall's fixation capacity to Cd, which might relied on the buildup of the GA.

Cytological, Phytohormone, and Transcriptome Analyses Provide Insights into Persimmon Fruit Shape Formation (Diospyros kaki Thunb.)

Fruit shape is an important external feature when consumers choose their preferred fruit varieties. Studying persimmon (Diospyros kaki Thunb.) fruit shape is beneficial to increasing its commodity value. However, research on persimmon fruit shape is still in the initial stage. In this study, the mechanism of fruit shape formation was studied by cytological observations, phytohormone assays, and transcriptome analysis using the long fruit and flat fruit produced by 'Yaoxianwuhua' hermaphroditic flowers. The results showed that stage 2-3 (June 11-June 25) was the critical period for persimmon fruit shape formation. Persimmon fruit shape is determined by cell number in the transverse direction and cell length in the longitudinal direction. High IAA, GA4, ZT, and BR levels may promote long fruit formation by promoting cell elongation in the longitudinal direction, and high GA3 and ABA levels may be more conducive to flat fruit formation by increasing the cell number in the transverse direction and inhibiting cell elongation in the longitudinal direction, respectively. Thirty-two DEGs related to phytohormone biosynthesis and signaling pathways and nine DEGs related to cell division and cell expansion may be involved in the persimmon fruit shape formation process. These results provide valuable information for regulatory mechanism research on persimmon fruit formation.

OsWRKY78 regulates panicle exsertion via gibberellin signaling pathway in rice

Panicle exsertion is one of the crucial agronomic traits in rice (Oryza sativa). Shortening of panicle exsertion often leads to panicle enclosure and severely reduces seed production. Gibberellin (GA) plays important roles in regulating panicle exsertion. However, the underlying mechanism and the relative regulatory network remain elusive. Here, we characterized the oswrky78 mutant showing severe panicle enclosure, and found that the defect of oswrky78 is caused by decreased bioactive GA contents. Biochemical analysis demonstrates that OsWRKY78 can directly activate GA biosynthesis and indirectly suppress GA metabolism. Moreover, we found OsWRKY78 can interact with and be phosphorylated by mitogen-activated protein kinase (MAPK) kinase OsMAPK6, and this phosphorylation can enhance OsWRKY78 stability and is necessary for its biological function. Taken together, these results not only reveal the critical function of OsWRKY78, but also reveal its mechanism via mediating crosstalk between MAPK and the GA signaling pathway in regulating panicle exsertion.

Comparative transcriptome profiling reveals the multiple levels of crosstalk in phytohormone networks in Brassica napus

Plant hormones are the intrinsic factors that control plant development. The integration of different phytohormone pathways in a complex network of synergistic, antagonistic and additive interactions has been elucidated in model plants. However, the systemic level of transcriptional responses to hormone crosstalk in Brassica napus is largely unknown. Here, we present an in-depth temporal-resolution study of the transcriptomes of the seven hormones in B. napus seedlings. Differentially expressed gene analysis revealed few common target genes that co-regulated (up- and down-regulated) by seven hormones; instead, different hormones appear to regulate distinct members of protein families. We then constructed the regulatory networks between the seven hormones side by side, which allowed us to identify key genes and transcription factors that regulate the hormone crosstalk in B. napus. Using this dataset, we uncovered a novel crosstalk between gibberellin and cytokinin in which cytokinin homeostasis was mediated by RGA-related CKXs expression. Moreover, the modulation of gibberellin metabolism by the identified key transcription factors was confirmed in B. napus. Furthermore, all data were available online from http://yanglab.hzau.edu.cn/BnTIR/hormone. Our study reveals an integrated hormone crosstalk network in Brassica napus, which also provides a versatile resource for future hormone studies in plant species.

SlCESTA Is a Brassinosteroid-Regulated bHLH Transcription Factor of Tomato That Promotes Chilling Tolerance and Fruit Growth When Over-Expressed

Brassinosteroids (BRs) are required for various aspects of plant growth and development, but also participate in stress responses. The hormones convey their activity through transcriptional regulation and posttranslational modification of transcription factors and one class are basic helix-loop-helix (bHLH) proteins of the BR Enhanced Expression (BEE) subfamily, which in Arabidopsis thaliana include BEE1-3 and CESTA (CES). CES and the BEEs promote the expression of different BR-responsive genes, including genes encoding gibberellin (GA) biosynthetic and catabolizing enzymes, as well as cold-responsive genes. Interestingly, in terms of an application, CES could promote both fruit growth and cold stress tolerance when over-expressed in A. thaliana and here it was investigated, if this function is conserved in the fruit crop Solanum lycopersicum (cultivated tomato). Based on amino acid sequence similarity and the presence of regulatory motifs, a CES orthologue of S. lycopersicum, SlCES, was identified and the effects of its over-expression were analysed in tomato. This showed that SlCES, like AtCES, was re-localized to nuclear bodies in response to BR signaling activation and that it effected GA homeostasis, with related phenotypes, when over-expressed. In addition, over-expression lines showed an increased chilling tolerance and had altered fruit characteristics. The possibilities and potential limitations of a gain of SlCES function as a breeding strategy for tomato are discussed.

Interactions of Gibberellins with Phytohormones and Their Role in Stress Responses

Gibberellins are amongst the main plant growth regulators. Discovered over a century ago, the interest in gibberellins research is growing due to their current and potential applications in crop production and their role in the responses to environmental stresses. In the present review, the current knowledge on gibberellins’ homeostasis and modes of action is outlined. Besides this, the complex interrelations between gibberellins and other plant growth regulators are also described, providing an intricate network of interactions that ultimately drives towards precise and specific gene expression. Thus, genes and proteins identified as being involved in gibberellin responses in model and non-model species are highlighted. Furthermore, the molecular mechanisms governing the gibberellins’ relation to stress responses are also depicted. This review aims to provide a comprehensive picture of the state-of-the-art of the current perceptions of the interactions of gibberellins with other phytohormones, and their responses to plant stresses, thus allowing for the identification of the specific mechanisms involved. This knowledge will help us to improve our understanding of gibberellins’ biology, and might help increase the biotechnological toolbox needed to refine plant resilience, particularly under a climate change scenario.

Auxin promotion of seedling growth via ARF5 is dependent on the brassinosteroid-regulated transcription factors BES1 and BEH4

Seedlings must continually calibrate their growth in response to the environment. Auxin and brassinosteroids (BRs) are plant hormones that work together to control growth responses during photomorphogenesis. We used our previous analysis of promoter architecture in an auxin and BR target gene to guide our investigation into the broader molecular bases and biological relevance of transcriptional co-regulation by these hormones. We found that the auxin-regulated transcription factor Auxin Responsive Factor 5 (ARF5) and the brassinosteroid-regulated transcription factor BRI1-EMS-Suppressor 1/Brassinazole Resistant 2 (BES1) co-regulated a subset of growth-promoting genes via conserved bipartite cis-regulatory elements. Moreover, ARF5 binding to DNA could be enriched by increasing BES1 levels. The evolutionary loss of bipartite elements in promoters results in loss of hormone responsiveness. We also identified another member of the BES1/BZR1 family called BEH4 that acts partially redundantly with BES1 to regulate seedling growth. Double mutant analysis showed that BEH4 and not BZR1 were required alongside BES1 for normal auxin response during early seedling development. We propose that an ARF5-BES1/BEH4 transcriptional module acts to promote growth via modulation of a diverse set of growth-associated genes.

Brassinosteroids, the Sixth Class of Phytohormones: A Molecular View from the Discovery to Hormonal Interactions in Plant Development and Stress Adaptation

Phytohormones are natural chemical messengers that play critical roles in the regulation of plant growth and development as well as responses to biotic and abiotic stress factors, maintaining plant homeostasis, and allowing adaptation to environmental changes. The discovery of a new class of phytohormones, the brassinosteroids (BRs), almost 40 years ago opened a new era for the studies of plant growth and development and introduced new perspectives in the regulation of agronomic traits through their use in agriculture. BRs are a group of hormones with significant growth regulatory activity that act independently and in conjunction with other phytohormones to control different BR-regulated activities. Genetic and molecular research has increased our understanding of how BRs and their cross-talk with other phytohormones control several physiological and developmental processes. The present article provides an overview of BRs' discovery as well as recent findings on their interactions with other phytohormones at the transcriptional and post-transcriptional levels, in addition to clarifying how their network works to modulate plant growth, development, and responses to biotic and abiotic stresses.

MdBZR1 and MdBZR1-2like Transcription Factors Improves Salt Tolerance by Regulating Gibberellin Biosynthesis in Apple

Brassinosteroids (BRs) are a group of plant steroid hormones that play important roles in regulating plant development. In addition, BRs show considerable functional redundancy with other plant hormones such as gibberellins (GAs). BRASSINAZOLE RESISTANT1 (BZR1) and BRI1-EMS-SUPPRESSOR1 (BES1) transcription factors are negative feedback regulators of BR biosynthesis. This study provides evidence for the roles of MdBZR1 and MdBZR1-2like in promoting GA production. These results also show that BRs regulate GA biosynthesis to improve salt tolerance in apple calli. Moreover, this research proposes a regulatory model, in which MdBZR1 and MdBZR1-2like bind to the promoters of GA biosynthetic genes to regulate their expression in a BR-dependent manner. The expression of key GA biosynthetic genes, MdGA20ox1, MdGA20ox2, and MdGA3ox1 in yeast helps to maintain normal growth even under intense salt stress. In summary, this study underscores the roles of MdBZR1 and MdBZR1-2like in improving salt tolerance by regulating GA biosynthesis in apple calli.

Regulation of BZR1 in fruit ripening revealed by iTRAQ proteomics analysis

Fruit ripening is a complex and genetically programmed process. Brassinosteroids (BRs) play an essential role in plant growth and development, including fruit ripening. As a central component of BR signaling, the transcription factor BZR1 is involved in fruit development in tomato. However, the transcriptional network through which BZR1 regulates fruit ripening is mostly unknown. In this study, we use isobaric tags for relative and absolute quantitation (iTRAQ) labeling technology to explore important proteins regulated by BZR1 in two independent tomato transgenic lines over-expressing BZR1-1D at four ripening stages, identifying 411 differentially expressed proteins. These proteins were implicated in light reaction, plant hormone pathways and cell-wall-related metabolism, etc. The ‘light reaction’ metabolic pathway was identified as a markedly enhanced pathway by BZR1 during tomato fruit ripening. The protein level of a probable 2-oxoglutarate-dependent dioxygenase 2-ODD2, involved in gibberellin biosynthesis was significantly increased at all four developmental and ripening stages. The results reveal molecular links between BR signaling pathway and downstream components involved in multiple ripening-associated events during tomato fruit ripening, which will provide new insights into the molecular mechanisms underlying tomato ripening regulatory networks, and be potential in understanding BR-regulated fruit ripening.

The molecular circuitry of brassinosteroid signaling

Because they are tethered in space, plants have to make the most of their local growth environment. In order to grow in an ever-changing environment, plants constantly remodel their shapes. This adaptive attribute requires the orchestration of complex environmental signals at the cellular and organismal levels. A battery of small molecules, classically known as phytohormones, allows plants to change their body plan by using highly integrated signaling networks and transcriptional cascades. Amongst these hormones, brassinosteroids (BRs), the polyhydroxylated steroid of plants, influence plant responsiveness to the local environment and exquisitely promote, or interfere with, many aspects of plant development. The molecular circuits that wire steroid signals at the cell surface to the promoters of thousands of genes in the nucleus have been defined in the past decade. This review recapitulates how the transduction of BR signals impacts the temporally unfolding programs of plant growth. First, we summarize the paradigmatic BR signaling pathway acting primarily in cellular expansion. Secondly, we describe the current wiring diagram and the temporal dynamics of the BR signal transduction network. And finally we provide an overview of how key players in BR signaling act as molecular gates to transduce BR signals onto other signaling pathways.