The U-box ubiquitin ligase TUD1 promotes brassinosteroid-induced GSK2 degradation in rice

Brassinosteroids(BRs)are a class of steroid hormones with great potential for use in crop improvement.De-repression is usually one of the key events in hormone signaling.However,how the stability of GSK2,the central negative regulator of BR signaling in rice(Oryza sativa),is regulated by BRs remains elusive.Here,we identify the U-box ubiquitin ligase TUD1 as a GSK2-interacting protein by yeast two-hybrid screening.We show that TUD1 is able to directly interact with GSK2 and ubiquitinate the protein.Phenotypes of the tud1 mutant are highly similar to those of plants with constitutively activated GSK2.Consistent with this finding,GSK2 protein accumulates in the tud1 mutant compared with the wild type.In addition,inhibition of BR synthesis promotes GSK2 accumulation and suppresses TUD1 stability.By contrast,BRs can induce GSK2 degradation but promote TUD1 accumulation.Furthermore,the GSK2 degradation process is largely impaired in tud1 in response to BR.In conclusion,our study demonstrates the role of TUD1 in BR-induced GSK2 degradation,thereby advancing our understanding of a critical step in the BR signaling pathway of rice.

Vital contribution of brassinosteroids to hypoxia-stimulated coleoptile elongation in submerged rice

The rapid elongation of rice(Oryza sativa)coleoptile is pivotal for the plant plumule to evade hypoxia stress induced by submergence,a condition often arising from overirrigation,ponding,rainstorms,or flooding.While brassinosteroids(BRs)are recognized for their diverse roles in plant growth and development,their influence on coleoptile elongation under hypoxic conditions remains largely unexplored.In this study,we demonstrate the significant requirement of BRs for coleoptile elongation in deep water.During coleoptile development,Glycogen Synthase Kinase3-Like Kinase2(GSK2),the central inhibitor of BR signaling in rice,undergoes substantial suppression in deep water but induction in air.In contrast,the dephosphorylated form of BRASSINAZOLE RESISTANT1(OsBZR1),representing the active form of the key BR signaling transcription factor,is induced in water but suppressed in air.Remarkably,the knockout of GSK3-like kinase genes significantly enhances coleoptile elongation in deep water,strongly indicating a vital contribution of BR response to hypoxia-stimulated coleoptile elongation.Transcriptome analysis uncovers both BR-associated and BR-independent hypoxia responses,implicating substance metabolism,redox reactions,abiotic stress responses,and crosstalk with other hormones in the regulation of BR-induced hypoxia responses.In summary,our findings suggest that rice plumules rapidly elongate coleoptiles through the activation of BR response in deep water,enabling them to escape from submergence-induced hypoxia stress.

油菜素甾醇调控水稻盐胁迫应答的作用研究

油菜素甾醇(BR)作为植物内源激素,广泛参与植物的生长发育过程及逆境应答。虽然BR调控生长发育的分子机制目前已相对清楚,但在水稻(Oryza sativa)中, BR在逆境反应中的功能还鲜有报道。该研究系统分析了BR在高盐胁迫过程中的作用,表明盐胁迫和逆境激素脱落酸可抑制BR合成基因D2和D11的表达,典型的BR缺陷突变体(如d2-2和d61-1)则表现出对盐胁迫敏感性增强。此外,通过对BR核心转录因子OsBZR1的过表达株系进行分析,发现BR可显著诱导OsBZR1的去磷酸化,盐胁迫对OsBZR1蛋白的积累水平和磷酸化状态均有调控作用。转录组数据分析表明,BR处理前后差异表达基因中有38.4%同时受到盐胁迫调控,其中91.5%受到BR和高盐一致调控,并显著富集在应激反应过程中。研究结果表明,BR正调控水稻的耐盐性,而盐胁迫通过抑制BR合成来限制水稻的生长。

The divergence of brassinosteroid sensitivity between rice subspecies involves natural variation conferring altered internal auto-binding of OsBSK2

Japonica/geng and indica/xian are two major rice(Oryza sativa)subspecies with multiple divergent traits,but how these traits are related and interact within each subspecies remains elusive.Brassinosteroids(BRs)are a class of steroid phytohormones that modulate many important agronomic traits in rice.Here,using different physiological assays,we revealed that japonica rice exhibits an overall lower BR sensitivity than indica.Extensive screening of BR signaling genes led to the identification of a set of genes distributed throughout the primary BR signaling pathway with divergent polymorphisms.Among these,we demonstrate that the C38/T variant in BR Signaling Kinase2(OsBSK2),causing the amino acid change P13L,plays a central role in mediating differential BR signaling in japonica and indica rice.OsBSK2in indica plays a greater role in BR signaling than OsB SK2in japonica by affecting the auto-binding and protein accumulation of OsBSK2.Finally,we determined that OsBSK2 is involved in a number of divergent traits in japonica relative to indica rice,including grain shape,tiller number,cold adaptation,and nitrogen-use efficiency.Our study suggests that the natural variation in OsB SK2 plays a key role in the divergence of BR signaling,which underlies multiple divergent traits between japonica and indica.