Hu Anqi, Zhao Qiaoqiao, Chen Li, Zhao Jinping, Wang Yuehua, Feng Kuiliang, Wu Ling, Xie Miao, Zhou Xuemei, Xiao Langtao, Ming Zhenhua, Zhang Meng, Yao Ruifeng
State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan Provincial Key Laboratory of Plant Functional Genomics and Developmental Regulation, College of Biology, Hunan University, Changsha, China.
State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bio Resources, Guangxi Key Laboratory for Sugarcane Biology, College of Life Science and Technology, Guangxi University, Nanning, China.
Front Plant Sci. 2021 Nov 11;12:747160. doi: 10.3389/fpls.2021.747160. eCollection 2021.
Strigolactones (SLs) are a class of important plant hormones mainly regulating plant architecture such as branching, which is crucial for crop yield. It is valuable to study SL signaling pathway and its physiological function in sugarcane, the most important sugar crop, for further molecular breeding. Here, two putative SL receptors SsD14a/b and the interacting F-box protein SsMAX2 were identified in . SL induced both SsD14a and SsD14b to interact with SsMAX2 in yeast. SsD14a, but not SsD14b, could bind with AtMAX2 and AtSMXL7/SsSMXL7. Overexpression of or rescued the increased branching phenotypes of or mutants, respectively. Moreover, the crystal structure of N-terminal truncated SsD14a was solved, with an overall structure identical to AtD14 and OsD14 in the open state, consistent with its conserved branching suppression capacity in . In line with the biochemical observations, could not completely complement in although these two SsD14 proteins have almost identical primary sequences except for very few residues. Complement with the combination of and still failed to rescue the double mutant multi-branching phenotype, indicating SsD14b-AtSMXL7 complex formation is required for regulating branching. Mutagenesis analyses revealed that residue R310 at α10 helix of SsD14a was crucial for the binding with SsSMXL7/AtSMXL7 but not SsMAX2. The site-equivalent single-residue P304R substitution enabled SsD14b to bind with AtMAX2 and AtSMXL7/SsSMXL7 and to rescue the phenotype of together with SsMAX2. Moreover, this conserved Arg residue across species including rice and determined the activity of SL receptors through maintaining their interaction with SMXL repressors. Taken together, our work identified conserved and divergent strigolactone receptors in sugarcane core SL signaling pathway and revealed a key residue crucial for plant branching control.
独脚金内酯（SLs）是一类重要的植物激素，主要调控植物的株型，如分枝，这对作物产量至关重要。研究甘蔗（最重要的糖料作物）中SL信号通路及其生理功能，对进一步的分子育种具有重要价值。在此，在甘蔗中鉴定出两个假定的SL受体SsD14a/b以及相互作用的F-box蛋白SsMAX2。SL在酵母中诱导SsD14a和SsD14b均与SsMAX2相互作用。SsD14a能与AtMAX2以及AtSMXL7/SsSMXL7结合，但SsD14b不能。分别过表达SsD14a或SsD14b可挽救MAX2或SMXL7突变体增加的分枝表型。此外，解析了N端截短的SsD14a的晶体结构，其整体结构在开放状态下与AtD14和OsD14相同，这与其在甘蔗中保守的分枝抑制能力一致。与生化观察结果一致，尽管这两个SsD14蛋白除了极少数残基外具有几乎相同的一级序列，但SsD14b不能完全互补MAX2突变体。与SsMAX2组合互补仍未能挽救MAX2-SMXL7双突变体的多分枝表型，表明调控分枝需要形成SsD14b-AtSMXL7复合物。诱变分析表明，SsD14a的α10螺旋上的R310残基对于与SsSMXL7/AtSMXL7结合至关重要，但对与SsMAX2结合不重要。位点等效的单残基P304R替换使SsD14b能够与AtMAX2以及AtSMXL7/SsSMXL7结合，并与SsMAX2一起挽救MAX2突变体的表型。此外，包括水稻和甘蔗在内的跨物种保守的精氨酸残基通过维持其与SMXL阻遏物的相互作用来决定SL受体的活性。综上所述，我们的工作在甘蔗核心SL信号通路中鉴定出保守和不同的独脚金内酯受体，并揭示了对植物分枝控制至关重要的关键残基。
