Rice SEPALLATA Genes OsMADS5and OsMADS34 Cooperate to Limit Inflorescence Branching by Repressing the TERMINAL FLOWER1-like Gene RCN4

背景回顾：The spatiotemporal control of meristem identity is critical for determining inflorescence architecture, and thus yield, of cereal plants. 

提出问题：However, the precise mechanisms underlying inflorescence and spikelet meristem determinacy in cereals are still largely unclear. 

主要研究：We have generated loss-of-function and overexpression mutants of the paralogous OsMADS5 and OsMADS34 genes in rice (Oryza sativa), and analysed their panicle phenotypes. 

结果1-OsMADS5和OsMAD34直接下游RCN4：Using chromatin immunoprecipitation, electrophoretic mobility-shift and dual‑luciferase assays, we have also identified RICE CENTRORADIALIS 4 (RCN4), a TFL1-like gene, as a direct downstream target of both OsMADS proteins, and have analysed RCN4 mutants. 

结果2-osmads5 osmads34突变体：The osmads5 osmads34 mutant lines had significantly enhanced panicle branching with increased secondary, and even tertiary and quaternary, branches, compared to wild type and osmads34 plants. 

结果3-敲除RCN4恢复osmads34突变体表型：The osmads34 mutant phenotype could largely be rescued by also knocking out RCN4. 

结果4-过表达RCN4：Moreover, transgenic panicles overexpressing RCN4 had significantly increased branching, and initiated development of ~7× more spikelets than wild type. 

结论：Our results reveal a role for OsMADS5 in panicle development, and show that OsMADS5 and OsMADS34 play similar functions in limiting branching and promoting the transition to spikelet meristem identity, in part by repressing RCN4 expression. 

展望：These findings provide new insights to better understand the molecular regulation of rice inflorescence architecture.

 摘 要 

分生组织的时空调控对于决定谷类作物的花序结构及产量都至关重要。但是，对于谷类作物中花序和小穗分生组织确定性的精确调控机制在很大程度上都是未知的。本文中，作者构建了水稻OsMADS5和OsMADS34基因的功能缺失突变和过表达株系，并分析了其在圆锥花序中产生的表型。利用染色体免疫共沉淀、EMSA凝胶迁移以及双荧光素酶实验，作者在水稻中鉴定到了一个类TFL1基因RCN4，该基因是上述两个OsMADS基因的直接下游靶标，作者进一步分析了RCN4的突变体。与野生型和osmads34突变体相比，osmads5 osmads34突变体株系具有显著增加的圆锥花序分枝，其第二，甚至是第三、第四级分枝数目增多。osmads34突变体的表型能够通过敲除RCN4基因进行拯救。此外，过表达RCN4基因的转基因株系具有分枝增加的圆锥花序，并且其花序上起始的小穗数量约是野生型的7倍之多。本文的研究结果揭示了OsMADS5在水稻的花序发育中的作用，并且发现OsMADS5和OsMADS34在限制分枝和促进向小穗分生组织的转变等方面具有类似的功能，均是部分通过抑制RCN4基因的表达来发挥作用。这些发现为我们进一步理解水稻花序结构的分子调控提供了新的视野。

 通讯作者 

** 张大兵 **