Panicle architecture is a key determinant of grain yield in cereals, but the mechanisms governing panicle morphogenesis and organ development remain elusive. Here, we have identified a quantitative trait locus (qPA1) associated with panicle architecture using chromosome segment substitution lines from parents Nipponbare and 9311. The panicle length, branch number and grain number of Nipponbare were significantly higher than CSSL-9. Through map-based cloning and complementation tests, we confirmed that qPA1 was identical to SD1 (Semi Dwarf1), which encodes a gibberellin 20-oxidase enzyme participating in gibberellic acid (GA) biosynthesis. Transcript analysis revealed that SD1 was widely expressed during early panicle development. Analysis of sd1/osga20ox2 and gnp1/ osga20ox1 single and double mutants revealed that the two paralogous enzymes have non-redundant functions during panicle development, likely due to differences in spatiotemporal expression; GNP1 expression under control of the SD1 promoter could rescue the sd1 phenotype. The DELLA protein SLR1, a component of the GA signalling pathway, accumulated more highly in sd1 plants. We have demonstrated that SLR1 physically interacts with the meristem identity class I KNOTTED1-LIKE HOMEOBOX (KNOX) protein OSH1 to repress OSH1-mediated activation of downstream genes related to panicle development, providing a mechanistic link between gibberellin and panicle architecture morphogenesis.

中文翻译：

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赤霉素在水稻中协调由 DELLA-KNOX 信号介导的圆锥花序结构

穗结构是谷物产量的关键决定因素，但控制穗形态发生和器官发育的机制仍然难以捉摸。在这里，我们使用来自亲本日本晴和 9311 的染色体片段替换系鉴定了与穗结构相关的数量性状基因座 ( qPA1 )。日本晴的穗长、分枝数和粒数显着高于 CSSL-9。通过基于图谱的克隆和互补测试，我们证实qPA1与SD1 ( Semi Dwarf1 ) 相同，后者编码参与赤霉酸 (GA) 生物合成的赤霉素 20-氧化酶。成绩单分析显示SD1在早期穗发育过程中广泛表达。对sd1/osga20ox2和gnp1/osga20ox1单突变体和双突变体的分析表明，这两种旁系同源酶在穗发育过程中具有非冗余功能，可能是由于时空表达的差异；在SD1启动子控制下的GNP1表达可以挽救sd1表型。DELLA 蛋白 SLR1 是 GA 信号通路的一个组成部分，在sd1中积累得更多植物。我们已经证明 SLR1 与分生组织身份 I 类 KNOTTED1-LIKE HOMEOBOX (KNOX) 蛋白 OSH1 物理相互作用，以抑制 OSH1 介导的与穗发育相关的下游基因的激活，提供赤霉素和穗结构形态发生之间的机械联系。