Starch biosynthesis in gravity-sensing tissues of rice shoot determines the magnitude of rice shoot gravitropism and thus tiller angle. However, the molecular mechanism underlying starch biosynthesis in rice gravity-sensing tissues is still unclear. We characterized a novel tiller angle gene LAZY3 (LA3) in rice through map-based cloning. Biochemical, molecular and genetic studies further demonstrated the essential roles of LA3 in gravity perception of rice shoot and tiller angle control. The shoot gravitropism and lateral auxin transport were defective in la3 mutant upon gravistimulation. We showed that LA3 encodes a chloroplast-localized tryptophan-rich protein associated with starch granules via Tryptophan-rich region (TRR) domain. Moreover, LA3 could interact with the starch biosynthesis regulator LA2, determining starch granule formation in shoot gravity-sensing tissues. LA3 and LA2 negatively regulate tiller angle in the same pathway acting upstream of LA1 to mediate asymmetric distribution of auxin. Our study defined LA3 as an indispensable factor of starch biosynthesis in rice gravity-sensing tissues that greatly broadens current understanding in the molecular mechanisms underlying the starch granule formation in gravity-sensing tissues, and provides new insights into the regulatory mechanism of shoot gravitropism and rice tiller angle.

中文翻译：

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LAZY3 与 LAZY2 相互作用通过调节水稻茎部重力感知来调节分蘖角度

水稻地上部重力感应组织中的淀粉生物合成决定了水稻地上部向重力性的大小，从而决定了分蘖角度。然而，水稻重力感应组织中淀粉生物合成的分子机制仍不清楚。我们通过基于图谱的克隆对水稻中一个新的分蘖角基因LAZY3 ( LA3 ) 进行了表征。生化、分子和遗传学研究进一步证明了LA3在水稻新梢重力感知和分蘖角度控制中的重要作用。在重力刺激下， la3突变体的茎向重力性和横向生长素运输存在缺陷。我们证明了LA3通过富含色氨酸的区域 (TRR) 域编码与淀粉颗粒相关的叶绿体定位的富含色氨酸的蛋白质。此外，LA3 可以与淀粉生物合成调节剂 LA2 相互作用，决定芽的重力感应组织中淀粉颗粒的形成。LA3和LA2在作用于LA1上游的同一通路中负向调节分蘖角，以介导生长素的不对称分布。我们的研究将 LA3 定义为水稻重力感应组织中淀粉生物合成不可或缺的因子，极大地拓宽了目前对重力感应组织中淀粉颗粒形成的分子机制的理解，并为芽向地性和水稻调控机制提供了新的见解舵角。