New Phytol|中科院遗传发育所王永红研究员和浙大吴殿星教授在LAZY2控制水稻分蘖角研究机制中取得新成果
水稻（Oryza sativa）分蘖角是实现理想株型和高产的关键因素。然而，水稻分蘖角的分子机制尚不清楚。
我们鉴定了一个新的水稻分蘖角突变体lazy2（la2），并通过图位克隆分离了la2的致病基因。通过生化、分子生物学和遗传学研究，阐明了LA2参与分蘖角调控的机制。
la2突变体具有较大的分蘖角，植株向重力性减弱，生长素分布不对称。我们发现，在la2的重力感应叶鞘基细胞中，淀粉体中的淀粉颗粒完全丢失，而对种子发育没有影响。LA2编码一种新的叶绿体蛋白，能与淀粉生物合成酶水稻质体磷酸葡萄糖变位酶（OspPGM）相互作用，调节水稻地上部重力感应细胞的淀粉生物合成。遗传分析表明，LA2通过作用于LA1的上游调节生长素的侧向运输，从而调节地上部的向重力性和分蘖角。
我们的研究揭示了LA2通过特异性调控重力感应细胞中淀粉的生物合成，作为一种新型的水稻分蘖角调控因子，建立了淀粉-支撑石依赖的水稻分蘖角调控途径的框架，为水稻分蘖角调控网络提供了新的认识。
Rice (Oryza sativa) tiller angle is a key component for achieving ideal plant architecture and higher grain yield. However, the molecular mechanism underlying rice tiller angle remains elusive.
We characterized a novel rice tiller angle mutant lazy2 (la2) and isolated the causative gene LA2 through map-based cloning. Biochemical, molecular and genetic studies were conducted to elucidate the LA2-involved tiller angle regulatory mechanism.
The la2 mutant shows large tiller angle with impaired shoot gravitropism and defective asymmetric distribution of auxin. We found that starch granules in amyloplasts are completely lost in the gravity-sensing leaf sheath base cells of la2, whereas the seed development is not affected. LA2 encodes a novel chloroplastic protein that can interact with the starch biosynthetic enzyme Oryza sativa plastidic phosphoglucomutase (OspPGM) to regulate starch biosynthesis in rice shoot gravity-sensing cells. Genetic analysis showed that LA2 regulates shoot gravitropism and tiller angle by acting upstream of LA1 to mediate lateral auxin transport.
Our studies revealed that LA2 acts as a novel regulator of rice tiller angle by specifically regulating starch biosynthesis in gravity-sensing cells, and established the framework of the starch-statolith-dependent rice tiller angle regulatory pathway, providing new insights into the rice tiller angle regulatory network.
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