水稻LA2基因调控分蘖角度的作用机理研究

Tiller angle is an important factor determining rice yield, lodging resistance and disease occurrence of rice plants. As one of the key factors determining plant architecture, rice tiller angle is of great concern to rice breeders. However, the molecular mechanism of rice tiller angle is unclear, and few genes were cloned. A natural spread tiller angle mutant (la2) was found in the field of an indica rice variety Xiangwanxian No.13. Our previous study showed that this tiller-spreading phenotype was caused by reduced shoot gravitropism and controlled by a pair of recessive nuclear gene (LA2). The LA2 have been fine-mapped to a 31Kb region on the short arm of chromosome 2. After sequencing of this region, ORF3 was predicted to be the candidate gene of LA2, and was confirmed by complementation test and CRISPR/Cas9 gene editing. Bioinformatics analysis implied that LA2 is a new gene with unknown function, which might encode a transcription factor. Based on the above results, we further plans to dissect the basic characteristics of LA2 and investigate the molecular regulatory of LA2 through gravity response. The results will help to further elucidate the molecular mechanism of rice architecture, and also provide new gene for breeding rice varieties with ideal plant type.

分蘖角度是影响水稻产量、抗倒性以及病害发生的重要因素，在育种实践中被重点关注，但目前对其遗传调控机理仍不清楚。本实验室从籼稻品种中获得一个分蘖角度明显增大的突变体la2，其突变表型是由于重力反应下降引起的；该散生突变受一对隐性核基因控制，目前已完成目标基因的定位和候选基因预测，并通过互补分析和CRISPR/Cas9技术验证了候选基因的功能；通过生物信息学分析预测该基因是一个功能未知的新基因(命名为LA2)，可能编码转录因子。本项目拟在以上研究基础上，分析生长素的极性运输等生理过程，揭示LA2控制水稻分蘖角度的生理基础；通过荧光定量PCR、亚细胞定位、转录激活等分析，剖析LA2基因及其编码蛋白的基本特性；通过转录组测序、染色质免疫共沉淀等分析，阐明LA2基因参与重力响应调控水稻分蘖角度的分子机制。研究结果不仅为阐明水稻株型调控的分子机理提供依据，而且为分子育种培育理想株型水稻品种提供新基因。

改良水稻株型，增强光合效率是提高水稻单产的重要途径。分蘖角度是株型的重要构成因素，直接影响水稻的种植密度、光合效率、抗倒性以及病虫害发生情况，最终影响水稻的产量和收获指数。尽管这一性状在育种实践中被重点关注，多个控制分蘖角度的基因已被克隆，但目前对其分子机制的研究仍相对滞后，分蘖角度基因如何影响水稻产量仍不清楚。本研究发掘到一个分蘖角度明显增大的突变体lta1，其结实率和产量明显下降。组织切片结果表明，突变体分蘖基部远地端的细胞长度显著长于野生型。重力诱导实验发现，突变体茎秆内的生长素侧向运输受阻，导致重力反应削弱，从而表现出分蘖角度增大的表型。图位克隆将LTA1基因定位于水稻第2染色体，编码一个具有保守YbaB DNA结合结构域的叶绿体蛋白，遗传互补和基因敲除实验均证明了LTA1基因在调控分蘖角度和产量中的作用。荧光定量PCR结果表明，该基因主要在叶片、叶鞘等光合组织中表达。通过观察叶绿体超微结构，发现lta1突变体的叶绿体膨大近圆形，且叶绿体内的片层结构分布更松散，叶绿素含量和光合作用速率也显著下降。研究结果为进一步阐明水稻株型的遗传调控机制，精准定向改良水稻株型和提高产量提供了理论基础。