水稻穗型发育的分子调控机理研究

Panicle architecture is one of the important traits for yield of rice. The panicle development in rice involves in the process of transition of stem apical meristem into inflorescence meristem and occurrences of primary and secondary branch meristems, spikelet meristem, and floral meristem. The developmental processes of primary and secondary branches and spikelet determine the grain number per panicle. So far at least 28 genes involved in panicle architecture development have been cloned, but the relationships of genetic regulatory and molecular interaction of the genes are largely unclear. We have identified a rice mutant of larger panicle, large panicle 2 (lp2) with significantly increased numbers of primary and secondary branches, and grains. By a strategy of high-throughput sequencing of bulked segregants of the M2 line for this mutation, we rapidly mapped and isolated the target gene that encodes a bHLH transcription factor. In this study, we will conduct these studies: (1) analysis of the molecular functions of this gene by transformation of constructs of over-expression and RNA interference; (2) analysis of the expression patterns of LP2 and its downstream genes related to panicle development; (3) screening the target genes and interactors of LP2; (4) analysis of the variation of cytokinin in young panicles of lp2 mutant and wildtype rice; (5) revealing the genetic regulatory network in controlling the panicle development; (6) examination of the allelic variation of LP2 in rice varieties with different panicle size (grain number per panicle) and the association between the allelic variation and panicle size. In addition, based on the recessive genetic feature of lp2, we will use CRISPR/Cas9 system to modify this gene in elite rice varieties to create weak allele or loss-of-function mutation, in order to develop a new and high-efficient technology of molecular breeding in crops.

水稻穗型是最重要的产量性状之一。水稻穗型发育包括花序分生组织发生、一次和二次枝梗原基发生发育、小穗和颖花器官发生发育等过程，其中一次二次枝梗和小穗发育状态决定了穗大小和每穗颖花数。目前已克隆了至少28个水稻穗型或小穗发育相关的基因，但其调控和互作关系还不很清楚。我们从水稻获得了一个大穗型突变体lp2，其一次和二次枝梗数增多，每穗颖花数大幅增加（176.5%）。利用LP2lp2分离株系的分群混合高通量测序法，我们快速定位和克隆了目标基因为一个bHLH转录因子基因。本项目将研究该基因的生物学功能和遗传变异，分析对已知和未知的水稻穗建成发育相关基因的互作及其表达调控，揭示穗型发育的分子遗传调控网络。另一方面，基于其隐性遗传突变的特性，利用CRISPR/Cas9基因修饰系统对多个籼稻和粳稻优良品种的该基因进行功能弱化和功能缺失的修饰，培育更高产的新品种（系），探索新的高效作物分子育种技术方法。