ABC1激酶基因OsABC1K8调控水稻种子大小的分子机制

Rice is one of the most important food crops worldwide. Seed size is a key determinant of rice yield. To study the molecular mechanisms underlying regulation of rice seed size is extremely important for both genetic dissection of rice seed development and molecular breeding to improve rice yield. ABC1 (Activity of bc1 complex) kinases are newly found protein kinases, which are mainly located in chloroplasts or mitochondria in plants. In previous studies, we demonstrated that the chloroplast ABC1-kinase gene, OsABC1K8, is a key regulator of rice seed size by mutant analysis and over-expression (OE) assay. However, the physiological, biochemical and molecular mechanisms by which the gene controls rice seed size is still unknown. In this project, we will deep investigate the physiological mechanism by which OsABC1K8 modulates rice seed development using obtained mutant, OE and promoter-GUS plants and histological and physiological approaches, and identify the regulation network of the gene by RNA-seq analysis in combined with yeast two-hybrid screening. Our task is to illustrate the molecular mechanism by which OsABC1K8 controls rice grain shape, and provide new gene resources for rice high-yield molecular breeding. This study will also help to dissect the genetic mechanisms underlying crop seed development.

水稻是重要的粮食作物，种子大小是决定水稻产量的最重要因素之一。研究水稻种子大小调控的分子机制，对于解析水稻种子发育机理以及通过分子育种提高水稻产量具有重要意义。ABC1（Activity of bc1 complex）激酶是近年来新发现的一类蛋白质激酶，主要分布在植物叶绿体及线粒体内。我们前期通过突变体分析和过表达证明，水稻叶绿体ABC1激酶基因OsABC1K8对种子大小具有显著的调控作用，但该基因调控水稻种子大小的生理生化及分子机制尚不清楚。本项目拟以已经获得的OsABC1K8突变体、过表达和启动子-GUS株系为材料，利用组织学和生理学手段深入阐明OsABC1K8调控水稻种子发育的生理机制，并通过RNA-seq转录组测序结合酵母双杂交筛选互作蛋白鉴定该基因的作用网络。以期阐明OsABC1K8控制水稻粒形的分子机理，为分子育种提供新基因资源，同时也为解析作物种子发育的遗传机理提供理论依据。

种子大小是决定水稻产量的最重要因素之一。目前，我们对于水稻种子大小调控机制的认识仍不够全面。ABC1激酶是一类新发现的蛋白质激酶，其成员普遍存在于原核和真核生物中。前期研究表明，水稻叶绿体ABC1激酶基因OsABC1K8对种子大小具有显著的调控作用。本项目以过表达、RNA干扰株系等为材料，利用植物生理学和基因组学技术手段，阐明OsABC1K8调控水稻种子发育的生理和分子机制。OsABC1K8过表达植株抽穗前颖壳大于野生型，而RNAi植株小于野生型。过表达植株颖壳外表皮细胞长于野生型、横切面外层薄壁组织细胞数大于野生型，而RNAi植株具有相反的表型。过表达植株叶片光合产物的积累和输出以及籽粒灌浆速率显著高于对照。OsABC1K8的表达量分别随着颖壳和胚乳的发育过程呈现先上升后下降的趋势。转录组测序分析在RNAi和野生型植株叶片中筛选出204个差异表达基因，而在穗中筛选出150个差异表达基因。GO富集分析表明，OsABC1K8可能参与叶绿体氧化还原过程。酵母双杂交筛选共鉴定出12个互作蛋白，其中5个为未知或推定蛋白，其余7个分别为叶绿体肽甲硫氨酸亚砜还原酶B3、肉桂醇脱氢酶8C、异天冬氨酰肽酶/L-天冬酰胺酶2、叶绿体NAD(P)H-醌氧化还原酶亚基M、组织蛋白酶B样蛋白酶3同工型X1、受体丝氨酸/苏氨酸激酶PR5K和ATP依赖的Clp蛋白酶水解亚基6。对叶绿体肽甲硫氨酸亚砜还原酶B3和NAD(P)H-醌氧化还原酶亚基M进行的体内验证发现，两个蛋白均能与OsABC1K8在体内互作。此外，过表达植株叶片VE含量显著高于对照、IAA含量低于对照，而RNAi植株相反。因此，OsABC1K8可能通过调控组织生长素合成和对光氧化胁迫的抗性，促进颖壳发育和胚乳灌浆，进而影响水稻种子大小和粒重。这些结果为深入理解水稻种子发育机理以及OsABC1K8在水稻分子育种中的应用奠定了基础。