Sc复合体介导的基因等位抑制导致水稻杂种雄性不育的分子机制

Hybrids between the japonica and indica subspecies of Asian cultivated rice (Oryza sativa L.) have strong heterosis, but hybrid sterility hinders the utilization of such heterosis. We have cloned a major locus Sc for japonica-indica hybrid male sterility, and found that the indica allele had structural and copy number variations. In hybrids, the two or three tandem copies of two closely located genes Sc-i and Sc-iP in the indica allele act together to suppress the expression of the japonica allele gene Sc-j that is required for pollen development, thus causing abortion of Sc-j pollen. However, how Sc-i and Sc-iP interact to cause the allelic suppression of Sc-j remains unclear. In this project, we plan to elucidate the molecular mechanism of Sc-mediated hybrid incompatibility. Firstly, we transform Sc-i and Sc-iP separately and together to verify the hybrid sterile function of Sc-i and Sc-iP. Secondly, we further confirm the allelic suppression on the hybrid incompatibility through investigating the expression of Sc-j in the hybrids and transgenic plants with Sc-i and/or Sc-iP. Third, we will investigate relationship between Sc-j expression/silence and the epigenetic variations at the Sc-j promoter region in the hybrids and transgenic plants. Fourth, we study the interaction of Sc-i and Sc-iP proteins and the interaction of this complex with the Sc-j promoter. This project will elucidate how genomic variation plays a role on regulation of allelic suppression, and provide a potential approach via genome editing to break the reproductive barrier between plant subspecies/species, enabling use of hybrid vigor in crop hybrid breeding.

籼粳稻亚种间杂种具有强大的杂种优势，但其杂种不育性限制了杂种优势的利用。我们克隆了一个控制籼粳杂种雄性不育的座位Sc，发现籼稻Sc座位存在结构和拷贝数变异。2-3个串联重复的相邻基因Sc-i与Sc-iP共同作用抑制杂种中粳型基因Sc-j（花粉发育必需）的表达而导致Sc-j花粉不育。但籼粳Sc等位基因如何互作抑制Sc-j表达的分子机制仍不清楚。本项目拟在以上基础上开展以下工作：（1）以Sc-i和Sc-iP分别和共同转化粳稻，验证其杂种不育功能；（2）分析杂种和各转化体的Sc-j表达变化，确证Sc-j沉默与杂种不育的关系；（3）调查杂种和转化体的Sc-j表达与其启动子区的表观遗传修饰的关系；（4）检测Sc-i与Sc-iP蛋白互作及该复合体与Sc-j启动子区互作，阐明Sc-j等位抑制的机制。本研究将揭示基因组结构变异对等位基因表达调控的新机制，提供打破杂种生殖障碍的技术，促进作物杂种优势的利用。

籼粳稻亚种间杂种具有强大的杂种优势，但其杂种不育性限制了杂种优势的利用。我们前期克隆了一个控制籼粳杂种雄性不育的座位Sc，发现籼稻Sc座位存在结构和拷贝数变异（约28-kb 重复拷贝）。籼粳杂种F1中Sc等位基因的遗传互作会导致花粉发育必需基因Sc-j表达水平的大大下降，造成携带Sc-j等位基因的花粉选择性败。但籼粳Sc等位基因如何互作抑制Sc-j表达的分子机制仍不清楚。本项目旨在阐明Sc座位杂种不育的分子机制。在本项目的资助下，取得了以下几个主要进展：（1）发现每个28-kb 重复片段均包括一个Sc-i基因拷贝和三个籼稻特异的基因Sc-iP1、Sc-iP2和Sc-iP3，这四个基因表达模式相似，均定位与细胞核；（2）Sc-iP1与Sc-iP2、Sc-iP2与Sc-iP3、Sc-iP3与Sc-i、Sc-i与Sc-iP1之间发生互作，而Sc-iP1与Sc-iP3、Sc-iP2与Sc-i间不发生互作，表明这四个基因可以形成四基因复合体（Sc-iQ）；（3）在F1的背景下利用CRISPR/Cas9基因编辑技术分别敲除Sc-iP1、Sc-iP2和Sc-iP3，表明Sc-iP1、Sc-iP2和Sc-iP3是参与杂种不育的必须基因；（4）四基因串联重复片段转化T65引起杂种不育（5）Sc-i能与组蛋白去乙酰化酶OsHDAC1相互作用，且Sc蛋白复合体Sc-iQ可能与Sc-j基因的启动子和内含子互作。基于以上结果，本项目推测在杂种中Sci蛋白复合体可能通过与OsHDAC1互作，影响了Scj基因启动子或/与组蛋白的乙酰化修饰，进而等位抑制Scj基因的表达，最终导致杂种不育。本项目为阐明水稻杂种不育机理提供理论指导，为克服杂种不育提供有效策略和技术。