MSH1调控榨菜胞质雄性不育基因ORF220亚化学计量及育性回复机制

Cytoplasmic male sterility (CMS), as a maternally inherited trait that prevents the production of functional pollen, is widely used in hybrid breeding and currently, which is observed in > 150 plant species, with several conserved features in common.The mechanism on male sterility occurrence and fertility regulation could offer theoretical basis and new approach to hybrid heterosis. CMS has consistently been associated with expression of mitochondrial open reading frames (ORFs) that arise from rearrangements involving nonhomologous end-joining within the mitochondrial genome. MSH1 (Muts Homolog 1, homolog to the bacterial mismatch repair protein MutS) regulates mitochondrial genomic rearrangment in plant. Previously, we have identified CMS-associated ORF220 in CMS Brassica juncea and proof ORF220's function by using mitochondrially-targeted expression. In this project, we study substoichiometric shifting (SSS) of ORF220 in CMS, its maintainer fertile and spontaneous revertants lines of Brassica juncea, how MSH1 regulate SSS of ORF220 and fertility. We try to learn whether the CMS-associated mitochondrial genomic rearrangement has undergone SSS to suppress copy number of the ORF220 gene, providing a useful system for studying the reversibility of SSS and interplay of MSH1 in cytoplasmic male sterility induction and fertility reversion in Brassica juncea.

细胞质雄性不育是作物杂种优势利用的重要途径之一，其发生及育性调控机制的研究，可为杂种优势的利用提供理论基础及新策略。线粒体重组产生新ORF被认为是胞质雄性不育发生的原因，核编码的MSH1基因是调控线粒体重组的关键基因。课题组前期通过线粒体定位表达ORF220验证了其介导胞质雄性不育的功能。本项目在此基础上，从MSH1调控ORF220亚化学计量与育性相关性角度入手，运用遗传学、分子生物学和生物化学等手段，主要研究保持系、不育系及育性回复突变系中ORF220亚化学计量与育性转变的关系以及MSH1调控ORF220亚化学计量的机制等，试图解析MSH1如何调控线粒体基因组重组及ORF220亚化学计量改变、ORF220的亚化学计量改变如何调控育性的转变机制，从基因组水平上解析胞质雄性不育发生及育性调控的新机制。

细胞质雄性不育是作物杂种优势利用的重要途径。芥菜类蔬菜属于常异花植物，自交亲和指数高，细胞质雄性不育是芥菜类蔬菜杂种优势利用的主要途径。本研究首次在十字花科作物中鉴定到芥菜细胞质雄性不育系的育性回复突变系（Revertant），育性回复正常，但不能恢复不育系的育性，育性回复突变系是由不育系突变而来，与不育系相比是典型的野生型与突变体的遗传背景。在此基础上发现，ORF220亚化学计量变化或者拷贝数变化（substoichiometric shift，SSS）与保持系、不育系和育性回复突变系的育性转变相关。然后，通过线粒体定位表达技术验证了ORF220 的胞质雄性不育生物学功能，成为线粒体定位表达ORFs基因人工创制胞质雄性不育系的新方法。核基因MutS HOMOLOG1（MSH1）是调控线粒体基因组重组和SSS的关键基因，我们通过构建芥菜MSH1-RNAi系，发现MSH1抑制表达后，ORF220基因表现出SSS现象，转基因后代中ORF220拷贝数增加和ORF220基因表达上调的植株表现为雄性不育现象。我们提出了MSH1通过调控胞质雄性不育基因ORF220亚化学计量变化（或者拷贝数变化）介导雄性不育和育性回复突变的机制，主要结果发表在Journal of Experimental Botany（2016）、Plant Biology（2016）等杂志上，部分结果是发表在Nature Genetics（2016）上论文的内容。细胞质雄性不育发生与育性回复突变机制的揭示，为基于核质互作调控雄性不育发生和育性回复突变机制的优异种质资源创新提供理论依据，同时可为其它植物育性转变研究提供新思路和新策略。