线粒体逆行信号通路在植物胚胎发育过程中的功能分析

Embryogenesis in flowering plants covers a series of fundamental events as zygote division, establishment of apical--basal axis of polarity, cell division and differentiation, organ formation, and nutrition storage. The successful process of embryo development contributes to the formation of seed, the main product of crop. Data showed that mitochondrion plays essential role during the embryogenesis, however, the molecular mechanism how the mitochondrion is involved in embryogenesis has been kept largely unknown. Retrograde signaling from mitochondrion to nucleus and anti-retrograde signaling from nucleus to mitochondrion constitute important part of intra cell regulation network. The function and mechanism of mitochondrial retrograde signaling during plant development, especially in the embryogenesis, remains unrevealed, although wide and extensive studies on biological function of mitochondrion in yeast and nematode have been reported. Our data show that runtish is an Arabidopsis mutant with impaired embryogenesis due to deficiency in mitochondrial respiratory chain complex I. We further characterized MATF-1, the first identified transcription factor localized in mitochondrial outer membrane. Results indicate that the processing of MATF-1 protein is different from the wild type. It suggests that RUNTISH and MATF-1 are necessary players of mitochondrial retrograde signaling. How are RUNTISH and MATF-1 involved in mitochondrion--nucleus signal transduction? How does the mitochondrial retrograde signaling mediate embryogenesis in plants? What’s the regulation network between organelles and the nucleus in cell? In this project, we try to answer above important questions through our research with runtish, MATF-1 and other factors taking roles in mitochondrial retrograde signaling and embryogenesis. We believe that our study will shed more light for understanding biological function of mitochondrion and mechanism underlying organelle--nucleus regulation network, on the other hand, the results will also be significant for improvement and increase of crop yield.

高等植物胚胎发育包含合子延伸、极性建立、细胞分裂和分化、形态建成、营养物质贮存等重大事件，而这些都是种子形成的前提条件。研究表明，线粒体在植物胚胎发育过程中具有重要作用，但其中的分子遗传调控机制却不清楚。线粒体到细胞核的逆行信号通路和细胞核到线粒体的反逆行信号通路，构成了细胞内重要的信号网络。线粒体逆行信号通路在酵母和线虫中已得到广泛研究，而在植物中的研究却很匮乏。我们发现，拟南芥突变体runtish因线粒体功能受损而导致胚胎发育缺陷，MATF-1是定位于线粒体外膜的转录因子，MATF-1的加工方式在runtish突变体中发生改变，RUNTISH和MATF-1两者参与了线粒体逆行信号通路。在本课题中，我们将深入解析线粒体逆行信号网络对胚胎发育的调控作用。研究结果将有助于进一步认识细胞器—细胞核之间的双向信号网络和控制植物胚胎发育的调控机制，具有重要的理论意义和应用价值。

mitochondrion-mediated growth defect 1 (mid1)是Ds插入引起的拟南芥胚胎发育缺陷突变体。纯合突变体mid1的胚胎发育停滞在鱼雷胚时期，使晚期胚胎发育速度明显慢于野生型，种子成熟后体积小，萌发率下降，植株生长发育缓慢，体型矮小，生活周期明显延长。MID1是一个P类PPR家族的蛋白成员，参与nad2第一个内含子的剪切。MID1基因突变后导致线粒体呼吸链复合体I的结构和功能受到严重破坏，线粒体的超微结构出现损伤，部分线粒体的嵴塌陷。mid1突变体内积累了大量的H2O2，ATP的含量下降，细胞的生长和分裂均受影响。MID1与参与线粒体中RNA剪接的蛋白组分之间存在相互作用，共同参与内含子的剪接。MID1可能通过在线粒体中加工后再进入细胞核，影响下游基因的表达。而且，MID1在体内可与RNA结合形成胁迫小体，在线粒体受胁迫时，胁迫小体的数目明显增加，但其入核效率降低。该研究揭示MID1是线粒体与细胞核之间调控网络的关键组分，MID1在细胞核中是一个激活性的转录因子，可以对下游基因进行调控，mid1突变使线粒体发生损伤，从而激活了线粒体逆行信号通路，改变了相关核基因的表达，重塑了发育程序，影响了拟南芥的胚胎和植株发育。