拟南芥叶绿体蛋白SL1功能研究及其调控叶绿体发育的分子机制

Photosynthesis maintains atmospheric oxygen levels and supplies all of the organic compounds and most of the energy necessary for life on Earth. Chloroplasts are semiautonomous, photosynthetic organelles with their own genome. The development of chloroplasts is important for plant growth and development. Chloroplast genes expression is regulated through a special process called RNA editing, whose mechanism is largely unknown. To investigate chloroplast gene expression regulation, an Arabidopsis T-DNA insertion mutant library was screened, a seedling lethal mutant sl1 was identified, and the relevant gene SL1 was cloned. The results showed SL1 gene expressed in various tissues, SL1 protein localized into chloroplast, and was involved in chloroplast gene expression regulation. Based on these results, we intend to characterize the physiological function of SL1 and reveal its molecular mechanism, by way of combining genetics, biochemistry, cell biology, molecular biology and other methods. Elucidation of the function and physiological significance of SL1 and its related genes should reveal the underlying mechanisms of chloroplast gene expression regulation and chloroplast development. In addition，control and enhancement of plastid gene expression and environmental acclimation will improve the chloroplast development and plant growth, thus increasing the biomass and yield. And the understanding of chloroplast gene expression regulation is helpful for exploring new ways to design the artificial photosynthesis and artificial chloroplast. Therefore, this research should also contribute to the improvement of agriculture and bioenergy industry.

光合作用是地球上物质循环与能量流动的最重要组成部分。叶绿体不仅是光合作用的主要场所，作为相对独立的转录翻译系统，它具有自己的基因组，及独特的调控方式—RNA编辑，但调控机制尚不清楚。前期工作构建并筛选了拟南芥突变体库；分离克隆到苗期致死SL1（Seedling Lethal 1）基因；初步验证了SL1蛋白的叶绿体定位及参与叶绿体基因表达调控的功能。基于以上研究基础，本项目将利用sl1突变体材料结合多种手段对SL1进行分析，明确其生物学功能，阐明其作用机理，进一步揭示SL1参与的调控途径，从而深入了解叶绿体基因表达调控的分子机制，及其对叶绿体发育的影响。此外，本项目的成果可结合生产实际，通过控制叶绿体基因表达，来促进植物叶绿体发育和植株生长，从而提高植物的生物量。同时，本项目的成果也将为光合作用及人工叶绿体的设计开拓潜在的新途径。因此本项目对农业和生物能源产业的发展也具有一定的理论指导作用。

通过筛选拟南芥T-DNA插入突变体库，我们发现了一个苗期致死、叶片白化的突变体，将其命名为sl1（seedling lethal 1）。Tail-PCR分离克隆到的 SL1基因可以互补恢复sl1的突变表型。SL1基因主要在进行光合作用的绿色组织器官中表达，SL1蛋白定位在叶绿体的基质中。生物信息学分析显示SL1蛋白含有MTERF结构域，属于线粒体转录终止因子mTERF（mitochondrial transcription termination factor）家族。这个家族广泛分布于多种真核生物中，在高等动物中，mTERF蛋白能调控线粒体基因的转录终止过程，而在植物中该家族的蛋白可能会参与叶绿体和线粒体基因组的转录或其他RNA代谢事件的调控。.在sl1突变体中，重要的叶绿体光合作用相关蛋白的表达量显著下降，且光系统复合体组装与叶绿体的发育均受到极大影响。我们对野生型和突变体的质体基因组RNA表达水平进行检测，发现突变体中多个质体基因表达量降低，而且质体基因组编码的RNA聚合酶 (PEP) 转录的质体基因表达量相较核基因组编码的RNA聚合酶 (NEP) 转录的质体基因下调程度更大。在对sl1突变体中RNA成熟加工过程的研究中，我们发现sl1突变体中部分质体基因在转录过程中的RNA剪接和RNA编辑相对于野生型存在缺失或效率降低。进一步研究发现SL1定位于叶绿体的拟核区域，且与PEP复合体中的多个蛋白存在相互作用。以上结果表明，SL1是拟南芥质体PEP转录复合体中的关键组分，对拟南芥质体基因组的转录过程及叶绿体的正常发育有着及其重要的作用。