Maintenance of plastid genome stability in plants

光合作用是地球上最重要的生物过程之一。我们所有的食物以及我们对纤维和建筑材料的大部分需求都是由这一过程直接或间接提供的。光合作用发生在叶绿体中，并依赖于位于细胞器和细胞核中的一组基因。存在于叶绿体中的基因是质体基因组的一部分，编码参与光合作用、基因转录和蛋白质合成的RNA和蛋白质。尽管这种基因组对植物和一般生命至关重要，但我们对它的转录、复制和DNA修复机制仍然知之甚少。近年来，我的实验室研究了植物特异性dna结合蛋白的一个小家族，称为Whirly，以及一种特殊的i型聚合酶PolIB，它们参与了质体基因组稳定性的维持。

Photosynthesis is one of the most important biological processes on earth. All our food and a large part of our needs for fibre and building materials are provided by this process, either directly or indirectly. Photosynthesis occurs in the chloroplast, and depends on a subset of genes that are located in this organelle and in the nucleus. The genes present in the chloroplast are part of the plastid genome and encode for RNA and proteins involved in photosynthesis, gene transcription and protein synthesis. Despite the crucial importance of this genome for plants and life in general, we still know very little about its transcription, replication and DNA repair mechanisms. In recent years my laboratory has characterized a small family of plant specific DNA-binding proteins, called Whirly, as well as a specialized type-I polymerase, PolIB, that are involved in the maintenance of plastid genome stability. In the next granting period we propose to continue our characterization of the mechanisms that contribute to maintain the stability of the plastid genome. We will focus our attention mostly on a few genes whose mutation leads to hypersensitivity to the organelle-specific DNA double-stranded breaks inducing agent ciprofloxacin. These genes code for the WHY1 and WHY3 proteins, the plastid Sigma factor SIG6, the recombinase RecA1, the PolIB DNA polymerase and the RecG functional homolog DRT111. We will determine the genetic interactions between these genes, which should provide important clues to understand the mechanisms that maintain plastid genome stability. As preliminary results indicate that the transcription regulator SIG6 acts as an important mediator of genome stability, we will test the hypothesis that transcription has a strong genome destabilization effect in plastids at an early stage of development and that Whirly proteins contribute to counteract this effect.