Maintenance of plastid genome stability in plants

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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.