Impacts des réarrangements génomiques chloroplastiques sur l'apparition des phénotypes de variégation chez Arabidopsis thaliana
In contrast to most non-photosynthetic eukaryotes, plants must ensure the stability of an additional genome contained within the plastid organelle. Despite the small size of the plastid genome and its low gene content, this genome is nevertheless absolutely essential for photosynthesis and plant energy metabolism. In spite of this, the main threats this genome encounters and their underlying consequences remain poorly understood. To evaluate the consequences of generalized plastid genome instability, we use the why1why3polIb Arabidopsis thaliana mutant line, which exhibits elevated levels of plastid genome rearrangements, and ciprofloxacin, a compound that induces double strand-breaks within organelle DNA. We demonstrated that high levels of plastid genome rearrangements lead to a decrease in photosynthetic electron transport chain efficiency and to a severe photosynthesis-associated oxidative stress. Surprisingly, these high levels of reactive oxygen species are neither associated to a loss of chloroplast function, nor to cell death. Instead, this redox imbalance seems to initiate a nuclear genetic expression remodelling that allows adaptation to this photosynthetic stress and confers tolerance to subsequent oxidative stresses. Using a novel approach for the analysis of next-generation sequencing data, we have also shown that a poorly characterized type of genomic instability constitutes one of the main threats to organelle genomic integrity, both in Arabidopsis and human. We demonstrate that this particular type of genomic instability, named U-turn-like DNA rearrangement, is most probably associated to errors during the replication process. Also, a genetic approach revealed that the chloroplast-localized proteins WHY1, WHY3 and RECA1 all act to repress this type of genomic instability, probably by stabilizing and stimulating the accurate restart of collapsed replication forks. A strong accumulation of U-turn-like rearrangements is notably associated to severe developmental defects in the why1why3reca1 mutant line. This raises the question of whether this type of genomic instability could be involved in the appearance of several mitochondria-associated pathologies.
ROS Whirly RecA plant biology chloroplast mitochondria genomic instability replication recombination