Systematic study of subcellular localization of Arabidopsis PPR proteins confirms a massive targeting to organelles

458 genes coding for PentatricoPeptide Repeat (PP R) proteins are annotated in the Arabidopsis thaliana genome. Over the past 10 years, numerous reports have shown that many of these proteins function in organelles to target specific transcripts and are involved in post-transcriptional regulation. Therefore, they are thought to be important players in the coordination between nuclear and organelle genome expression. Only four of these proteins have been described to be addressed outside organelles, indicating that some PP Rs could function in post-transcriptional regulations of nuclear genes. In this work, we updated and improved our current knowledge on the localization of PP R proteins of Arabidopsis within the plant cell. We particularly investigated the subcellular localization of 166 PP R proteins whose targeting predictions were ambiguous, using acombination of high-throughput cloning and microscopy. Through systematic localization experiments and data integration, we confirmed that PP R proteins are largely targeted to organelles and showed that dual targeting to both the mitochondria and plastid occurs more frequently than expected. These results allow us to speculate that dual-targetedPP R proteins could be important for the fine coordination of gene expressions in both organelles. © 2013 Landes Bioscience.