Growing Slowly 1 locus encodes a PLS-type PPR protein required for RNA editing and plant development in Arabidopsis

Most pentatricopeptide repeat (PPR) proteins are involved in organelle post-transcriptional processes, including RNA editing. The PPR proteins include the PLS subfamily, containing characteristic triplets of P, L, and S motifs; however, their editing mechanisms and roles in developmental processes are not fully understood. In this study, we isolated the Arabidopsis thaliana Growing slowly 1 (AtGRS1) gene and showed that it functions in RNA editing and plant development. Arabidopsis null mutants of grs1 exhibit slow growth and sterility. Further analysis showed that cell division activity was reduced dramatically in the roots of grs1 plants. We determined that GRS1 is a nuclear-encoded mitochondria-localized PPR protein, and is a member of the PLS subfamily. GRS1 is responsible for the RNA editing at four specific sites of four mitochondrial mRNAs: nad1-265, nad4L-55, nad6-103, and rps4-377. The first three of these mRNAs encode for the subunits of complex I of the electron transport chain in mitochondria. Thus, the activity of complex I is strongly reduced in grs1. Changes in RPS4 editing in grs1 plants affect mitochondrial ribosome biogenesis. Expression of the alternative respiratory pathway and the abscisic acid response gene ABI5 were up-regulated in grs1 mutant plants. Genetic analysis revealed that ABI5 is involved in the short root phenotype of grs1. Taken together, our results indicate that AtGRS1 regulates plant development by controlling RNA editing in Arabidopsis.