A RESTORER OF FERTILITY-like PPR Gene is Required for 5'-end Processing of the Nad4 MRNA in Mitochondria of Arabidopsis Thaliana

Processing of 5'-ends is a frequently observed step during maturation of plant mitochondrial mRNAs. Up to now, very little is known about the biochemistry of this process and the proteins involved in the removal of 5' leader sequences. Based on natural genetic variation we have used linkage mapping and complementation studies to identify a nuclear gene required for the efficient generation of a 5'-end 228 nucleotides upstream of the mitochondrial nad4 gene encoding subunit 4 of the NADH dehydrogenase complex. This nuclear gene, At1g12700, that we designate RNA PROCESSING FACTOR 1 (RPF1), encodes a pentatricopeptide repeat (PPR) protein of the P-class containing canonical PPR-repeats. RPF1 belongs to a subgroup of PPR proteins, which includes the RESTORER OF FERTILITY (RF) gene products restoring cytoplasmic male sterility (CMS) in various plant species. CMS is a mitochondrially inherited trait caused by the expression of aberrant, chimeric genes, which has not been observed in the predominantly inbreeding species Arabidopsis thaliana. The here reported results are a further step towards the characterization of the plant mitochondrial RNA processing machinery and provide additional insights into the function of RF-like PPR proteins.