Title : Editing of mitochondrial transcripts nad 3 and cox 2 by Dek 10 is 1 essential for mitochondrial function and maize plant development

55 Respiration, the core of mitochondrial metabolism, depends on the function of 56 five respiratory complexes. Many respiratory chain related proteins are 57 encoded by the mitochondrial genome and their RNAs undergo 58 post-transcriptional modifications by nuclear genome expressed factors, 59 including pentatricopeptide repeat (PPR) proteins. Maize defective kernel 10 60 (dek10) is a classic mutant with small kernels and delayed development. 61 Through positional cloning we found that Dek10 encodes an E-subgroup PPR 62 protein localized in mitochondria. Sequencing analysis indicated that Dek10 is 63 responsible for the C-to-U editing at nad3-61, nad3-62, and cox2-550 sites, 64 those are specific editing sites in monocots. The defects of these editing sites 65 result in significant reduction of Nad3 and the loss of Cox2. Interestingly, the 66 assembly of Complex I was not reduced, but its NADH dehydrogenase activity 67 was greatly decreased. The assembly of Complex IV was significantly reduced. 68 Transcriptome and transmission electron microscopy (TEM) analysis revealed 69 that proper editing of nad3 and cox2 is critical for mitochondrial functions, 70 biogenesis and morphology. These results indicate that the E-subgroup PPR 71 protein Dek10 is responsible for multiple editing sites in nad3 and cox2, that is 72 essential for mitochondrial functions and plant development in maize. 73