Defective Kernel 6 encodes a PPR protein required for seed development in maize Running title : Dek 6 is required for seed development

RNA editing is a posttranscriptional process that is important in mitochondria and plastids of higher plants. All RNA editing specific trans-factors reported so far belong to PLS-class of pentatricopeptide repeat (PPR) proteins. Here, we report the map-based cloning and molecular characterization of a defective kernel mutant dek6 in maize. Loss of Dek6 function leads to delayed embryogenesis and endosperm development, reduced kernel size, and seedling lethality. Dek6 encodes an E sub-class PPR protein that targets to both mitochondria and chloroplasts, and is involved in RNA editing in mitochondrial NADH dehydrogenase3 (nad3) at nad3-247 and nad3-275. C to U editing of nad3-275 is not conserved and even lost in Arabidopsis, consisting with the idea that no close DEK6 homologs present in Arabidopsis. However, the amino acids generated by editing nad3-247 and nad3-275 are highly conserved in many other plant species, and the reductions of editing at these two sites decreased the activity of mitochondria NADH dehydrogenase complex I, indicating that the alteration of amino acid sequence is necessary for Nad3 function. Our results indicate that Dek6 encodes an E sub-class PPR protein that is involved in RNA editing of multiple sites and is necessary for seed development of maize.