Maize EMP14 is required for mitochondrial RNA editing and intron splicing

Post-transcriptional modification of organellar RNA is critical for organellar gene expression, biogenesis, and function in plants. This process involves RNA splicing, editing, maturation, and stabilization. However, the underlying mechanism of these events is not fully understood. In this study, we report an E-type PPR protein EMP14 that is required for RNA editing and intron splicing in maize (Zea mays) mitochondria. Loss of EMP14 function arrested embryogenesis and endosperm development, leaving an empty pericarp phenotype in maize. Positional cloning identified that Emp14 encodes an E-subclass PPR protein localized to mitochondria. The emp14 mutants were impaired in the C-to-U editing at nad4-i3-2687, nad4-819, and ccmF_C-966 sites and the splicing of nad4 intron 3, resulting in substantially decreased nad4 transcript level and severely reduced assembly and activity of mitochondrial complex I. EMP14 interacts with PCW1 but not bCCP1 in the yeast two-hybrid assay and luciferase complementation imaging analysis, suggesting it recruits PCW1 as the trans deaminase but not facilitated by bCCP1. In vitro splicing assay showed that neither the edited nad4-i3-2687U nor the unedited nad4-i3-2687C could enable the splicing of nad4-i3. These results indicate that EMP14 is required for the C-to-U editing and intron splicing in mitochondria and is essential for seed development in maize.