In higher plants, chloroplast and mitochondrial transcripts contain a number of group II introns that need to be precisely spliced before translation into functional proteins. However, the mechanism of splicing and the factors involved in this process are not well understood. By analysing a seed mutant in maize, we report here the identification ofEmpty pericarp16(Emp16) that is required for splicing ofnad2intron 4 in mitochondria. Disruption ofEmp16function causes developmental arrest in the embryo and endosperm, giving rise to an empty pericarp phenotype in maize. Differentiation of the basal endosperm transfer layer cells is severely affected. Molecular cloning indicates thatEmp16encodes a P-type pentatricopeptide repeat (PPR) protein with 11 PPR motifs and is localized in the mitochondrion. Transcript analysis revealed that mitochondrialnad2intron 4 splicing is abolished in theemp16mutants, leading to severely reduced assembly and activity of complex I. In response, the mutant dramatically increases the accumulation of mitochondrial complex III and the expression of alternative oxidaseAOX2. These results imply that EMP16 is specifically required for mitochondrialnad2intron 4cis-splicing and is essential for complex I assembly and embryogenesis and development endosperm in maize.Significance Statement
Pentatricopeptide repeat (PPR) proteins are required for RNA splicing, editing, stability, maturation, and translation of mitochondrial and chloroplast transcripts. Here we show that lack of a P-type PPR protein accounts for the embryo lethality of the maize empty pericarp16 mutant.