EMB2217 Is a Mitochondrial PPR-SMR Protein Required for the Splicing of Multiple Group II Introns During Arabidopsis...

Pentatricopeptide repeat (PPR) proteins are key regulators of the organellar RNA metabolism in plants. However, the functions of mitochondrial PPR proteins belonging to the subclass of P-type PPR factors containing the SMR domain remain much less understood. Here, we characterize the EMBRYO DEFECTIVE 2217 (EMB2217/At1g79490), an essential PPR-SMR factor in Arabidopsis thaliana. T-DNA insertional lines at the AT1G79490 gene-locus exhibit embryonic arrest at the late heart stage and display defective germination and seedling establishment. Partial complementation using an ABI3 promoter-driven strategy enables efficient germination and the rescue of homozygous emb2217 plantlets. The pABI3::EMB2217 emb2217 -/- seedlings display severe growth defects due to impaired mitochondrial function, tightly associated with impaired OXPHOS activity. Analyses of mitochondrial RNA profiles reveal that EMB2217 is required for the processing of multiple group II introns that reside in the coding regions of several complex I (CI) subunits, the cox2 subunit of CIV, and the ribosomal rps3 factors. Our data further show that RNA maturation defects induce alternative electron transport and stress-response pathways, which are associated with developmental defects and modulation of photosynthetic and cellular metabolic processes. Together, we identify EMB2217 as a general mitochondrial splicing factor whose loss compromises OXPHOS biogenesis and function, cellular energy supply, and plant development.