Embryo rescue uncovers an essential role for MEF45 in four mitochondrial RNA editing events in Arabidopsis

C-to-U RNA editing is an important post-transcriptional regulatory process required for proper gene expression in plant organelles.To date, over a hundred PLS-type Pentatricopeptide repeat (PPR) proteins have been characterized as site-specific RNA editing factors, largely through genetic analyses of their mutant lines.However, disruption of RNA editing factors often causes severe defects in mitochondrial and chloroplast function, frequently resulting in arrested embryogenesis, which hampers detailed molecular and phenotypic analyses.To overcome this limitation, several strategies have been developed to obtain sufficient plant material for functional studies.Here, we report a novel E2-subclass PPR protein whose homozygous insertion mutant fails to develop mature embryos.Immature embryos of T-DNA mutants of Mitochondrial RNA Editing Factor 45 (MEF45) were rescued in vitro on agar medium supplemented with vitamins and a high concentration of sucrose, and successfully developed into slow-growing plantlets.Analysis of the rescued mef45 mutant revealed a complete loss of RNA editing at four mitochondrial sites, cob-1084, ccmC-608, nad5-1490, and matR-1596.These results indicate that embryo rescue is a powerful approach for analyzing essential genes involved in gene expression in plant mitochondria.