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Most of the reported P‐type pentatricopeptide repeat (PPR) proteins play roles in organelle RNA stabilization and splicing. However, P‐type PPRs involved in both RNA splicing and editing have rarely been reported, and their underlying mechanism remains largely unknown. Here, we report a rice floury endosperm22 (flo22) mutant with delayed amyloplast development in endosperm cells. Map‐based cloning and complementation tests demonstrated that FLO22 encodes a mitochondrion‐localized P‐type PPR protein. Mutation of FLO22 resulting in defective trans‐splicing of mitochondrial nad1 intron 1 and perhaps causing instability of mature transcripts affected assembly and activity of complex Ⅰ, and mitochondrial morphology and function. RNA‐seq analysis showed that expression levels of many genes involved in starch and sucrose metabolism were significantly down‐regulated in the flo22 mutant compared with the wild type, whereas genes related to oxidative phosphorylation and the tricarboxylic acid cycle were significantly up‐regulated. In addition to involvement in splicing as a P‐type PPR protein, we found that FLO22 interacted with DYW3, a DYW‐type PPR protein, and they may function synergistically in mitochondrial RNA editing. The present work indicated that FLO22 plays an important role in endosperm development and plant growth by participating in nad1 maturation and multi‐site editing of mitochondrial messager RNA. [ABSTRACT FROM AUTHOR]

Background: The sequences of several important mitochondrion-encoded genes involved in respiration in higher plants are interrupted by introns. Many nuclear-encoded factors are involved in splicing these introns, but the mechanisms underlying this splicing remain unknown. Results: We isolated and characterized a rice mutant named floury shrunken endosperm 5 (fse5). In addition to having floury shrunken endosperm, the fse5 seeds either failed to germinate or produced seedlings which grew slowly and died ultimately. Fse5 encodes a putative plant organelle RNA recognition (PORR) protein targeted to mitochondria. Mutation of Fse5 hindered the splicing of the first intron of nad4, which encodes an essential subunit of mitochondrial NADH dehydrogenase complex I. The assembly and NADH dehydrogenase activity of complex I were subsequently disrupted by this mutation, and the structure of the mitochondria was abnormal in the fse5 mutant. The FSE5 protein was shown to interact with mitochondrial intron splicing factor 68 (MISF68), which is also a splicing factor for nad4 intron 1 identified previously via yeast two-hybrid (Y2H) assays. Conclusion: Fse5 which encodes a PORR domain-containing protein, is essential for the splicing of nad4 intron 1, and loss of Fse5 function affects seed development and seedling growth. [ABSTRACT FROM AUTHOR]