Rice Floury Shrunken Endosperm5 encodes a putative plant organelle RNA recognition protein that is required for cis-splicing of mitochondrial nad4 intron 1

Abstract Background: Some important mitochondrial-encoded genes for respiration in higher plants are interrupted by introns. Many nuclear-encoded factors are involved in the splicing of these introns, but the underlying mechanisms remain to be deciphered.Results: Here, we isolated and characterized a rice mutant named floury shrunken endosperm5 (fse5). In addition to floury shrunken endosperm seeds with mutant phenotype either failed to germinate or produced retarded lethal seedlings. The Fse5 encodes a putative plant organelle RNA recognition (PORR) protein targeted to mitochondria. Mutation of Fse5 hindered splicing of the first intron of nad4, that encodes an essential subunit of mitochondrial NADH dehydrogenase Complex I. The assembly and NADH dehydrogenase activity of Complex I were disrupted and the structure of the mitochondria was abnormal in the fse5 mutant. 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 in a yeast two-hybrid assay.Conclusion: Fse5 encoding a PORR protein is essential for splicing of nad4 intron 1, and loss of function affects seed development and seedling growth.