Functional Analysis Of A Key Gene PPR536 In Maize Seed Development

Many genes are involved in the genetic regulation of seed development process from double fertilization to seed maturation.Hence,this study answers the fundamental question in plants by revealing the regulation mechanism in seed development,providing theoretical support for molecular breeding and crop yield.Pentatricopeptide repeat Proteins(PPRs)are widespread in eukaryotes,which play an essential role in the development of embryo.PPR proteins are composed of 2-30 tetratricopeptide repeat motifs,which contain 35 amino acid residues.The PPR proteins are classified into two subfamilies(P and PLS).The P type PPRs are mainly involved in RNA stabilization,RNA cleavage and RNA splicing,while the PLS type PPRs works during RNA editing.Most of PPRs are localized in mitochondrian or chloroplasts,playing an important role in post-transcriptional processing,cytoplasmic male sterility,embryogenesis and endosperm development in maize.Group II intron could be spliced by itself as a ribozyme.However,the organelle group II introns lost the self-splicing function,which was accomplished by the nuclear encoded proteins,such as P-type PPRs.Maize seeds were selected as the material in this study.The embryonic lethal mutation often leads to low yields,but the large kernel of maize gave us the opportunity to research the mechanisms of seed development.In this study,we obtained a maize mutant containing a defect P-type PPR named ppr536 from UniformMu seed library.The mutation of PPR53 6 leads to the developmental arrestation of both embryo and endosperm.The homogenous ppr536 kernel shows a typical empty pericarp phenotype,displaying the smaller,pale,shrunken kernel phenotypes,and could not germinate.We found that PPR536 is targeted to mitochondria,and that the splicing of mitochondrial nad1 intron4,nad4 intron 1-3,nad5 intron 1 and nad7 intron 3 are abolished in ppr536 mutant,causing the severely reduced assembly and activity of complex I and seed development in maize.In addition,the alternative respiratory pathway was induced in the ppr536 mutant.These results imply that PPR536 is special for nad1,nad4,nad5 and nad7 intron splicing,and crucial for complex I assembly,embryogenesis and seed development in maize.Therefore,the seed development is a complicated process,this study is not only working on the mechanisms of mitochondrial RNA splicing and the molecular regulation of maize seed development,but also supporting the molecular breeding in maize.