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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]

Summary: Starch accounts for over 80% of the total dry weight in cereal endosperm and determines the kernel texture and nutritional quality. Amyloplasts, terminally differentiated plastids, are responsible for starch biosynthesis and storage. We screened a series of rice mutants with floury endosperm to clarify the mechanism underlying amyloplast development and starch synthesis. We identified the floury endosperm19 (flo19) mutant which shows opaque of the interior endosperm. Abnormal compound starch grains (SGs) were present in the endosperm cells of the mutant. Molecular cloning revealed that the FLO19 allele encodes a plastid‐localized pyruvate dehydrogenase complex E1 component subunit α1 (ptPDC‐E1‐α1) that is expressed in all rice tissues. In vivo enzyme assays demonstrated that the flo19 mutant showed decreased activity of the plastidic pyruvate dehydrogenase complex. In addition, the amounts of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) were much lower in the developing flo19 mutant endosperm, suggesting that FLO19 participates in fatty acid supply for galactolipid biosynthesis in amyloplasts. FLO19 overexpression significantly increased seed size and weight, but did not affect other important agronomic traits, such as panicle length, tiller number and seed setting rate. An analysis of single nucleotide polymorphism data from a panel of rice accessions identified that the pFLO19L haplotype was positively associated with grain length, implying a potential application in rice breeding. In summary, our study demonstrates that FLO19 is involved in galactolipid biosynthesis which is essential for amyloplast development and starch biosynthesis in rice. [ABSTRACT FROM AUTHOR]

Summary: Thioredoxins (TRXs) occur in plant chloroplasts as complex disulphide oxidoreductases. Although many biological processes are regulated by thioredoxins, the regulatory mechanism of chloroplast TRXs are largely unknown.Here we report a rice white panicle2 mutant caused by a mutation in the thioredoxin z gene, an orthologue of AtTRX z in Arabidopsis. white panicle2 (wp2) seedlings exhibited a high‐temperature‐sensitive albinic phenotype.We found that plastid multiple organellar RNA editing factors (MORFs) were the regulatory targets of thioredoxin z. We showed that OsTRX z protein physically interacts with OsMORFs in a redox‐dependent manner and that the redox state of a conserved cysteine in the MORF box is essential for MORF–MORF interactions. wp2 and OsTRX z knockout lines show reduced editing efficiencies in many plastidial‐encoded genes especially under high‐temperature conditions. An Arabidopsis trx z mutant also exhibited significantly reduced chloroplast RNA editing.Our combined results suggest that thioredoxin z regulates chloroplast RNA editing in plants by controlling the redox state of MORFs. [ABSTRACT FROM AUTHOR]