Summary Endosperm, the major storage organ in cereal grains, determines grain yield and quality. Despite the fact that a role for P‐type pentatricopeptide repeat (PPR) proteins in the regulation of endosperm development has emerged, molecular functions of many P‐type PPR proteins remain obscure. Here, we report a rice endosperm defective mutant, floury endosperm10 (flo10), which developed smaller starch grains in starchy endosperm and abnormal cells in the aleurone layer. Map‐based cloning and rescued experiments showed that FLO10 encodes a P‐type PPR protein with 26 PPR motifs, which is localized to mitochondria. Loss of function of FLO10 affected the trans‐splicing of the mitochondrial nad1 intron 1, which was accompanied by the increased accumulation of the nad1 exon 1 and exons 2–5 precursors. The failed formation of mature nad1 led to a dramatically decreased assembly and activity of complex I, reduced ATP production, and changed mitochondrial morphology. In addition, loss of function of FLO10 significantly induced an alternative respiratory pathway involving alternative oxidase. These results reveal that FLO10 plays an important role in the maintenance of mitochondrial function and endosperm development through its effect on the trans‐splicing of the mitochondrial nad1 intron 1 in rice.

Flowering time is an important trait for determining the adaptability of a crop cultivar. A novel heading date regulator, OsHAPL1, interacts with DTH8-Hd1 to negatively regulate flowering time in rice.

Proper chloroplast development and chlorophyll biosynthesis are essential for the photoautotrophic plants. The insertion of magnesium (Mg 2+ ) into protoporphyrin IX (Proto), catalyzed by magnesium chelatase (Mgchelatase), is the first committed step of chlorophyll biosynthesis. In dicot plants, a proposed model revealed that Mg-chelatase I subunit (CHLI) and Mg-chelatase D subunit (CHLD) can interact directly; however, their relation remains elusive in rice, a monocot model plant. In this study, we characterized a chlorophyll-deficiency mutant, etiolated leaf and lethal (ell), which displayed a yellow leaf in young seedlings and became lethal after three-leaf stage. Chlorophyll content in homozygous ell mutant was approximately 1 % of that in the wild type. Besides, chloroplast development in the mutant was entirely arrested and no thylakoid structure was observed. By map-based cloning, the ell locus was delimited to a 3.9-Mb interval in chromosome 3. A single-base mutation (G529C) inOsCHLI was identified, leading to an amino acid substitution (G177R) in a highly conserved region. Compared with the wild type, more Proto but less magnesium protoporphyrin IX (Mg-Proto) was measured in the ell mutant. Using protoplast transfection and callus transformation, we found that exogenous OsCHLI could consistently recover the lesion of chloroplast in the ell mutant. By subcellar localization analysis, OsCHLI was detected in the chloroplast. Despite the secondary structure of OsCHLI that was predicted to be altered in the mutant, the point mutation did not affect subcellular localization. Real-time PCR demonstrated that the ell mutation induced significantly transcriptional downregulation of the photosynthesis-associated nuclear and plastid genes. Additionally, yeast-two-hybrid experiments indicated that the single amino acid substitution blocked the intrinsic interaction between OsCHLI and OsCHLD. Moreover, OsCHLI showed physical interactions with some thioredoxins (TRXs), suggesting a similar regulatory mechanism of Mg-chelatase activity in both monocot and dicot plants. Keywords Rice . Map-based cloning . Mg-chelatase . OsCHLI subunit . OsCHLD subunit . Thioredoxin Abbreviations Proto Protoporphyrin IX Mg-chelatase Magnesium chelatase ell Etiolated leaf and lethal Mg-Proto Magnesium protoporphyrin IX TRX Thioredoxin EMS Ethyl methyl sulfonate CHLH Mg-chelatase H subunit Electronic supplementary material The online version of this article (

Summary Rice (Oryza sativa) is a facultative short‐day (SD) plant, flowering early under SD and late under long‐day (LD) conditions. Ghd7 is a major regulator of flowering time in rice, which strongly delays flowering under LD. Induction of Ghd7 expression by phytochromes has been shown to contribute to photoperiodic regulation of flowering in rice. Here, we show that Ghd7 also is regulated by phytochromes at a post‐transcriptional level. We found that constitutive expression of Ghd7 delays flowering in the wild‐type (WT) background, but not in the se5 mutant background (deficient in functional phytochromes) under LD and that Ghd7 protein fails to accumulate in the se5 mutant. We also found that co‐expressing OsGIGANTEA (OsGI) with Ghd7 causes reduced accumulation of Ghd7 protein and partially suppresses the delayed flowering phenotype in the WT background, suggesting that phytochromes and OsGI play antagonist roles in regulating Ghd7 protein stability and flowering time. We show that OsPHYA, OsPHYB and OsGI could directly interact with Ghd7. Interestingly, OsPHYA and OsPHYB could inhibit the interaction between OsGI and Ghd7, thus helping to stabilize Ghd7 protein. Our results revealed a new level of Ghd7 regulation by phytochromes and OsGI in photoperiodic control of flowering in rice.

Rice production and seed storage are confronted with grain deterioration and loss of seed viability. Some members of the lipoxygenase (LOX) family function in degradation of storage lipids during the seed germination, but little is known about their influence on seed longevity during storage. We characterized the role of rice OsLOX2 gene in seed germination and longevity via over-expression and knock-down approaches. Abundant expression of OsLOX2 was detected in panicles, roots, and stems, but not in leaves. Moreover, OsLOX2 was highly induced during germination. OsLOX2 protein, located in the cytoplasm, showed a wide range of temperature adaptation (20-50 °C) and a substrate preference to linoleic acid. Lines over-expressing OsLOX2 showed accelerated seed germination under normal condition and lower seed viability after accelerated aging. RNA interference (RNAi) of OsLOX2 caused delayed germination and enhanced seed longevity. RNAi lines with strongly repressed OsLOX2 activity completely lost the capability of germination after accelerated aging. More lipid hydroperoxide were found in OE15 than the control, but less in RNAi lines than in the WT Nipponbare. Therefore, OsLOX2 acts in opposite directions during seed germination and longevity during storage. Appropriate repression of the OsLOX2 gene may delay the aging process during the storage without compromising germination under normal conditions.

Heading date is an important agronomic trait affecting crop yield. The GRAS protein family is a plant-specific super family extensively involved in plant growth and signal transduction. However, GRAS proteins are rarely reported have a role in regulating rice heading date. Here, we report a GRAS protein DHD1 (Delayed Heading Date1) delays heading and enhances yield in rice. Biochemical assays showed DHD1 physically interacts with OsHAP5C/D both in vitro and in vivo. DHD1 and OsHAP5C/D located in the nucleus and showed that rhythmic expression. Both DHD1 and OsHAP5C/D affect heading date by regulating expression of Ehd1. We propose that DHD1 interacts with OsHAP5C/D to delay heading date by inhibiting expression of Ehd1.

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