OsPK2 encodes a plastidic pyruvate kinase involved in rice endosperm starch synthesis, compound granule formation and grain filling

Abstract

SummaryStarch is the main form of energy storage in higher plants. Although several enzymes and regulators of starch biosynthesis have been defined, the complete molecular machinery remains largely unknown. Screening for irregularities in endosperm formation in rice represents valuable prospect for studying starch synthesis pathway. Here, we identified a novel rice white‐core endosperm and defective grain filling mutant, ospk2, which displays significantly lower grain weight, decreased starch content and alteration of starch physicochemical properties when compared to wild‐type grains. The normal starch compound granules were drastically reduced and more single granules filled the endosperm cells of ospk2. Meanwhile, the germination rate of ospk2 seeds after 1‐year storage was observably reduced compared with wild‐type. Map‐based cloning of OsPK2 indicated that it encodes a pyruvate kinase (PK, ATP: pyruvate 2‐O‐phosphotransferase, EC 2.7.1.40), which catalyses an irreversible step of glycolysis. OsPK2 has a constitutive expression in rice and its protein localizes in chloroplasts. Enzyme assay showed that the protein product from expressed OsPK2 and the crude protein extracted from tissues of wild‐type exhibits strong PK activity; however, the mutant presented reduced protein activity. OsPK2 (PKpα1) and three other putative rice plastidic isozymes, PKpα2, PKpβ1 and PKpβ2, can interact to form heteromer. Moreover, the mutation leads to multiple metabolic disorders. Altogether, these results denote new insights into the role of OsPK2 in plant seed development, especially in starch synthesis, compound granules formation and grain filling, which would be useful for genetic improvement of high yield and rice grain quality.

Genetic Dissection of qPCG1 for a Quantitative Trait Locus for Percentage of Chalky Grain in Rice (Oryza sativa L.)

“…Thus we speculated that chalkiness was not a simple correlation but a complicated relationship with amylose content and further studies should be conducted about the relationship between chalkiness and amylose content. Unlike the inconclusive relationship between chalkiness and amylose content, high chalkiness was accompanied with short chains decrease and long chain increase of amylopectin in this study as same as previous studies ( Yamakawa et al, 2007 ; Lin et al, 2016 ; Cai et al, 2018 ). In Umemoto’s report, lower temperature led to an increased proportion of chains of DP 6–13 and decreased the percentage of chains with DP 20–27 and DP 44–54 and no statistically significant differences were observed in the proportions of each fraction of amylopectin between non-waxy and waxy varieties ( Umemoto et al, 1999 ).…”

Quantitative Proteomic Analysis of Alligator Weed Leaves Reveals That Cationic Peroxidase 1 Plays Vital Roles in the Potassium Deficiency Stress Response

“…Pyruvate kinase (PK) is a key enzyme in carbon metabolism and the glycolytic pathway. Previous studies showed that down-regulated expression of PK altered the growth of transgenic tobacco plants [20]; rice OsPK2 is involved in endosperm starch synthesis, compound granule formation, and grain filling [21]. In our study, PK2 was significantly up-regulated, suggesting changes in the carbohydrate metabolic process could be an important mechanism to cope with LK stress in plants [22].…”

Transcriptional and Biochemical Characterization of Cytosolic Pyruvate Kinases in Arabidopsis thaliana

“…An enhanced PK activity was accompanied by a reduced cytosolic pH, which was caused by H + -symport that affected the uptake of endosperm-derived sugars and amino acids. Protein degradation is another way of controlling PK activity as shown recently for cotton cytosolic pyruvate kinase 6 (GhPK6) [11]. Here phosphorylation-mediated ubiquitination of GhPK6 appears to modulate the cotton fiber elongation process.…”