Abstract
Starch, as a main energy storage substance, plays an important role in plant growth and human life. Despite the fact that several enzymes and regulators involved in starch biosynthesis have been identified, the regulating mechanism of starch synthesis is still unclear. In this study, we isolated a rice floury endosperm mutant M14 from a mutant pool induced by 60Co. Both total starch content and amylose content in M14 seeds significantly decreased, and starch thermal and pasting properties changed. Compound starch granules were defected in the floury endosperm of M14 seeds. Map-based cloning and a complementation test showed that the floury endosperm phenotype was determined by a gene of OsPPDKB, which encodes pyruvate orthophosphate dikinase (PPDK, EC 2.7.9.1). Subcellular localization analysis demonstrated that PPDK was localized in chloroplast and cytoplasm, the chOsPPDKB highly expressed in leaf and leaf sheath, and the cyOsPPDKB constitutively expressed with a high expression in developing endosperm. Moreover, the expression of starch synthesis-related genes was also obviously altered in M14 developing endosperm. The above results indicated that PPDK played an important role in starch metabolism and structure in rice endosperm.
Highlights
IntroductionMature seeds of cereals such as rice, maize and wheat contain large amounts of starch
In cereal endosperm, starch is synthesized in amyloplasts and forms starch granules
The M14 with a floury endosperm phenotype was identified from a 60Co-irradiated mutant pool of japonica rice variety Kitaake, and displayed no visible differences from wild type (WT) plants at the vegetative stage
Summary
Mature seeds of cereals such as rice, maize and wheat contain large amounts of starch. The mutations in the above starch synthesis key enzymes cause abnormal characteristics of endosperm starch with opaque-seed phenotype including shrunken, floury and white-core endosperm. The amylose-extender (ae) mutant lacking BEIIb produces a white-core endosperm and alters the fine structure of amylopectin [7]. FLO2 (FLOURY ENDOSPERM2), encoding a tetratricopeptide repeat motif-containing protein, affects the starch quality by regulating the expression of starch synthesis-related genes [8,9]. FLO6 contains a CBM48 domain in the C-terminal and regulates the starch synthesis and starch granule development by interacting with ISA1 [10]. Our data showed a vital importance of OsPPDKB in starch metabolism and structure in rice endosperm development
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