Abstract
Key messageDecreased PFPase activity in rice perturbs the equilibration of carbon metabolism during grain filling but has no visible phenotypic effects during the vegetative and reproductive growth stages.Starch is a primary energy reserve for various metabolic processes in plant. Despite much advance has been achieved in pathways involved in starch biosynthesis, information was still lacked for precise regulation related to carbon metabolism during seed filling in rice (Oryza sativa). The objective of this study was to identify and characterize new gene associated with carbon metabolism during grain filling. By screening our chemical mutant pool, two allelic mutants exhibiting floury endosperm were isolated. No visible phenotypic defects were observed during both the vegetative and reproductive growth stages, except for the floury-like endosperm of grains with significantly reduced kernel thickness, 1000-grain weight and total starch content. Map-based cloning revealed that the mutant phenotypes were controlled by a gene encoding pyrophosphate: fructose-6-phosphate 1-phosphotransferase (PFP, EC 2.7.1.90) β subunit (PFPβ), which catalyzes reversible interconversion between fructose-6-phosphate and fructose-1, 6-bisphosphate. The identity of PFPβ was further confirmed by a genetic complementation test. Subcellular analysis demonstrated that PFPβ was localized in cytoplasm. Quantitative PCR and histochemical staining indicated PFPβ was ubiquitously expressed in various tissues. Furthermore, we found PFPβ could express in both the early and late phases of starch accumulation during grain filling and decreased activity of PFPβ in pfp mutants resulted in compromised carbon metabolism with increased soluble sugar contents and unfavorable starch biosynthesis. Our results highlight PFPβ functions in modulating carbon metabolism during grain filling stage.Electronic supplementary materialThe online version of this article (doi:10.1007/s00299-016-1964-4) contains supplementary material, which is available to authorized users.
Highlights
Starch is the primary storage polysaccharide in many sink tissues in plants, such as potato (Solanum tuberosum) tubers and rice (Oryza sativa) and maize (Zea mays) seeds, and serves as an energy reserve for various metabolic processes
Despite much advance has been achieved in pathways involved in starch biosynthesis, information was still lacked for precise regulation related to carbon metabolism during seed filling in rice (Oryza sativa)
We found PFPb could express in both the early and late phases of starch accumulation during grain filling and decreased activity of PFPb in pfp mutants resulted in compromised carbon metabolism with increased soluble sugar contents and unfavorable starch biosynthesis
Summary
Starch is the primary storage polysaccharide in many sink tissues in plants, such as potato (Solanum tuberosum) tubers and rice (Oryza sativa) and maize (Zea mays) seeds, and serves as an energy reserve for various metabolic processes. Starch biosynthesis in the endosperm of cereals such as rice requires a concerted series of enzymatic reactions involving ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SS), granule-bound starch synthase (GBSS), starch branching enzyme (BE), starch debranching enzyme (DBE), phosphorylase (PHO) and disproportionating enzyme (DPE). Mutants defective in these enzymes exhibit abnormal features of endosperm starch with opaque-kernel phenotypes, which were variously described as floury, glutinous, shrunken, dull, white-belly and white-core grains somewhere (Nelson and Pan 1995). As a result, these mutants provide valuable genetic materials for elucidation of metabolic processes related to nutrient storage during grain filling (Nelson and Pan 1995). FLO6, encoding a CBM48 domain-containing protein, is involved in compound granule formation and starch synthesis via direct interaction with isoamylase 1 (ISA1) in developing rice seeds (Peng et al 2014)
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