Pyrophosphate‐fructose 6‐phosphate 1‐phosphotransferase ( PFP 1) regulates starch biosynthesis and seed development via heterotetramer formation in rice ( Oryza sativa L.)

Summary Pyrophosphate‐fructose 6‐phosphate 1‐phosphotransferase ( PFP 1) reversibly converts fructose 6‐phosphate and pyrophosphate to fructose 1, 6‐bisphosphate and orthophosphate during glycolysis, and has diverse functions in plants. However, mechanisms underlying the regulation of starch metabolism by PFP 1 remain elusive. This study addressed the function of PFP 1 in rice floury endosperm and defective grain filling. Compared with the wild type, pfp1‐3 exhibited remarkably low grain weight and starch content, significantly increased protein and lipid content, and altered starch physicochemical properties and changes in embryo development. Map‐based cloning revealed that pfp1‐3 is a novel allele and encodes the regulatory β‐subunit of PFP 1 ( PFP 1β). Measurement of nicotinamide adenine dinucleotide ( NAD +) showed that mutation of PFP 1β markedly decreased its enzyme activity. PFP 1β and three of four putative catalytic α‐subunits of PFP 1, PFP 1α1, PFP 1α2, and PFP 1α4, interacted with each other to form a heterotetramer. Additionally, PFP 1β, PFP 1α1 and PFP 1α2 also formed homodimers. Furthermore, transcriptome analysis revealed that mutation of PFP 1β significantly altered expression of many essential enzymes in starch biosynthesis pathways. Concentrations of multiple lipid and glycolytic intermediates and trehalose metabolites were elevated in pfp1‐3 endosperm, indicating that PFP 1 modulates endosperm metabolism, potentially through reversible adjustments to metabolic fluxes. Taken together, these findings provide new insights into seed endosperm development and starch biosynthesis and will help in the breeding of rice cultivars with higher grain yield and quality.