OsPHO1;2 exports excess Pi from endosperm to maintain proper levels of AGPase activity for starch biosynthesis
During starch biosynthesis in developing endosperm, glucose-1-P and ATP are converted into ADP-glucose and inorganic pyrophosphate (PPi) by ADP-glucose pyrophosphorylase (AGPase). ADP-glucose is used for starch biosynthesis and PPi is hydrolyzed into Pi. The plasma membrane (PM)-localized OsPHO1;2 is expressed in the endosperm cells and exports excess Pi from the developing endosperm to maintain Pi homeostasis for proper levels of AGPase activity and starch biosynthesis. In the Ospho1;2 mutants, Pi accumulates in endosperm cells, which represses AGPase activity and consequently inhibits starch biosynthesis.