Participates in sensing carbon and organic nitrogen status and regulates some steps of primary carbon and nitrogen metabolism. Required for nitrite uptake in chloroplasts and regulates arginine biosynthesis through interaction with acetylglutamate kinase (NAGK) in chloroplasts. Regulates fatty acids synthesis in chloroplasts by interacting with the acetyl-CoA carboxylase complex and inhibiting acetyl-CoA carboxylase (ACCase) activity. Homodimer. Interacts with NAGK. Interaction with NAGK is dependent of MgATP and inhibited by 2-oxoglutarate, arginine, glutamate, citrate, and oxaloacetate. By light and sucrose. Down-regulated by treatment with amino acids. No visible phenotype under normal growth condition, but increased sensitivity to elevated levels of nitrite. Belongs to the P(II) protein family.