This protein plays a role in synthesis of starch. It catalyzes the synthesis of the activated glycosyl donor, ADP-glucose from Glc-1-P and ATP. alpha-D-glucose 1-phosphate + ATP + H(+) = ADP-alpha-D-glucose + diphosphate Insensitive to 3'phosphoglycerate and orthophosphate. Glycan biosynthesis; starch biosynthesis. Heterotetramer. Found in the chloroplast in leaf. Found in the plastid in the developing endosperm. Abundantly expressed in the whole grains, a slightly less abundant expression is seen in leaves, while a low level expression is seen in the roots. A greater expression is seen in the endosperm than in the embryo and pericarp layers. Is expressed prior to 10 dpa (days post anthesis), accumulates to the highest levels between 20 and 35 dpa and levels decrease after 35 dpa. Belongs to the bacterial/plant glucose-1-phosphate adenylyltransferase family.