The subject invention concerns materials and methods for providing plants or plant tissue with increased starch biosynthesis. Increased starch biosynthesis provides for increased yield. One aspect of the invention concerns polynucleotides that encode a mutant plant large subunit of AGPase. In one embodiment, a polynucleotide of the invention encodes a plant AGPase large subunit having an amino acid mutation wherein the cysteine amino acid corresponding to amino acid position 424 of wild type maize AGPase large subunit is substituted with an amino acid that results in increased AGPase activity when provided in an AGPase enzyme. In a specific embodiment, the cysteine corresponding to amino acid position 424 of wild type maize AGPase large subunit is substituted with a valine amino acid. The subject invention also comprises a mutant plant large subunit of AGPase encoded by a polynucleotide of the invention. Characterization of kinetic and allosteric properties indicates increased starch yield is provided when the polynucleotides of the invention are expressed in plants such as monocot endosperms.
