Compositions and methods for modulating MIOX activity are provided. Such compositions include nucleotide sequences for novel MIOX sequences obtained from maize, amino acid sequences for the proteins encoded by the nucleotide sequences of the invention, and variants and fragments thereof. Methods of the invention involve introducing into a plant a nucleotide construct comprising a MIOX nucleotide sequence operably linked to a promoter that drives expression in a plant. Expression of the novel nucleotide sequences disclosed herein confers advantageous agronomic properties on a plant. Transformed plants, plant cells, and seeds are additionally provided.