Developmental analysis of teosinte glume architecture1: A key locus in the evolution of maize (Poaceae).

A key event in the evolution of maize from teosinte was a reduction in the cupulate fruitcase and softening of the glumes, which increased the accessibility of kernels for harvest. The teosinte glume architecture1 (tga1) locus largely controls this difference between maize and teosinte, and thus may have played a pivotal role in maize evolution. The teosinte allele (tga1+teosinte) lengthens inflorescence internodes, shortens rachillae, and makes glumes longer, thicker, and harder. Developmental characterization of morphometric traits reveals that differences among genotypes are apparent early in female inflorescence development. Increased hardening in glumes homozygous for tga1+teosinte is correlated with a thicker abaxial mesoderm of lignified cells. Silica deposition in the abaxial epidermal cells of the glumes is also affected. In the maize background, glumes homozygous for tga1+teosinte deposit silica in both the short and long cells of the glume epidermis, whereas glumes homozygous for the maize allele (Tga1+Maize) concentrate silica only in the short cells. Silica deposition also appears to be affected by genetic background. The effects of tga1 appear largely to explain the differences in glume induration between maize and teosinte. The diverse pleiotropic effects of tga1 suggest that it is regulatory in nature.