Genetic Dissection of the Morphological Evolution of Maize

Abstract

Maize (Zea mays ssp. mays) and its wild progenitor, teosinte (Z. mays ssp. parviglumis) differ dramatically in inflorescence and plant architecture despite the fact that their evolutionary divergence occurred within the past 10,000 years or less. To elucidate the genetic control of the morphological differences between maize and teosinte, my colleague and I employed quantitative trait locus mapping with molecular markers. Results indicated that most of the variation in plant and inflorescence morphology between maize and teosinte can be explained by five restricted regions of the genome. In this paper, characterization of three of these regions and their effects on plant and inflorescence development will be discussed. Each of these regions appears to contain a single major locus of large effect. One of these loci, teosinte branched1, largely controls the difference in plant architecture. Another, teosinte glume architecture1, controls the formation of the teosinte cupulate fruitcase that encases the kernel. A third candidate, terminal ear1, is hypothesized to control internode elongation within the inflorescence. In addition to their main effects, each locus appears to have pleiotropic effects on other traits. Genetic analyses also demonstrate that some of these loci exhibit epistatic interactions. The results suggest that mutations at a small number (five) of regulatory loci may have been the initial steps in the domestication of maize, supporting a model for maize evolution proposed by George Beadle in 1939.