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Michael D. McMullen, Research Geneticist, was presented the Class of 2004 T. W. Edminster Research Associate Award for his proposal "Do ???signatures of selection" systematically identify key genes controlling agronomic traits?" on January 22, 2004 in New Orleans, LA during the annual ARS Recognition Program. The research is part of National Program 302???Plant Biological and Molecular Processes.

Mike???s Research Problem statement follows:

"One major bottleneck in using transformation technology for crop improvement is our lack of understanding of which genes control agronomic traits. In collaboration with John Doebley (University of Wisconsin) and Brandon Gaut (University of California, Irvine), we have developed a novel approach for identifying these key genes. Our approach is to contrast the genetic diversity remaining in genes in inbred lines of maize (improved maize) to the diversity present in accessions of the wild relative teosinte and exotic maize landraces. We initially demonstrated the validity of this approach using simple-sequence-repeat diversity within genes (Vigouroux et al., 2002. Proc. Natl. Acad. Sci. USA 99:9650 9655). We have since generalized the approach using DNA sequence diversity. The average (unselected) gene in maize retains approximately 60% of the sequence diversity in a diverse set of inbred lines compared to the teosinte accessions. However, a subset of genes (1-3%) retains essentially no sequence variation in the inbreds, but has normal levels in the teosinte accessions. Our explanation is that these genes exhibit a "signature of selection" in which specific alleles were selected during the domestication of maize by Native Americans or improvement by maize breeders. Our hypothesis is these genes were selected because they affected selected agronomic traits. Paradoxically, the genes that have undergone the greatest selection, that is reduction in diversity, have the least genetic variation remaining and therefore can not be further improved by standard plant breeding or identified by quantitative trait locus analysis because all inbred lines have identical alleles. Among the ???selected??? genes we have identified to date are transcription factors implicated in plant growth form and response to plant hormones, and a key enzyme in nitrogen and sulfur regulation. The objective of this Research Associate position will be to demonstrate that altering the expression of these genes modifies agronomic traits."


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Last Modified: 8/13/2016
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