Submitted to: Maydica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2009
Publication Date: 12/1/2009
Citation: Flint Garcia, S.A., Guill, K.E., Sanchez-Villeda, H., Schroeder, S., McMullen, M.D. 2009. Genetic Diversity and Selection in Maize Genes for Amino Acid Pathways. Maydica. 54:375-386.
Interpretive Summary: As a food and feed crop, maize is deficient in several essential amino acids, including tryptophan, lysine, and methionine. Prior studies demonstrated that several genes involved in the synthesis of amino acids exhibited a decrease in genetic diversity in maize relative to its wild ancestor, teosinte, due to artificial selection during domestication or crop improvement. This reduction in diversity can limit researchers in their ability to alter amino acid content for improved nutritional quality. In this study, we sequenced 16 additional genes involved in amino acid synthesis in a panel of maize inbred lines and teosinte accessions, and conducted several tests of selection. Our study identified five ‘selected’ and 11 unselected clarifying the approaches that may be best exploited by plant breeders and geneticists for improving amino acid content. This research will impact geneticists in their attempts to understand the genetic determinants of amino acid content, and other plant scientists who will try to design more nutritious crop plants through either classical breeding or biotechnology.
Technical Abstract: The objective of crop improvement is to enhance a trait phenotype through breeding and/or biotechnology. Most methods used to determine the genetic basis of agronomic traits rely on genetic variation in order to make marker-phenotype associations. If variation at key loci is reduced, however, due to selection during crop domestication and/or improvement, then analyses may fail to identify these genes as important loci in controlling trait expression. Therefore, it is of practical importance to determine the level of genetic diversity present in crop germplasm for key genes controlling agronomic traits. Results from recent large scale selection screens in maize (Zea mays L.) have revealed that a number of genes involved in amino acid synthesis exhibit signs of selection. In the current study, we asked whether other genes in amino acid pathways were targets of selection, and to what extent has amino acid metabolism in maize experienced artificial selection. We resequenced 16 candidate genes encoding structural enzymes in amino acid metabolism and regulatory proteins implicated in amino acid metabolism in diverse samples of maize inbred lines and teosinte accessions, and conducted multiple tests of selection to identify targets of selection. Here we demonstrate that five of the 16 additional genes involved in amino acid metabolism exhibit some evidence for selection. However, amino acid synthesis pathways as a whole do not show evidence of greatly reduced genetic diversity. Therefore, our results indicate that limited genetic diversity is impacting improvement of the nutritional quality of maize for only a few specific amino acids.