Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2009
Publication Date: 4/12/2010
Citation: Gutierrez-Rojas, A., Betran, J., Scott, M.P., Atta, H., Menz, M. 2010. Quantitative Trait Loci for Endosperm Modification and Amino Acid Contents in Quality Protein Maize. Crop Science. 50:870-879.
Interpretive Summary: In order to improve the nutritional value of corn grain, plant breeders use the opaque2 mutation. This mutation increases the levels of the essential amino acids lysine and tryptophan in the grain. This mutation also introduces problems such as reduced yield and seed quality. These problems are typically overcome by breeding, and agronomically adapted maize carrying the opaque2 mutation is called quality protein maize. Breeding to ameliorate the shortcomings of opaque2 is a time-consuming and expensive process. We identified genetic loci controlling the grain phenotypes of interest to Quality Protein Maize (QPM) breeders. This information provides a better understanding of the genetic control of these traits and provides breeders with molecular markers for the traits that will facilitate selection of superior genotypes. Ultimately, this will reduce the cost and accelerate the rate of gain in QPM breeding programs, making nutritionally superior more widely available and providing health benefits to people who depend on maize in their diets.
Technical Abstract: The deficient protein quality of corn grain can be improved by replacing the normal Opaque2 (O2) alleles with non-functional mutant alleles o2. Unfortunately, o2 alleles are associated with a very soft endosperm texture, poor yield and susceptibility to diseases and insects. Plant breeders have been able to restore a desirable ratio of hard to soft endosperm in o2 germplasm. These modified genotypes are known as Quality Protein Maize (QPM). Neither the mechanism nor the genetic components controlling endosperm modification in QPM lines are well understood. Using a population of recombinant inbred lines (RILs), derived from a cross between an o2 line and a QPM line and a novel evaluation method for endosperm modification, quantitative trait loci (QTL) were mapped for traits related to the modification of endosperm texture and the content of the essential amino acids lysine, tryptophan and methionine. For endosperm texture traits, QTL clusters were detected on chromosomes 3, 5, 6 and 8, together accounting for 62-68% of the observed variation. For traits related to amino acid contents, QTL clusters were located on chromosomes 7 and 8 that explained up to 39% of the observed variation. The elucidation of the genetic mechanisms of the modification of o2 endosperm and essential amino acid contents will provide valuable information and important tools to plant breeders as well as plant scientists interested in improving the quality of cereal grain.