Molecular breeding for Quality Protein Maize (QPM)

Abstract

Maize endosperm protein is deficient in two essential amino acids, lysine and tryptophan. Several spontaneous and induced mutations that affect amino acid composition in maize have been discovered amongst which the o2 gene (opaque2) has been used in association with endosperm and amino acid modifier genes for developing Quality Protein Maize (QPM), which contains almost double the amount of endosperm lysine and tryptophan as compared to the normal/non-QPM maize. These increases have been shown to have dramatic impacts on human and animal nutrition, growth and performance. A range of hard endosperm QPM germplasm has been developed at the International Maize and Wheat Improvement Center (CIMMYT) mostly through conventional breeding approaches to meet the requirements of various maize growing regions across the world. Microsatellite markers located within the o2 gene provided opportunities for accelerating the pace of QPM conversion programs through marker-assisted selection (MAS). More recently, CIMMYT scientists are striving to develop reliable, easy-to-use markers for endosperm hardness and free amino acid content in the maize endosperm. Recent technological developments including high throughput, single seed-based DNA extraction, coupled with low-cost, high density SNP genotyping strategies, and breeder-ready markers for some key adaptive traits in maize, promise enhanced efficiency and cost effectiveness of MAS in QPM breeding programs. Here, we present a summary of QPM research and breeding with particular emphasis on genetic and molecular basis of o2, epistasis between o2 and other high-lysine mutant genes, and the recent advances in genomics technologies that could potentially enhance the efficiency of molecular breeding for QPM in the near future.