ENHANCING CORN WITH RESISTANCE TO AFLATOXIN CONTAMINATION AND INSECT DAMAGE
Location: Corn Host Plant Resistance Research
Title: Genetic Association Mapping Identifies Single Nucleotide Polymorphisms in Genes that Affect Abscisic Acid Levels in Maize Floral Tissues During Drought
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 2010
Publication Date: November 17, 2010
Citation: Setter, T.L., Yan, J., Warburton, M.L., Ribaut, J., Xu, Y., Sawkins, M., Buckler, E.S., Zhang, Z., Gore, M.A. 2010. Genetic association mapping identifies single nucleotide polymorphisms in genes that affect abscisic acid levels in maize floral tissues during drought. Journal of Experimental Botany. 62:701-716. doi:10.1093/jxb/erq308.
Interpretive Summary: Maize is a major staple for billions of people worldwide, but is sensitive to the unpredictable weather patterns caused by climate change. Drought tolerance is now needed even in crop plants that have traditionally been grown in areas of the world with higher rainfall, because in any given year, sufficient rainfall is not guaranteed. Drought tolerance is a highly complex trait, and is the result of interactions between many genes and metabolic pathways in a plant. Two major metabolites influencing drought tolerance in maize are sugars (glucose and sucrose) and abscisic acid (ABA). Genes in the pathways for the production and subsequent breakdown of these and related compounds in maize were tested to see if they were associated with drought tolerance via gene sequencing, genotyping, and association analysis. Differences in the genes carried by more drought tolerant maize plants were found. These differences can now be used to breed more drought tolerant maize for the world.
In maize, development of the female inflorescence and its floral parts is vulnerable to water stress at flowering, which causes loss of kernel set and productivity. While changes in the levels of sugars and abscisic acid (ABA) are thought to play a role in this stress response, the mechanistic basis and genes involved are not known. A candidate gene approach was used with association mapping to identify loci involved in accumulation of carbohydrates and ABA metabolites during stress. A panel of single nucleotide polymorphisms (SNPs) in genes from these metabolic pathways, and in genes for reproductive development and general drought tolerance was used to genotype 350 tropical and subtropical maize inbred lines. The same lines were phenotyped under well watered or drought conditions; drought was imposed during flowering, and pre-pollination ears, silks and leaves were analyzed for sugars (glucose, sucrose), starch, and ABA metabolites (ABA, ABA-glucose ester, phaseic acid) and the compatible osmolyte proline. Data were corrected for population stratification and kinship, and analyzed for trait-SNP association with a mixed model. ABA and sugar levels in silks and ears were negatively correlated with growth of silks and ears. Association mapping identified a SNP in the maize homolog of the Arabidopsis MADS-box gene, PISTILLATA, which was significantly associated with phaseic acid in ears of well-watered plants, and a SNP in pyruvate dehydrogenase kinase, a key regulator of carbon flux into respiration, that associated with silk sugar concentration. SNPs in two aldehyde oxidase genes on chromosome 1 were significantly associated with ABA levels in silks of water stressed plants. Given the short range over which decay of linkage disequilibrium (LD) occurs in maize, we suggest that allelic variation in these genes affects ABA and carbohydrate relationships in floral tissues during drought, and provides targets for selection of more favorable alleles at these loci to improve drought tolerance.