Location: Plant, Soil and Nutrition ResearchTitle: Genome-wide association study and pathway level analysis of tocochromanol levels in maize grain Author
|Buckler, Edward - Ed|
Submitted to: Genes, Genomes, Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2013
Publication Date: 6/3/2013
Citation: Lipka, A.E., Gore, M., Magallanes-Lundback, M., Mesberg, A., Lin, H., Tiede, T., Chen, C., Buell, R.C., Buckler IV, E.S., Rocheford, T., Dellapenna, D. 2013. Genome-wide association study and pathway level analysis of tocochromanol levels in maize grain. Genes, Genomes, Genetics. DOI: 10.1534/g3.113.006148. Interpretive Summary: Tocopherols and tocotrienols, collectively called tocochromanols, are a group of compounds found in maize that exhibit vitamin E and antioxidant activity. Given that individual tocochromanol compound levels vary substantially in the maize kernel, identification of genes associated with these compounds could result in maize with higher nutritional levels. To this end, we conducted a genetic analysis of tocochromanol compound levels in a collection of maize samples representing a significant portion of the genetic diversity present in public maize breeding programs. In addition to providing further insight into a major gene responsible for increasing vitamin E activity, we also identified novel associations between three genes and tocochromanol activity. Selection on these four genes could make it possible to simultaneously boost tocopherol and tocotrienol levels in maize kernels, resulting in larger quantities of vitamin E and antioxidants available for human consumption.
Technical Abstract: Tocopherols and tocotrienols, collectively known as tocochromanols, are the major lipid-soluble antioxidants in maize (Zea mays L.) grain. Given that individual tocochromanols differ in their degree of vitamin E activity, variation for tocochromanol composition and content in grain from among diverse maize inbred lines has important nutritional and health implications for enhancing the vitamin E and antioxidant contents of maize-derived foods through plant breeding. Toward this end, we conducted a genome-wide association study of six tocochromanol compounds and fourteen of their sums, ratios, and proportions with a 281 maize inbred association panel that was genotyped for 591,822 SNP markers. In addition to providing further insight into the association between ZmVTE4 (y-tocopherol methyltransferase) haplotypes and a-tocopherol content, we also detected a novel association between ZmVTE1 (tocopherol cyclase) and tocotrienol composition. In a pathway level analysis, we assessed the genetic contribution of 60 a priori candidate genes encoding the core tocochromanol pathway (VTE genes) and reactions for pathways supplying the isoprenoid tail and aromatic head group of tocochromanols. This analysis identified two additional genes, ZmHGGT1 (homogentisate geranylgeranyltransferase) and one prephenate dehydratase parolog (of four in the genome) that also modestly contribute to tocotrienol variation in the panel. Collectively, our results provide the most favorable ZmVTE4 haplotype and suggest three new gene targets for increasing vitamin E and antioxidant levels through marker-assisted selection.