A foundation for provitamin A biofortification of maize: genome-wide association and genomic prediction models of carotenoid levels.
Bottom Line: Significant associations at the genome-wide level were detected within the coding regions of zep1 and lut1, carotenoid biosynthetic genes not previously shown to impact grain carotenoid composition in association studies, as well as within previously associated lcyE and crtRB1 genes.This revealed dxs2 and lut5, genes not previously associated with kernel carotenoids.In genomic prediction models, use of markers that targeted a small set of quantitative trait loci associated with carotenoid levels in prior linkage studies were as effective as genome-wide markers for predicting carotenoid traits.
Affiliation: Department of Agronomy, Purdue University, West Lafayette, Indiana 47907.Show MeSH
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Mentions: Carotenoids are essential to many aspects of animal health, yet animals do not synthesize carotenoids, with the exception of the pea aphid (Moran and Jarvik 2010), and therefore must obtain them from their diet to meet minimal nutritional requirements. The most abundant provitamin A carotenoids in plant-based foods are β-carotene (two retinyl groups), β-cryptoxanthin (one retinyl group), and α-carotene (one retinyl group), but in most plant tissues they are substrates for hydroxylation reactions that produce the dihydroxyxanthophylls lutein and zeaxanthin (Figure 1)—the most prevalent carotenoids in vegetative and seed tissues (Howitt and Pogson 2006; Cazzonelli and Pogson 2010). The carotenoid biosynthetic pathway is conserved in plants and has been best characterized in the model dicot Arabidopsis thaliana (Dellapenna and Pogson 2006; Kim et al. 2009; Cuttriss et al. 2011) in which the molecular basis of these hydroxylation steps is well understood. The committed step of the carotenoid pathway is formation of phytoene from geranylgeranyl diphosphate (GGPP) by phytoene synthase (PSY) (Figure 1). A subsequent key branch point occurs at the level of lycopene cyclization. Lycopene β-cyclase activity at both ends of the molecule produces β-carotene, while addition of one β-ring and one ε-ring by lycopene ε-cyclase produces α-carotene. Hydroxylation of one β-carotene ring produces β-cryptoxanthin followed by hydroxylation of the other β-ring to produce zeaxanthin. Similarly, hydroxylation of the β-ring of α-carotene produces zeinoxanthin, and subsequent hydroxylation of the ε-ring yields lutein.
Affiliation: Department of Agronomy, Purdue University, West Lafayette, Indiana 47907.