Allele Mining of Exotic Maize Germplasm to Enhance Macular Carotenoids

Abstract

Lutein and zeaxanthin are commonly referred to as the macular carotenoids, as they are localized to ocular tissues and their loss is associated with age-related macular degeneration. Thirty-four high-carotenoid (HiC) lines exhibiting uniquely high concentrations of carotenoids resulted from alíele mining of the Orange Flint race using traditional breeding techniques and visual selection for deep orange endosperm color. Total carotenoid concentrations of the HiC lines ranged from 50 to 101 pg g"^ dry weight (DW) with iutein and zeaxanthin concentrations as high as 66 and 65 pg g'' DW, respectively, levels higher than reported in previous germplasm surveys. The HiC lines fall into three classes based on the accumulation of the major carotenoid: "high-lutein," "high-zeaxanthin," and "balanced." Significant year effects were observed for carotenoid concentrations but not for profiles. During kernel development the pattern of carotenoid accumulation in the HiC lines did not appear to be different than in yellow corn belt dent lines. Collectively, the HiC lines represented only one yi haplotype, 10 unique haplotypes of IcyE, and two unique haplotypes at crtRBL Interestingly, previously identified diagnostic polymorphisms within IcyE did not appear to be useful in distinguishing between high-lutein and high-zeaxanthin HiC lines, and high .i-carotene levels were achieved despite the presence of a suboptimal crtRBi alíele. The HiC lines illustrate the utility of mining allelic variation from exotic sources coupled with the power of simple visual selection and the potential limitations of diagnostic polymorphisms.

Accruing genetic gain in pro-vitamin A enrichment from harnessing diverse maize germplasm

“…Extensive studies were conducted to characterize concentrations of carotenoids in diverse tropical and temperate maize germplasm and found considerable natural genetic variations in accumulation of provitamin A and other carotenoids (Blessin et al 1963;Kurilich and Juvik 1999;Egesel et al 2003;Berardo et al 2004;Islam et al 2004;Chander et al 2008;Vallabhaneni and Wurtzel 2009;Burt et al 2011;Muthusamy et al 2015). To assess the extent of variation in carotenoid composition and content in adapted germplasm available for breeding, we also evaluated 421 tropical-adapted yellow to orange endosperm maize inbred lines in several independent trials (Menkir et al 2008).…”

“…Perhaps the formation of broad-based synthetics from tropicaladapted maize inbred lines displaying different carotenoid composition and content that also contain diverse exotic germplasm in their genome and subjecting them to recurrent selection can be a viable strategy to increase accumulation of favorable alleles of the different genes in the populations. Additional infusion of orange flint germplasm from Argentina and other countries with known potential to contribute high levels of zeaxanthin and lutein (Burt et al 2011) into these broad-based synthetics can further diversity and expand their genetic base and increase the probability of generating lines combining carotenes and xanthophylls to much higher levels. During each selection cycle, visual assessment for desirable kernel properties and agronomic features coupled with screening for favorable allele-specific markers of LcyE, CrtRB1 and other genes (Harjes et al 2008;Yan et al 2010;Wurtzel et al 2012;Owens et al 2014) may allow efficient selection of progenies with combination of alleles of these genes for recombination to further improve the populations.…”

Heterosis for carotenoid concentration and profile in maize hybrids

“…Five yellow dent inbred maize lines (A632, A619, CG33, CG60, and CG102); two white inbred lines (cgx333 and SD80); and 13 high-carotenoid inbred lines (HiC2,HiC3,HiC7,HiC8,HiC9,HiC16,HiC17,HiC21,HiC23,HiC24,HiC25,HiC26,and HiC31) (Burt et al 2011) were used in this study. A632 and CG60 were chosen as they both exhibit carotenoid profiles that are higher in zeaxanthin relative to lutein (Burt et al 2011).…”

“…For instance, the p1 gene, encoding a Myb-like transcription factor, can account for 35%-60% of the total phenotypic variation for maysin concentrations, depending on the particular mapping population (McMullen et al 1998). Work on the carotenoid pathway (Burt et al 2011) showed that effective allele mining from exotic populations using simple visual selection for deep orange endosperm colour could achieve very high carotenoid levels and different carotenoid profiles that could not be adequately explained by the diagnostic polymorphisms suggested by Harjes et al (2008) or Yan et al (2010). This suggests that there is, at least in some populations, potential for drastic improvement of carotenoid content and profile involving loci other than LcyE or CrtRB1.…”

Influence of the moisture at harvest and drying process of the grains on the level of carotenoids in maize (Zea mays)

“…Interest in dietary carotenoids comes from their precursors of vitamin A, antioxidant properties and the association between carotenoid deficiencies and many chronic human diseases (Burt et al, 2011(Burt et al, , 2013. Breeding to increase β-carotene levels in cereal grains, termed provitamin A biofortification, is an economical approach to address dietary vitamin A deficiency in the developing world (Dwens et al, 2014).…”