Validation of the effects of molecular marker polymorphisms in LcyE and CrtRB1 on provitamin A concentrations for 26 tropical maize populations

Abstract

Vitamin A deficiency (VAD) compromises immune function and is the leading cause of preventable blindness in children in many developing countries. Biofortification, or breeding staple food crops that are rich in micronutrients, provides a sustainable way to fight VAD and other micronutrient malnutrition problems. Polymorphisms, with associated molecular markers, have recently been identified for two loci, LcyE (lycopene epsilon cyclase) and CrtRB1 (β-carotene hydroxylase 1) that govern critical steps in the carotenoid biosynthetic pathway in maize endosperm, thereby enabling the opportunity to integrate marker-assisted selection (MAS) into carotenoid breeding programs. We validated the effects of 3 polymorphisms (LcyE5′TE, LcyE3′Indel and CrtRB1-3′TE) in 26 diverse tropical genetic backgrounds. CrtRB1-3′TE had a two-ten fold effect on enhancing beta-carotene (BC) and total provitamin A (proA) content. Reduced-function, favorable polymorphisms within LcyE resulted in 0–30 % reduction in the ratio of alpha- to beta-branch carotenoids, and increase in proA content (sometimes statistically significant). CrtRB1-3′TE had large, significant effect on enhancing BC and total ProA content, irrespective of genetic constitution for LcyE5′TE. Genotypes with homozygous favorable CrtRB1-3′TE alleles had much less zeaxanthin and an average of 25 % less total carotenoid than other genotypes, suggesting that feedback inhibition may be reducing the total flux into the carotenoid pathway. Because this feedback inhibition was most pronounced in the homozygous favorable LcyE (reduced-function) genotypes, and because maximum total proA concentrations were achieved in genotypes with homozygous unfavorable or heterozygous LcyE, we recommend not selecting for both reduced-function genes in breeding programs. LcyE exhibited significant segregation distortion (SD) in all the eight, while CrtRB1 in five of eight digenic populations studied, with favorable alleles of both the genes frequently under-represented. MAS using markers reported herein can efficiently increase proA carotenoid concentration in maize.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-012-1987-3) contains supplementary material, which is available to authorized users.

Genetic variability and inter-relationship of kernel carotenoids among indigenous and exotic maize (Zea maysL.) inbreds

“…It also causes low resistance to infectious diseases and accounts for about 70% of childhood deaths across the world (Black et al 2008). Inbreds thus identified with high β-carotene (~15 µg/g) would be useful in developing provitamin A enriched hybrids to alleviate vitamin A deficiency (VAD) worldwide (Zhang et al 2012;Babu et al 2013).…”

“…Carotenoid profiling using HPLC to assess the concentration of β-carotene is expensive and time consuming. Thus selection based on the markers for favourable alleles of genes causing β-carotene enhancement in the pathway will be an effective approach for developing provitamin Arich maize genotypes (Yan et al 2010;Babu et al 2013) to alleviate VAD worldwide.…”

Progress update: Crop development of biofortified staple food crops under HarvestPlus

“…The most important provitamin A enhancing alleles identified to date are lycopene epsilon cyclase (lcyE) and beta-carotene hydroxylase 1 (crtRB1) [51,52]. Validation experiments showed that the latter alone often doubles, and sometimes triples, the total concentration of provitamin A carotenoid content in maize grain, mainly by increasing the content of beta-carotene [53]. To date, in Africa, more than 40 provitamin A maize synthetics, single-cross hybrids, and three-way hybrids have been released in the DRC, Ghana, Malawi, Mali, Nigeria, Rwanda, Tanzania, Zambia, and Zimbabwe.…”

Orange maize in Zambia: Crop development and delivery experience

“…Subsequently, genetic association mapping studies using three diverse maize germplasm panels, selected to encompass a wide range of carotenoid contents and ratios, were used to identify favorable alleles of genes encoding two key enzymes in the carotenoid biosynthetic pathway, lycopene epsilon cyclase (lycE) and beta-carotene hydroxylase 1 (crtRB1), which substantially affect the accumulation of beta-carotene in grain [27,28,29,30]. By using DNA markers identified for these two enzymes, the screening of germplasm has become faster and cheaper than selection based on HPLC methodology.…”