Washington, D.C.,
March 21, 2010
A team of scientists has discovered rare variations of a maize gene (crtRB1) that can lead to an 18-fold increase in beta-carotene content of maize in an academic research setting. Plant breeders are starting to use these naturally occurring genetic variations to breed maize that can provide more beta-carotene to malnourished people. The body converts beta-carotene into vitamin A.
Millions of people in developing countries are too poor to buy foods rich in beta-carotene, such as fruits and vegetables. This results in vitamin A deficiency, which blinds up to 500,000 children annually. The poor eat cheaper staple foods, such as maize, daily. Increasing the amount of naturally produced beta-carotene in maize can upgrade its status to a ‘superfood’ that provides a valuable nutrient in addition to calories.
Most of the beta-carotene produced in maize is converted into other carotenoids, which make less or no vitamin A. The favorable variations of the crtRB1 gene slow down this conversion process resulting in more beta-carotene, and hence, more vitamin A. The team also identified a molecular marker, essentially a genetic signpost, which makes the most favorable form of the gene easier to find. “We can now, not only search for this form of the gene in maize using cheap molecular markers, but also breed it into any maize variety in the world,” says Dr. Torbert Rocheford, a member of the team. “This could translate into improving the health of children through better nutrition, especially in Africa where maize is a popular staple food.”
“We are on track to release conventionally-bred vitamin A maize in Zambia by 2012—beyond that, this research could accelerate breeding of maize with even more vitamin A,” says Dr. Howarth Bouis, Director of HarvestPlus, which along with USAID and other organizations funded this research. Under the best scenario, the crtRB1 gene variations can increase concentration of beta-carotene from a little above zero, to about 57% of the micronutrient target (15 micrograms/gram beta-carotene) that HarvestPlus has determined would improve poor people’s nutrition and health.
Article Reference:
Rare genetic variation at Zea mays crtRB1 increases β-carotene content in maize grain. Nature Genetics, March 21,2010
Advance Online Publication. DOI:10.1038/ng.551
ABSTRACT:
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. Experimental evidence from association and linkage populations in maize (Zea mays L.) demonstrate that the gene encoding β-carotene hydroxylase 1 (crtRB1) underlies a principal quantitative trait locus associated with β-carotene concentration and conversion in maize kernels. crtRB1 alleles associated with reduced transcript expression correlate with higher β-carotene concentrations. Genetic variation at crtRB1 also affects hydroxylation efficiency among encoded allozymes, as observed by resultant carotenoid profiles in recombinant expression assays. The most favorable crtRB1 alleles, rare in frequency and unique to temperate germplasm, are being introgressed via inexpensive PCR marker-assisted selection into tropical maize germplasm adapted to developing countries, where it is most needed for human health.
Photo: Farmer in Laos shows off his maize
Photo credit: Neil Palmer (CIAT)
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