Ithaca, New York
January 17, 2008
 Up
to 250 million children, many in the sub-Saharan Africa region,
are at risk each year for health disorders -- including 40
million who develop a sight-threatening eye disease -- all
because they do not get enough vitamin A in their diet.
A new discovery, spearheaded by
Cornell University and
University of Illinois plant geneticists and published in
the Jan. 18 issue of the journal
Science, could change all
that. Using genetic and statistical tools, researchers have
identified a set of genetic variants in maize that accounts for
levels of vitamin A precursors among varieties.
The research could lead to at least tripling the provitamin A
levels [the precursor to vitamin A] in Africa's maize, said
senior author Edward Buckler (photo), a
U.S. Department of
Agriculture-Agricultural Research Station research
geneticist in Cornell's Institute for Genomic Diversity and
Cornell adjunct associate professor of plant breeding and
genetics.
"By identifying these genetic variants, breeders can make
varieties with higher provitamin A rapidly and inexpensively,"
said Buckler.
"This research will now go into the major effort to help create
maize varieties in sub-Saharan Africa for subsistence farmers."
These improved crops, he noted, will not be genetically
engineered but use the natural variation that is found in maize
varieties, unlike rice, which has no genetic variation for
provitamin A and so scientists use transgenes, or genetic
engineering, to boost its provitamin A content.
Maize is the dominant subsistence crop in sub-Saharan Africa and
Latin America, where 17 percent to 30 percent of children under
age 5 are vitamin A deficient, said Buckler.
"Since maize is consumed for all three meals a day in much of
Africa, maize is a good target for biofortification," he added.
Buckler is credited with improving association mapping, one of
the methods used for this research, that is being used to
understand the genetic basis of such complex traits as vitamin A
content, drought tolerance, nitrogen use, carbon metabolism,
diseases, and crop and milk yields.
The research was supported by the
National Science Foundation,
the U.S. Department of Agriculture and the Harvest Plus program.
RELATED RELEASE from the
University of Illinois
Team finds an
economical way to boost the vitamin A content of maize
A team of plant geneticists and
crop scientists has pioneered an economical approach to the
selective breeding of maize that can boost levels of provitamin
A, the precursors that are converted to vitamin A upon
consumption. This innovation could help to enhance the
nutritional status of millions of people in the developing
world.
The new method is described this week in the journal Science.
The team includes scientists from Cornell University, the
University of Illinois, Boyce Thompson Institute, DuPont Crop
Genetics Research, the University of North Carolina, the City
University of New York, the International Maize and Wheat
Improvement Center and the U.S. Department of Agriculture.
The innovation involves a new approach for selecting the parent
stock for breeding maize, and significantly reduces the
ambiguity and expense of finding varieties that yield the
highest provitamin A content available. As part of this
investigation, the researchers have identified a naturally
mutated enzyme that enhances the provitamin A content of maize.
Vitamin A deficiency is a leading cause of eye disease and other
health disorders in the developing world. Some 40 million
children are afflicted with eye disease, and another 250 million
suffer with health problems resulting from a lack of dietary
vitamin A.
“Maize is the dominant subsistence crop in much of Sub-Saharan
Africa and the Americas,” the researchers write, “where between
17 and 30 percent of children under the age of 5 are vitamin A
deficient.”
Maize also is one of the most genetically diverse food crops on
the planet, said Torbert Rocheford, a professor of nutritional
sciences at Illinois and a corresponding author on the paper.
This diversity is tantalizing to those hoping to make use of
desirable traits, but it also provides a formidable challenge in
trying to understand the genetic basis of those attributes.
One hurdle to increasing the provitamin A content of maize has
been the expense of screening the parent stock and progeny of
breeding experiments, Rocheford said.
A common technique, called high performance liquid
chromatography (HPLC), can assess the provitamin A content of
individual plant lines. But screening a single sample costs $50
to $75, he said.
“That’s really expensive, especially since plant breeders like
to screen hundreds or more plants per cycle, twice a year,” he
said. “The cost was just prohibitive.”
The new approach uses much more affordable methods and gives a
more detailed picture of the genetic endowment of individual
lines. One technique the researchers employed, called
quantitative trait loci (QTL) mapping, allowed them to identify
regions of the maize chromosomes that influence production of
the precursors of vitamin A. They also used association mapping,
which involves studying variation in selected genes and tracking
inheritance patterns to see which form of a gene coincides with
the highest provitamin A content. Polymerase chain reaction
(PCR) allowed them to amplify and sequence the different
versions (alleles) of the genes of interest, to find the alleles
that boosted levels of vitamin A precursors in the plant.
This approach led to an important discovery. The team found a
mutant form of an enzyme vital to the cascade of chemical
reactions that produce the precursors of vitamin A in the plant.
This mutant is transcribed in lower quantities than the normal
allele and steers the biochemistry toward producing higher
levels of vitamin A precursors.
The study analyzed 300 genetic lines selected to represent the
global diversity of maize, and identified some varieties that
came close to the target amount of 15 micrograms of
beta-carotene (a form of provitamin A) per gram. Current maize
varieties consumed in Africa can have provitamin A content as
low as 0.1 micrograms per gram.
The researchers can now inexpensively screen different maize
varieties for this allele and breed those that contain it to
boost the nutritional quality of the maize, said Rocheford, who
also is affiliated with the Institute for Genomic Biology.
Other news
from
the University of Illinois
RELATED RELEASE from the
U.S. National Science Foundation
Feeding the world: new method for
producing high-vitamin corn could improve nutrition in
developing countries
Scientists have developed a potentially powerful new tool in the
fight against deficiencies in dietary vitamin A, which cause eye
diseases, including blindness, in 40 million children annually,
and increased health risks for about 250 million people, mostly
in developing countries.
This tool consists of "a new method of analyzing the genetic
makeup of corn that will enable developing countries to identify
and increase cultivation of corn that has naturally high levels
of vitamin A precursors," says Ed Buckler, a co-leader of the
research team from the U.S. Department of Agriculture,
Agricultural Research Service and Cornell University
Corn is an essential part of the diets of hundreds of millions
of people around the world, many of whom live in developing
countries. Regular consumption by adults and children of
adequate quantities of corn high in vitamin A precursors, which
are converted in the human body into vitamin A, would reduce
their chances of developing vitamin A deficiencies and
associated health problems.
This new method of increasing cultivation of high-vitamin corn
is designed to tap the natural genetic diversity of corn. It was
developed by a team led by Buckler and Torbert Rocheford of the
University of Illinois, and was partially funded by The National
Science Foundation (NSF). It will be described in the January
18, 2007 edition of Science.
"In a field of thousands of ears of corn, each ear has a
slightly different genetic makeup and resulting differences in
physical characteristics, including levels of vitamin A
precursors -- just like every person in a crowd has a slightly
different genetic makeup and associated physiological
differences," explains James Collins, assistant director for the
Biological Sciences Directorate at NSF. But only a very small
percentage of corn crops are genetically programmed to have
naturally high levels of vitamin A precursors, and these
high-vitamin ears cannot be identified merely by visual
inspection. "Therefore, identifying crops that have high levels
of vitamin A precursors has traditionally been like finding a
needle in a haystack."
But the team led by Buckler and Rocheford has significantly
simplified the task of sifting through that proverbial haystack.
They did so by identifying genetic markers in corn that are
associated with high levels of vitamin A precursors. These
markers can be used by "scientists working in very basic labs in
developing countries to quickly screen for local corn strains
that are high in vitamin A precursors," says Buckler. Then,
these high-vitamin strains may be bred, cultivated and consumed
by local people.
Corn is the dominant subsistence crop in sub-Saharan Africa and
Latin America, where 17 to 30 percent of children under age five
are vitamin A deficient, says Buckler. Because corn is consumed
for all three meals a day in much of Africa, it is a good target
for vitamin biofortification, he added.
Buckler says that his team's method for analyzing the genetic
makeup of corn is "much simpler and faster and up to 1,000-fold
cheaper" than running the types of chemical tests that were
previously available for identifying corn high in vitamin A
precursors. He expects it to significantly accelerate the
vitamin biofortification of corn crops.
The Buckler and Rocheford team is currently working with various
international organizations, such as CIMMYT (the International
Maize and Wheat Improvement Center) and the International
Institute for Tropical Agriculture, to help train plant breeders
in developing countries to use their techniques.
Buckler says that this new method of increasing cultivation of
high-vitamin corn was made possible by recent breakthroughs in
statistical analyses and the advent of rapid DNA sequencers --
instruments that are used to automate genetic profiling of
crops. The researchers expect this new method to have broad
applications beyond corn improvement.
Other news
from the U.S. National
Science Foundation |
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