Biology Reference
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of iron in maize grains, Drakakaki and colleagues
(2005) co-expressed a fungal phytase gene and
a ferritin gene (for enhanced iron storage) in the
maize endosperm so as to enhance the total pool
of iron as well as bioavailability. However, it
should be emphasized that the phytase has to be
heat-resistant so as to remain active when maize
flour is subjected to cooking processes. A suc-
cessful example of thermostable phytase engi-
neering was reported for endosperm-targeted
expression in wheat (Brinch-Pederson et al.
2006). The advantage of such an approach is
that mature seed chemistry is largely unaltered,
thereby reducing significantly the risk for unan-
ticipated negative impacts on plant or seed func-
tion, chemistry, or quality.
Very impressive progress has been made with
respect to genetics and pathway characteriza-
tion of low phytate mutations and encouraging
leads have been obtained in successful engineer-
ing of the “high-phytase” trait in maize seeds.
However, an important fact to remember is that
phytic acid and its anabolic pathways are central
to a number of metabolic, developmental, and
signaling pathways vital to plant function and
productivity, and low phytate may often inadver-
tently lead to low yield or stress susceptibility
(Raboy 2009). Looking to the future, efforts to
develop low-phytate maize cultivars will have to
ensure high yield as well tolerance to abiotic and
biotic stresses, unaccompanied by undesirable
agronomic characteristics. Thermostable “high-
phytase” engineering strategies promise to over-
come a number of undesirable whole plant con-
sequences that are often encountered with “low
phytate”-based approaches.
their breeding programs, while nutritionists and
health professionals accommodate agriculture-
based approaches in their toolbox along with
clinical interventions. The current collaborative
biofortification efforts on maize in CIMMYT,
funded substantially by HarvestPlus, target the
following on a continuing and routine basis:
select and breed nutritionally improved maize
varieties with superior agronomic properties;
carefully test promising varieties under devel-
opment to ensure that the nutrients are suffi-
ciently retained and bioavailable as consumed;
develop efficient and accelerated mechanisms for
testing promising materials with farmers, con-
sumers, and other end users; and measure the
nutritional impacts of these improved varieties in
community-based studies where these varieties
have been adopted.
Looking ahead, a number of new poten-
tial biofortification targets may be discovered
in maize. These include increased concentra-
tion of prebiotics such as inulin, rafinose, and
stachyose, for improved absorption and utiliza-
tion of nutrients; elevated levels of ascorbic
acid in maize endosperm that may result in
enhanced bioavailaibility of micronutrients; and
higher concentrations of tocopherols/VitaminE,
which has number of beneficial antioxidant prop-
erties. The decision as to whether a breeding
program is to be built on these new novel traits
will depend on the nutritional value to disad-
vantaged and marginal communities, the ease
of screening, the extent of germplasm variabil-
ity, the heritability of the trait, and the trait's
correlation with grain yield and other agro-
nomic characteristics. Many important lessons
could be learned from the extensive experience
of institutions such as CIMMYT in developing
and disseminating nutritionally enriched maize
germplasm, especially QPM. These include the
need for: (1) assurance of competitive agro-
nomic performance of the nutritionally enhanced
germplasm (vis-a-vis normal maize); (2) high
throughput, low-cost and easily accessible phe-
notyping/screening tools; (3) generating aware-
ness and capacity building of national partners
on the strengths and constraints (if any) of
Conclusions
Biofortification is an interdisciplinary science
that requires coordinated efforts from breeders,
geneticists, nutritionists, economists, seed sys-
tem specialists, and agricultural extension spe-
cialists. As emphasized by Bouis and Welch
(2010), agricultural science and nutrition have
to be integrated in such a way that plant breeders
incorporate nutrition as a routine target trait in
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