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Researchers at Duke University Medical Center have traced the biochemical
pathway by which plants build a compound that compromises the quality of
corn and soybeans as an animal feed. Their studies indicate that it is
feasible to engineer such plants to significantly improve their quality as
animal feeds -- a potentially important boon to the hog and poultry
industries, said the researchers, August 2005.

The researchers, led by Howard Hughes Medical Institute investigator John
York, published their findings the week of August 15 in the online Early
Edition of the Proceedings of the National Academy of Sciences. Lead author
on the paper was Jill Stevenson-Paulik in the York laboratory. Their
research was supported by the National Institutes of Health.

In their studies, the researchers sought to understand the biochemical
pathway that leads to the synthesis in plants of the chemical called
phytate. In the plant, this molecule is a regulator of signaling in the
cell; and in seeds, it acts as a phosphate storage molecule.

Phytate also acts as an "antinutrient" for animals, mainly pigs and
chickens, that consume such grains, said Stevenson-Paulik. "Phytate is a
very abundant compound in plant seeds that compromises the nutrition in the
animals that consume it as their main food source. It binds such minerals as
calcium and iron very well, and since it is not digested, animals that
consume grains with phytate will lose these minerals as the phytate passes
through their gut."

What's more, said the researchers, such excreted phytate contributes to
environmental phosphorus pollution, because it washes into surface waters
causing the abnormal growth of aquatic plant life called eutrophication.

According to Stevenson-Paulik, creating low-phytate strains of feed grains
was hindered by the lack of knowledge about the later biochemical pathways
by which phytate is synthesized in plants.

In their studies, Stevenson-Paulik, York and their colleagues drew on their
previous studies in yeast that enabled them to understand the biochemical
pathways for producing phytate. Using those insights, they searched for
counterpart genes in the mustard plant Arabidopsis -- a widely used model
plant in genetic studies.

Their analysis revealed that the genes for two particular enzymatic
regulatory switches, called kinases, were central to the final steps of
phytate synthesis. What's more, they found that genetic mutations that
knocked out both these switches -- called AtlPK1 and AtlPK2_ -- nearly
eliminated phytate production in the resulting Arabidopsis seeds.

Said York, "Perhaps one of the most important aspects of Jill's work is the
finding that it wasn't just knocking out the last step in phytate synthesis
that was important. Knocking out the last two steps really reduced seed
phytate. And what was very unexpected and quite significant is that just
knocking out one gene resulted in a buildup of toxic precursor compounds in
the seeds." Also, found the researchers, the phytate-eliminating mutations
did not compromise seed yield, and also increased the phosphate levels in
the seeds.

"The amount of free phosphate in the double mutant is dramatically increased
over what is found in nature," said Stevenson-Paulik. "And that has a great
benefit in terms of nutrition, because it provides more available
phosphorous for the animals that would eat grains with such properties."

According to York, a patent on the low-phytate strains has been applied for,
and discussions have been initiated with feed companies about production of
such grains. "The next step is to move this process into a commercial
environment so that companies can begin producing low-phytate strains in
their crop line," he said.

Besides York and Stevenson-Paulik, other co-authors of the paper were Robert
Bastidas, Shean-Tai Chiou, all in the Duke Department of Pharmacology and
Cancer Biology, and Roy Frye of the Pittsburgh VA Medical Center.

[www.eurekalert.org]

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