Jan. 28, 1999 GAINESVILLE---Tiny algae -- which form green scum on ponds -- are the source of a unique gene that can be transferred to crop plants, boosting yields by as much as 30 percent, according to University of Florida researchers.
"It's another big step forward in the green revolution for more efficient and abundant agricultural production to feed a hungry world," said Robert Schmidt, plant molecular biologist with the UF's Institute of Food and Agricultural Sciences, who isolated the gene from a common pond alga.
He said the gene allows the alga to use nitrogen nutrients far more efficiently than regular crop plants.
"When pure cultures of this organism were grown in a nutrient medium containing nitrate as their sole source of nitrogen, they would grow at a certain rate. When the nitrate was replaced with ammonium, its growth rate increased by 40 percent," he said.
To find out why they grow faster, Schmidt discovered this particular alga, Chlorella sorokiniana, has a unique enzyme that regular crop plants do not have. The GDH enzyme -- short for ammonium-inducible glutamate dehydrogenase -- increases the efficiency by which ammonium is incorporated into proteins and other components for more rapid cell growth.
"We soon realized this might be a good trait to be placed into crop plants and began the process of isolating, cloning and sequencing the gene from the alga," Schmidt said.
After more than 10 years of research, a patent is expected to be issued this Spring for use of the GDH gene in genetically modified crop plants produced in collaboration with Monsanto Co. in St. Louis. Schmidt and Monsanto scientist Philip Miller, who studied under Schmidt and received his UF doctoral degree in microbiology and cell science in 1994, inserted the algal gene into wheat plants to see how this crop plant would perform.
In preliminary trials, genetically modified wheat plants with the new trait were more robust, grew larger and produced significantly more grain than conventional wheat plants on the same amount of nitrogen fertilizer. One of Schmidt's alga genes is already patented by UF, and a patent is pending on another.
Schmidt said an additional benefit to growers is that it may be possible to cut nitrogen fertilizer levels for these genetically modified plants by about one-third and still obtain the same grain yields. This, he added, would be especially valuable in developing countries where nitrogen fertilizer is a costly nutrient and a major constraint to higher crop yields. The thriftier plants also would reduce leaching of nutrients into waterways and groundwater. "This discovery could have a positive impact on the economy of world agriculture, particularly if the productivity of other crop plants can be increased by inserting this GDH gene," Schmidt said. "Moreover, this green alga may serve as a source of other novel genes that can be used in plant biotechnology, giving crops more desirable traits to increase or maintain productivity over a wide range of nutritional and environmental conditions." Schmidt and other UF researchers are already studying how this algal gene and others might improve crop plants' ability to tolerate drought, heat and salinity.
He said crop plants absorb nitrate from the soil and then reduce it in two steps to form ammonium, which then is incorporated into carbon compounds to form amino acids. Protein and other plant constituents are built from these amino acids, but these reduction and incorporation steps are very energy costly to the plant. That's why genetic engineers are trying to improve the efficiency of one or more of these steps.
"When we began studying tiny [algae] commonly found on the surface of pond water, many people in the scientific community thought we were barking up the wrong tree, but we knew that micro algae must grow very rapidly to compete with bacteria living in the pond," Schmidt said. "To compete, the alga must perform very efficiently, and we thought this ability could be transferred to higher plants to make them more efficient, too."
Other researchers in Schmidt's laboratory who made significant contributions to the biotech project include Waltraud Dunn, biological scientist, and Mark Cock, postdoctoral research associate. Schmidt credited Cock for most of the initial work on GDH gene isolation and characterization.
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