GAINESVILLE---Tiny algae -- which form green scum on ponds -- are thesource of a unique gene that can be transferred to crop plants, boostingyields by as much as 30 percent, according to University of Floridaresearchers.
"It's another big step forward in the green revolution for more efficientand abundant agricultural production to feed a hungry world," said RobertSchmidt, plant molecular biologist with the UF's Institute of Food andAgricultural Sciences, who isolated the gene from a common pond alga.
He said the gene allows the alga to use nitrogen nutrients far moreefficiently than regular crop plants.
"When pure cultures of this organism were grown in a nutrient mediumcontaining nitrate as their sole source of nitrogen, they would grow at acertain rate. When the nitrate was replaced with ammonium, its growth rateincreased 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 nothave. The GDH enzyme -- short for ammonium-inducible glutamate dehydrogenase-- increases the efficiency by which ammonium is incorporated into proteinsand other components for more rapid cell growth.
"We soon realized this might be a good trait to be placed into crop plantsand began the process of isolating, cloning and sequencing the gene from thealga," Schmidt said.
After more than 10 years of research, a patent is expected to be issued thisSpring for use of the GDH gene in genetically modified crop plants producedin collaboration with Monsanto Co. in St. Louis. Schmidt and Monsantoscientist Philip Miller, who studied under Schmidt and received his UFdoctoral degree in microbiology and cell science in 1994, inserted the algalgene into wheat plants to see how this crop plant would perform.
In preliminary trials, genetically modified wheat plants with the new traitwere more robust, grew larger and produced significantly more grain thanconventional wheat plants on the same amount of nitrogen fertilizer. One ofSchmidt's alga genes is already patented by UF, and a patent is pending onanother.
Schmidt said an additional benefit to growers is that it may be possible tocut nitrogen fertilizer levels for these genetically modified plants byabout one-third and still obtain the same grain yields. This, he added,would be especially valuable in developing countries where nitrogenfertilizer is a costly nutrient and a major constraint to higher cropyields. The thriftier plants also would reduce leaching of nutrients intowaterways and groundwater. "This discovery could have a positive impact on the economy of worldagriculture, particularly if the productivity of other crop plants can beincreased by inserting this GDH gene," Schmidt said. "Moreover, this greenalga may serve as a source of other novel genes that can be used in plantbiotechnology, giving crops more desirable traits to increase or maintainproductivity over a wide range of nutritional and environmental conditions." Schmidt and other UF researchers are already studying how this algal geneand others might improve crop plants' ability to tolerate drought, heat andsalinity.
He said crop plants absorb nitrate from the soil and then reduce it in twosteps to form ammonium, which then is incorporated into carbon compounds toform amino acids. Protein and other plant constituents are built from theseamino acids, but these reduction and incorporation steps are very energycostly to the plant. That's why genetic engineers are trying to improve theefficiency of one or more of these steps.
"When we began studying tiny [algae] commonly found on the surface ofpond water, many people in the scientific community thought we were barkingup the wrong tree, but we knew that micro algae must grow very rapidly tocompete with bacteria living in the pond," Schmidt said. "To compete, the alga must perform very efficiently, and we thought thisability could be transferred to higher plants to make them more efficient,too."
Other researchers in Schmidt's laboratory who made significant contributionsto the biotech project include Waltraud Dunn, biological scientist, and MarkCock, postdoctoral research associate. Schmidt credited Cock for most ofthe initial work on GDH gene isolation and characterization.
Materials provided by University Of Florida, Institute Of Food And Agricultural Sciences. Note: Content may be edited for style and length.
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