News Release 96-028
Scientists Discover New Class of Genes
May 28, 1996
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Researchers have identified a gene in a common weed that allows the plant to get iron from soil whenever it is starved for the essential nutrient. The National Science Foundation (NSF) funded discovery has important implications for both crop yields and human nutrition.
The researchers, from the University of Minnesota and Dartmouth College, also report that the gene, bears a striking similarity to genes of unknown function in rice, yeast, worms and humans. This suggests that the gene, which was cloned from a small plant related to the mustard family, may be part of a new class of genes involved in controlling the uptake of metals by cells.
When the researchers compared the gene's code to those stored in a data bank containing sequences from hundreds of other organisms, they discovered several closely related sequences, suggesting that they may have discovered a new family of metal transport genes.
David Eide, a microbiologist at the University of Minnesota School of Medicine, and Mary Lou Guerinot, a biologist at Dartmouth College, reported the discovery in the current issue of Proceedings of the National Academy of Sciences.
More than a third of the world's soils are iron- deficient, compromising soil fertility. Iron deficiency is also the leading nutritional disorder in people worldwide. Most of the world's humans get their daily iron supply in the form of plant foods. "Understanding how plants take up this important nutrient could lead to the creation of plants that are more efficient users of iron in soil and richer sources of iron in foods," says Machi Dilworth, director of NSF's integrative plant biology program.
Though iron deficiency is a global nutrition problem, iron overload is lethal to people with an inherited disorder called hemochromatosis, which causes their bodies to store excess iron. Iron has also been implicated as a risk factor in heart disease. "Living things need iron as a nutrient but because it can also be toxic, cells regulate its uptake," explains Guerinot.
Adds Dilworth, "For years, researchers have known that plants that survive iron-poor conditions are able to react to iron deprivation by producing a protein in their roots. This protein converts an unusable form of iron in soil into a form that can be taken up by cells." Yeast use a similar mechanism to obtain iron. Both mechanisms are known to have a genetic basis.
To find the new gene, the researchers inserted pieces of DNA from the weed, which has the Latin name Arabidopsis, into mutant yeast cells known to lack the ability to survive in low-iron conditions. The transformed yeast cells were then grown in an iron-restricted medium, where most died. The yeast cells that thrived were assumed to have received the piece of Arabidopsis DNA that confers the ability to take up iron under iron-limited conditions. Researchers recovered the segment, and "read" its sequence, or genetic code.
The gene identified by the team encodes a protein that loops in and out of a cell's membrane, forming a portal through which iron may enter the cell. The researchers showed that this protein is only made in the roots of plants when the plants are starved for iron. The protein appears to draw the metal cadmium into cells as well. That property could prove useful to a new technique called phytoremediation, in which gene-altered plants are being used to remove toxic metals from contaminated soils. Cadmium is a metal pollutant associated with many toxic sites.
Cheryl L. Dybas, NSF, (703) 292-8070, email: firstname.lastname@example.org
Machi F. Dilworth, NSF, (703) 292-8470, email: email@example.com
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