NSF PR 96-28 - May 28, 1996
Media contact: |
Cheryl Dybas |
(703) 306-1070 |
Program contact: |
Machi Dilworth |
(703) 306-1423 |
This material is available primarily for archival purposes. Telephone
numbers or other contact information may be out of date; please see current
contact information at media
contacts.
Scientists Discover New Class of Genes
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.
|