Hypernodulating Gene Found in
By boosting nitrogen fixation in soybeans and other legumes, farmers might
be able to cut down on the nitrogen fertilizer they apply to other field crops
grown in rotation.
Agricultural Research Service
scientists in the Plant Physiology Research Unit at Urbana, Illinois, have
identified a single gene that regulates hypernodulation in soybean root
systems. "We're now attempting to map the gene and produce a soybean
cultivar that has this trait and also produces high yields in the field,"
says plant physiologist James E. Harper.
On their roots, soybeans and other legumes create nodules that are tiny
homes for a type of bacteria that takes nitrogen from the air and enzymatically
converts it to ammonia that plants can use for growth and seed development.
Scientists speculate that the more nodules a plant produces, the more
nitrogen is left in plant tissues to be returned to the soil when the plant
dies and decomposes. This extra nitrogen is then available to a following crop.
Conventional soybean cultivars provide about 40 pounds of residual nitrogen
per acre. If hypernodulated soybean lines were to double the residual nitrogen
returned to the soil, this would provide over half of the nitrogen needs of
most corn varieties.
ARS scientists know that the chemical signal to regulate nodule formation in
the soybean root comes from above groundfrom young leavesduring the
first 4 weeks of plant growth. But they don't know what the chemical is or how
it signals plant roots to regulate nodule number.
"If we can learn what this chemical is and how it works, we can use the
information to regulate hypernodulation in soybean lines for commercial
use," says Harper.
Hypernodulated soybean lines can circumvent the natural nodule suppression
that exists in commercial cultivars. For example, a typical commercially
available soybean cultivar generates 70 to 200 nodules on its root system
during the first 4 weeks of growth. A hypernodulated mutant soybean generates
up to 1,000 during the same period.
Harper proved by using rooted leaf cuttings that the hypernodulation signal
comes from young soybean leaves. His research group also showed that the signal
is common between soybean and mung bean plants. They did this by grafting a
hypernodulated soybean shoot to a mung bean root, inducing hypernodulation on
the mung bean.
If scientists can identify the nodule control signal, they may be able to
induce hypernodulation in other legumes. By
Research Service Information Staff, 1815 North University Street, Peoria, IL
61604, phone (309) 681-6534.
James E. Harper is in the USDA-ARS
Plant Physiology and
Genetics Research Unit, University of Illinois, 331 ERML, 1201 W. Gregory,
Urbana, IL 61801; phone (217) 244-6670, fax (217) 333-6089.
"Hypernodulating Gene Found in Soybeans" was published in
the January 1998 issue of Agricultural Research magazine. Click here to see this issue's table of