Gene Identified as Key to
Sorghum’s Survival in Toxic Soils
Kenyan lines of sorghum displaying improved growth and yield on
field plots with acidic soils outside Moi University in Kenya.
Though many of the world’s acidic soils have aluminum
levels that are toxic to food plants, subsistence farmers often depend on these
soils to survive. ARS plant
physiologist Leon Kochian has been a part of a multinational effort to find a
gene in sorghum—a key food crop in Africa—to protect it against
aluminum toxicity in acidic soils.
“A lot of this work is targeted for developing
countries,” Kochian says. “We’re conducting basic research
with a global mission.”
Kochian leads the ARS Robert W. Holley Center for Agriculture
and Health, in Ithaca, New York. For this sorghum research, he collaborated
with his former Ph.D. student, Jurandir V. Magalhaes. Magalhaes is a scientist
with EMBRAPA Maize and Sorghum, a branch of the Brazilian Agricultural Research
Corporation (EMBRAPA), Brazil’s federal agricultural research agency.
The scientists knew that grasses like corn, rice, and wheat use
membrane transporters to protect against subsoil aluminum. When aluminum levels
are high, the transporters prompt a release of organic acid from the
tip—or apex—of the root. The organic acid bonds with the aluminum
ion and prevents entry of aluminum into the root.
In wheat, aluminum tolerance is regulated by a membrane
transporter encoded by the aluminum-tolerance gene ALTM1. The research
team found a gene in sorghum that protects it from soil aluminum via mechanisms
that closely parallel ALTM1’s activity.
Wheat’s ATLM1 gene encodes a transporter that
facilitates the release of malic acid. But in sorghum, the aluminum-tolerance
gene encodes a transporter that prompts the release of citric acid. The sorghum
transporter—dubbed SbMATE—is not related to the wheat transporter
and is a member of the “multidrug and toxic compound extrusion,” or
MATE, family of transporters.
Sorghum growing on an aluminum-toxic soil at the EMBRAPA Maize
and Sorghum research laboratory in Sete Lagoas, Brazil. Though the two middle
rows are sensitive to aluminum, the aluminum-tolerant row to the right shows 50
percent more shoot biomass.
The team found that the SbMATE gene is activated in
the roots of aluminum-tolerant sorghum only when aluminum is present in the
soil. Under these conditions, SbMATE is most highly expressed in the
first centimeter of the root tip, which allows for protection of the root tip
The researchers also saw that sorghum’s ability to
tolerate soil aluminum increased significantly the longer it was exposed to the
element. This finding correlates with both the increased release of organic
acids from the sorghum root over time and with the increased expression of
SbMATE that results from exposure to soil aluminum.
Taken together, these findings support the identification of
SbMATE as a new gene for aluminum tolerance. The researchers also
found that SbMATE is a major determinant of aluminum tolerance in
other sorghum accessions.
“I think we’ve found evidence for the co-evolution
of an important grass family trait by totally different genes,” Kochian
says. ARS and EMBRAPA are now engaged in collaborative projects with plant
breeders in Africa to develop aluminum-tolerant sorghum varieties for
cultivation in regional soils.
This work was recently published in the journal Nature
Genetics.—By Ann Perry,
Agricultural Research Service Information Staff.
This research is part of Plant Biological and Molecular
Processes, an ARS national program (#302) described on the World Wide Web at
Kochian is director of the
W. Holley Center for Agriculture and Health, Cornell University, Tower
Road, Ithaca, NY 14853-2901; phone (607) 255-2454, fax (607) 255-2739.
"Gene Identified as Key to Sorghum’s Survival in Toxic
Soils" was published in the
2008 issue of Agricultural Research magazine.