Grasses' Guardian Gene Found
By Don Comis
January 29, 2008
The world's grasses might not have
survived long enough to evolve into the crops that feed the human raceas
well as provide a growing share of the world's energy needshad it not
been for one gene that has protected them against a deadly fungal pathogen for
more than 50 million years. These crops include wheat, corn, rice, rye, barley,
sorghum and switchgrass.
Collaborative research by
Scofield, a research geneticist in the Agricultural Research Service (ARS)
Production and Pest Control Research Unit in West Lafayette, Ind., and
Purdue University scientists Guri Johal
and Michael Zanis has proven that this gene, HM1, has been present in all
grasses since shortly after their origin and protects them from the fungus
Cochliobolus carbonum Race 1 (CCR1).
Johal isolated the HM1 gene in 1992 from mutants of corn in which the HM1
genes were not functional. CCR1 is a devastating pathogen in these mutant corn
lines, causing leaf blight, root and stalk rots, and ear mold. Fungal species
in the genus Cochliobolus were responsible for three of the worst crop
disease epidemics recorded in the 20th century, including the Southern corn
leaf blight of 1970 that devastated around 15 percent of the U.S. corn crop.
Johal also found that HM1 genes were present in other grass crops, raising the
question: Does HM1 also protect these other plants from CCR1?
Scofield and ARS colleagues developed a virus-induced gene silencing system
that switched off all HM1 genes in barleycausing it to become highly
susceptible to CCR1. This proved that the HM1 gene provides CCR1 resistance in
other grasses as well.
Thankfully, evolution generated the HM1 gene that provides highly effective
protection against CCR1 for these crops. The understanding of the first known
disease resistance gene that works across an entire taxonomic group holds
promise for scientists seeking to develop similar resistance in other crop
groups. Since mechanisms underlying broad disease resistance remain a mystery
in plant biology, this finding represents a major step in understanding an
important process in plant pathological research.
A paper on this research appears today in the Proceedings of the National Academy of
ARS is the U.S. Department of
Agriculture's chief scientific research agency.