Ithaca, New York
August 15, 2003
The complete genome
sequence of a leading bacterial plant pathogen offers new ways
to stave off agricultural loss and perhaps foil animal or human
infection, says a Cornell University researcher.
According to Alan Collmer, Cornell professor of plant pathology,
the sequencing (that is, determining the base sequence of each
of the ordered DNA fragments in the genome) could help farmers
repress
tomato speck and other plant diseases. Medical researchers could
be aided in comparing a related bacterium that causes fatal lung
infections in cystic fibrosis patients. And environmentalists
could be provided with a new tool in understanding how another
related bacterium can live in soil and dine on toxic waste.
The sequencing of Pseudomonas syringae (strain DC3000) is
reported on the Web by scientists from Cornell
and The Institute for Genomic Research (TIGR) in the
Proceedings
of the National Academy of Science (PNAS Online Early Edition).
The P. syringae genome will be particularly helpful to
scientists studying P. aeruginosa, a bacterial cousin blamed for
chronic and fatal lung infections in cystic fibrosis patients
and acute infections of cancer and burn patients, says Collmer,
who is principal investigator on the project. Comparisons of the
genomes, he says, will help researchers understand how these
bacteria have adapted to their hosts and could reveal weak
points to target with new therapies.
"Understanding this genome connects us to a larger world of
bacterial pathogens," says Collmer. "Pseudomonas syringae
(pronounced soo-dough-MOAN-iss seer-INN-gee) has become a
premier model for studying plant diseases. The genome reveals
how complex the jigsaw puzzle of pathogenesis is. It puts all of
the pieces on the table, it shows us that many parts of the
puzzle are the same for plant and animal pathogens, and it
enables scientists to put the pieces together more efficiently."
The project was funded by the National Science Foundation Plant
Genome Research Program. C. Robin Buell, a biologist with TIGR,
directed the complete sequencing of the genome. Many bacteria
that are animal and plant pathogens -- including the plague
bacterium Yesinia pestis -- inject virulence proteins into
healthy host cells using what is called a "type III secretion
system." The researchers discovered the genes encoding more than
35 injected-virulence proteins, more than for any other known
pathogen, through collaboration with Cornell Theory Center
computational biologists Samuel Cartinhour and David Schneider
of the U.S. Department of Agriculture's (USDA) Agricultural
Research Service.
P. syringae is a major agricultural pathogen, causing bacterial
speck on tomatoes. It produces black lesions, often with a
discrete yellow halo that can appear on the plant leaves and
cause them to curl. In 1977-78 the bacteria caused serious
losses to the winter tomato crop in southern Florida. Cool,
moist environmental conditions contributed to the development of
the disease, and it had established itself as a major problem,
according to Thomas A. Zitter, Cornell professor of plant
pathology.
In the years before 1977, growers had sprayed a copper-based
pesticide to ward off bacterial speck, but the pathogen became
resistant to the copper, rendering the pesticide virtually
useless.
Natural resistance genes have been bred into certain tomato
plants to control the disease. Gregory Martin, Cornell professor
of plant pathology and a scientist at the Boyce Thompson
Institute for Plant
Research (an independent research facility on Cornell's campus),
and Steven Tanksley, Cornell professor of plant breeding, cloned
the first such resistance gene in 1993. The gene, Pto, enables
tomato plants to recognize P. syringae and turn on strong
defenses.
Over time, however, variants of the pathogen have arisen that
can evade detection. Using information from the sequencing of P.
syringae, Martin, a member of the sequencing team, and other
researchers are now exploring how pathogens adapt to plant
defenses.
Other researchers involved in the sequencing research were James
R. Alfano, University of Nebraska-Lincoln; Arun K. Chatterjee,
University of Missouri; Terrence P. Delaney, Cornell assistant
professor of plant pathology; Sondra G. Lazarowitz, Cornell
professor of plant pathology; and Xiaoyan Tang, Kansas State
University.
Related World Wide Web sites:
The following sites
provide additional information on this news release. They are
not part of the Cornell University and the university has no
control over their content or availability.
Proceedings of the National Academy of Sciences:
http://www.pnas.org
The Institute for Genomic Research:
http://www.tigr.org
The National Science Foundation:
http://www.nsf.gov
See also:
Genome sequence for tomato-infecting microbe
may show how bacteria adapt to plant defenses
Abstract and online
access to the complete paper:
http://www.pnas.org/cgi/content/abstract/1731982100v1?etoc
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