Scientists Decipher Genome of Model Plant Pathogen
Rockville, MD - Scientists have deciphered and analyzed the genome of a model plant pathogen, Pseudomonas syringae pv. tomato, shedding new light on the molecular mechanisms by which the bacterium infects plants and adapts to thwart the host's defenses.
The microbe is the most widely used model for the study of plant pathogens. While the strain that was sequenced causes bacterial speck disease in tomato plants, other strains of P. syringae infect a wide variety of crops. The microbe is also closely related to other Pseudomonas species that cause diseases in humans and other animals.
'This genome sequence opens the door to the next level of research into diseases that infect plants,' says Robin Buell, who directed the P. syringae project at The Institute for Genomic Research (TIGR). 'Instead of trial-and-error exploration of plant pathogens, scientists now have the whole blueprint of a pathogen's genome, allowing for a more systematic examination of genetic targets.'
The research team that sequenced and analysed the P. syringae genome was led by Buell and by Alan Collmer of Cornell University's Department of Plant Pathology. The scientific paper was published online on August 19 in the Proceedings of the National Academy of Sciences (PNAS) and was scheduled for later publication in the PNAS print edition.The project was funded by the National Science Foundation's Plant Genome Research Program.
'This model organism will give researchers a leg up on learning about pathogenesis for many other bacteria,' says Jane Silverthorne, a program director in the NSF's plant genome research program. 'There is a lot to learn about how this bacterium infects tomatoes.'
Of the more than 5,500 genes in P. syringae, researchers identified 298 genes that appear to be involved in the microbe's virulence. Many of those virulence genes were close to mobile genetic elements, which play a role in the microbe's ability to adapt quickly to thwart changes in the host plant's immune system that aim to fend off infection. Mobile elements are small segments of DNA that can jump between organisms or their chromosomes.
'Pathogenesis is far more complex than anyone had dreamed,' says Collmer, noting that previous analysis had suggested that only a small number of the microbe's genes are involved in virulence. 'There is tremendous redundancy in the virulence system that we were able to uncover with the genome sequence.'
The bacterial strain that was sequenced is P. syringae pv. tomato DC3000. While that strain primarily infects tomato plants, causing a disease known as bacterial speck, it also infects the most important model plant Arabidopsis thaliana, or thale cress. For that reason, P. syringae and A. thaliana are widely used as a model pair for studies of how plants interact with pathogens.
But the P. syringae genome study may have wider uses and implications because the pathogen is closely related to other Pseudomonas species that infect humans and other animals. The genome analysis found 'a high degree of similarity' with the DNA sequences of two other sequenced pseudomonads: P. aeruginosa, which can infect humans and animals, and P. putida, which has potential uses for helping clean up environmental pollution.
TIGR was able to complete the genome sequencing project under budget, allowing the research team to use the remaining funds to sequence the genome of another strain of P. syringae that infects beans in Africa and other parts of the world. Because that strain does not infect the model plant A. thaliana, the twinned genome studies will provide scientists with potentially valuable comparisons between the closely related strains.
In addition to TIGR and Cornell, the research team includes scientists from the Boyce Thompson Institute for Plant Research, the University of Nebraska, the University of Missouri, Kansas State University, and the U.S. Department of Agriculture's Agricultural Research Service.