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Rhodococcus is a genus of Gram-positive bacteria in the Actinobacteria phylum. Members of R. fascians and related sister species can infect and cause disease to a wide range of plants. The disease symptoms include leafy gall-like structures and other deformities. Current models suggest these pathogenic organisms synthesize and secrete plant hormones to cause dysregulation. We are investigating the mechanism and evolution of Rhodococcus pathogenicity. We have sequenced the genome of 20 phytopathogenic Rhodococcus strains and analyzed the genetic history of several known virulence loci putatively involved in manipulating cytokinin levels. If you have diseased plant tissues or a collection of R. fascians, please let us know! Please follow the link to the OSU Plant Clinic for more information on diagnosis and management.



Agrobacterium tumefaciens

Gaillardia 04-1946 Agro.JPGA. tumefaciens is a Gram-negative bacterial pathogen. Like R. fascians, it can infect a wide range of plants and upon doing so, also causes growth deformaties. However, A. tumefaciens promotes hormone dysregulation in a decidedly different manner than R. fascians. A. tumefaciens coerces plants to overproduce hormones by genetically modifying its host. In doing so, the pathogen also modifies host plants to synthesize opines, a carbon source that the bacteria can catabolize. We are generating whole genome sequences for hundreds of isolates collected from across the world and from infected plants, collected from across the United States. Our goal is to model the evolutionary history, construct a phylogenetic framework for these bacteria, and model the population structure of pathogenic Agrobacteria. If you have diseased plant tissues or a collection of Agrobacterium, please let us know! Please follow the link to the OSU Plant Clinic for more information on diagnosis and management.




Pseudomonas syringae

P. syringae is a Gram-negative bacterial pathogen. Collectively, members of this species can also infect a number of plant hosts but individually, its members tend to have restricted host ranges. P. syringae relies on a molecular syringe, called a type III secretion system to inject proteins, called type III effector proteins, directy into host cells. Inside the host cell, type III effectors function to suppress plant immunity and also to help promote the release of nutrients. We authored a review paper on bacterial secretion systems. In this review, we highlighted seven secretion systems that are used by various plant-associated bacteria. A fair amount of the review was devoted to the type III secretion system and its effector proteins.


Other notable bacterial species of interest

Our interest in type III effectors led us to study their use by mutualistic, nitrogen-fixing rhizobia.

We are also working on other Gram-positive bacterial pathogens of plants. Our work on Rhodococcus helped us expand our interests to include other Gram-positive phytopathogens. This group of bacteria has many fascinating and economically important members. But as we quickly learned, they are exceptionally challenging to manipulate!