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Jeff Chang
Assistant Professor, Botany and Plant Pathology
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RESEARCH:
My interests are in understanding the interactions between bacteria and plants. Pathogens and symbionts use a common mechanism to facilitate their interactions with plants. Both deliver type III effector proteins directly into host cell through a type III secretion system (TTSS). This suggests that despite their drastically different lifestyles, they perturb similar host pathways.
Pseudomonas syringae is a model pathogen of plants. P. syringae must deliver type III effector proteins in order to cause disease; strains incapable of doing so are avirulent. Thus type III effector proteins confer positive functions to pathogens. Ironically, some type III effectors also have negative roles. They can elicit host resistance responses and render the bacterium avirulent. Many strains of P. syringae have been screened for their collections of type III effectors. Yet, their functions remain elusive. I am interested in understanding how one strain uses its arsenal of type III effector proteins to cause disease on its compatible host. I am using bioinformatic and proteomic approaches to determine how type III effectors function and to identify their corresponding host targets. This will inform on the dichotomous interactions between pathogen and host: 1) the mechanism by which bacteria render plants susceptible to disease, and 2) the resistance mechanisms that plants use to combat pathogens.
Species of Rhizobia form symbiotic relationships with legumes. They fix atmospheric nitrogen in exchange for carbon sources. Genes encoding for TTSS have been identified in some strains. Its function in symbiosis is a mystery. It is however clear that like P. syringae, the TTSS and the type III effectors Rhizobia deliver also have positive and negative roles in defining host range. The collection of type III effectors has not been identified from even one strain of Rhizobia. I am using high-throughput genomics methods to identify type III effectors of Rhizobia. I am interested in understanding how type III effectors contribute towards symbisis. This study provides the means to extending host range of Rhizobia.