Bacterial pathogenesis: Insights from a model plant-pathogen system

Infectious diseases caused by microbial pathogens are major problems in agriculture and human health. Understanding mechanisms of pathogenesis and immunity holds the key to the development of novel and sustainable strategies for long-term disease control. We have been using the Arabidopsis thaliana-Pseudomonas syringae pv. tomato (Pst) DC3000 pathosystem to uncover basic principles that underlie plant susceptibility to bacterial pathogens. Pst DC3000 is representative of a large number of bacterial pathogens that infect the above-ground parts (phyllosphere) of plants. During infection, this pathogen produces a battery of virulence factors to engage multiple host cell types (e.g., stomatal and mesophyll cells) and diverse host physical and chemical barriers. Its type III secretion system (T3SS) delivers about 30 “effector” proteins into the plant cell, whereas the phytotoxin coronatine mimics the active form of plant hormone jasmonate. Study of the molecular action of T3SS effectors and coronatine demonstrates the great utility of Pst DC3000 pathogenesis as a probe in the discovery of fundamental aspects of bacterial diseases, hormone signaling mechanisms, and stomatal immune function in plants. I will give an overview of our ongoing studies and a perspective of future research in this area.