Dissecting the molecular plant-pathogen interface using type III effector proteins

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As the global population continues to rise, bringing with it an increased demand for food, it will be crucial to engineer pest-resistant crops or develop robust, environmentally friendly disease control strategies to answer this demand effectively. The development of these disease control strategies requires extensive knowledge of host immune systems as well pathogen virulence strategies. Importantly, these two systems are interdependent and have shaped each other's evolutionary trajectory in a perpetual host-pathogen “arms race”. At the molecular level, the interface between pathogen virulence factors and host proteins is where this arms race is played out. As such, this interface represents a unique opportunity to investigate both the mechanisms of pathogen virulence as well as host resistance, and also to provide insights into the evolutionary pressures shaping these interactions. However, the molecular details of these interactions are limited and represent a major challenge of current studies in host-microbe interactions. The Desveaux lab uses a multidisciplinary approach to study host-microbe interactions using the Pseudomonas syringae / Arabidopsis thaliana model pathosystem. In particular, we are fascinated by a suite of proteins injected into host cells during the infection process that are essential for the virulence of many Gram negative bacterial pathogens including P. syringae. These proteins are injected using an evolutionarily conserved molecular syringe termed the type III secretion system. Inside host cells, type III secreted effectors target specific eukaryotic proteins in order to create a favourable environment for infection. However, type III secreted effectors can also betray the presence of the pathogen to its host since plants have evolved resistance proteins that detect specific type III effectors to induce a robust defence response that thwarts the infection process. As such, type III effectors represent invaluable probes to understand the molecular mechanisms of plant immunity as well as microbial virulence strategies. We are using two distinct families of P. syringae type III effectors to characterize the plant-microbe interface at the molecular and biochemical level in order to understand how pathogens cause disease and how plants have evolved to resist the infection process.