Plants rely on a two-layered immune system to defend themselves against pathogens. The first system relies on extracellular receptors that recognize pathogen-associated molecular patterns (PAMPs) and thereby activates PAMP-triggered immunity (PTI). In the second system, plants use typically intracellular receptors to recognize pathogen virulence proteins (effectors) that are delivered into the plant cell and which have evolved to suppress PTI. This second line of defense is termed effector-triggered immunity (ETI). In this project, the molecular basis of PTI will be investigated using the interaction between tomato and the bacterial pathogen, Pseudomonas syringae pv. tomato (Pst). Pst delivers an effector, AvrPtoB, into the plant cell where it suppresses PTI and promotes bacterial virulence. In preliminary work, a possible host virulence target of AvrPtoB was identified and termed AvrPtoB-tomato-interacting protein 9 (Bti9). Bti9 has characteristics of a PAMP receptor with a putative extracellular region consisting of three LysM domains and an intracellular serine/threonine protein kinase. This project will test the hypothesis that Bti9 is a PAMP receptor that recognizes a bacterial cell wall component, peptidoglycan, and subsequently triggers intracellular signaling events via its kinase domain. Furthermore, the project seeks to determine whether the effector AvrPtoB interferes either with Bti9 kinase activity, the association of Bti9 with other host proteins, or possibly with Bti9 localization in the plant cell. This project investigates the function of Bti9, the structural aspects of the Bti9-AvrPtoB interaction, and the mechanism by which AvrPtoB may interfere with Bti9. The recent discovery of the importance of PTI to plant disease resistance has opened up new possibilities for the development of crop plants with broad, durable resistance to pathogens. This research focuses on a key aspect of PTI - a potentially novel bacterial-directed PAMP receptor and the mechanisms by which a pathogen effector has evolved to suppress its function. There are four areas where this research will have broad impact: 1) the PI and members of his lab will continue to improve a recently developed web-based module for High School teachers to introduce their students to plant immunity and to the social and economic consequences of plant diseases; 2) students from across the country will be trained as part of the NSF-supported Plant Genomics Summer Research Program hosted by the Boyce Thompson Institute; 3) the PI will continue to be active in several outreach efforts (past activities include leadership of an annual 'Field Day' that introduces summer interns to disease problems in New York agriculture); and 4) the PI has developed a new course for Cornell freshmen entitled: Innate Immunity in Plants, Flies, and Humans (BioG 1250) and results from this research will be incorporated into this course.
Intellectual Merit: This project investigated how a specific gene in tomato plays a role in the immune response against bacterial pathogens. Tomato is an important food crop and, in addition, it is a commonly used experimental plant to understand fundamental aspects of the plant immune system. This project showed that a tomato gene produces a protein that can detect specific disease-causing organisms and thereby activate defenses that kill the attacking organisms. The project also revealed how certain pathogens attempt to undermine the immune reponse. Specifically, it was found that a bacterial pathogen produces a protein that it injects into the plant cell where it binds to a tomato protein involved in immunity thereby undermining the plant defense response. Broader Impact: This research has increased our knowledge of how plants resist diseases and it provides the foundation for development of plants with increased disease resistance. This will reduce dependence on chemical pesticides, produce economic benefits for farmers, and provide food for US consumers that has fewer pesticide residues. This project trained two postdoctoral scientists both of whom are now faculty members at research universities. It also trained two PhD students and provided research experience to six undergraduate students. Training of plant scientists is important to the future food security and safety of the United States. Knowledge gained from this project was incorporated into two courses at Cornell University. This project took place at the Boyce Thompson Institute for Plant Research, which has a well-established Education and Outreach program to help instill scientific understanding through education of young students, high school teachers, and the general public.
