Role of MAPKKKa-Mediated Cell Death in Plant Disease Resistance and Susceptibility

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Role of MAPKKKa-mediated cell death in plant disease resistance and susceptibilityGregory Martin, Boyce Thompson Institute for Plant ResearchLocalized cell death occurs in leaves of both disease-resistant and disease-susceptible plants upon attack by disease-causing organisms. In resistant plants, rapid cell death (6 hrs) is referred to as the 'hypersensitive response' and is thought to inhibit further spread of the pathogen. In susceptible plants, host cell death occurs over the course of many days and manifests as disease symptoms referred to as 'specks', 'spots', or 'blights'. The extent to which host cell death is either a consequence or a cause of disease resistance and susceptibility is a central unresolved question in the study of plant pathogen interactions - in part because the molecular mechanisms underlying pathogenesis-related cell death are largely unknown. To investigate host cell death, this project will investigate both resistance and susceptibility in tomato to bacterial speck disease caused by Pseudomonas syringae pv. tomato. The central focus of the work will be a gene that encodes MAP kinase kinase kinase (MAPKKKa). When expression of this gene is interfered with the plant does not develop cell death during a disease-resistance response. Unexpectedly, it was found that silencing of MAPKKKa also interferes with cell death associated with bacterial speck disease. These observations indicate that the host plays an active role in promoting the formation of disease symptoms and that MAPKKKa acts as a molecular switch governing cell death associated with both resistance and susceptibility.This project aims to further define the molecular mechanisms underlying the role of MAPKKKa in host cell death. The objectives are: 1) Identify and characterize host proteins that function upstream of MAPKKKa; 2) Investigate the extent to which host disease resistance and susceptibility pathways share the same signaling components; and 3) Examine the role of MAPKKKa-mediated cell death in host responses to biotrophic and necrotrophic pathogens.There are three areas where this research will have broader impact: 1) Undergraduate students and high school students will be trained as part of the NSF-supported Plant Genomics Summer Research Program hosted by the Boyce Thompson Institute; 2) The PI and members of his lab will continue their involvement in several outreach programs including the New Visions high school program; and 3) Deeper understanding of the role of host cell death during pathogen attack will facilitate the development of new strategies of disease control thereby lessening dependence on pesticides.