Role of the Mai1 Protein Kinase in Connecting Host Recognition of Pathogen Effectors to MAPK Signaling

Diseases of crop plants pose serious economic and environmental challenges to U.S. agriculture. The goal of this research is to generate knowledge that contributes to a comprehensive understanding of the plant immune system and enable innovative methods for the generation of crop plants that are naturally more resistant to pathogens. Such plants will reduce dependence on chemical pesticides, produce economic benefits for farmers, provide food for U.S. consumers that has fewer pesticide residues, and will contribute to the long-term improvement and sustainability of U.S. agriculture. The project focuses on the interaction of tomato with a bacterial pathogen, Pseudomonas syringae pv. tomato, which results in speck disease. This plant-pathogen interaction will be used to investigate how plants recognize specific pathogens and activate their immune systems in order to decrease the damage caused by diseases. The investigator will train a postdoctoral associate and a graduate student in cutting-edge molecular and biochemical methods used for the study of plant-pathogen interactions.<br/><br/>An important unanswered question in our understanding of plant immunity is how recognition of pathogen effectors by disease resistance (R) proteins is transmitted to mitogen-activated protein kinase (MAPK) cascades. These cascades consist of three sequentially activated protein kinases (MAPKKK-MAPKK-MAPK) and play a central role in immunity-related signal transduction leading ultimately to localized cell death and other defense responses that limit the infection process. A MAPKKK (hereafter M3Ka) was identified previously as a positive regulator of the immune response. Subsequently Mai1, a protein kinase with a tetratricopeptide repeat (TPR) domain, was discovered to be an interactor of M3Ka. Plants with reduced expression of Mai1 are unable to activate immune signaling in response to three R proteins. In this project multiple experimental approaches will be used to test the hypothesis that Mai1 is a molecular bridge between recognition of effectors by R proteins and MAPK signaling. The project objectives are to: 1) Develop plants with reduced expression of Mai1 and characterize the contribution of Mai1 to immunity; 2) Investigate the physical interaction of Mai1 with immunity-associated host proteins; 3) Characterize the possible role of post-translational modifications and the TPR domain in Mai1 activity. Mai1 provides an entry point into understanding how host recognition of pathogen effectors is transmitted to an important immunity-associated MAPK cascade and on to defense responses that limit disease. The proposed research will build on a well-understood plant-pathogen system to generate new insights into the molecular mechanisms underlying immunity-associated signal transduction in plants.