Protein Kinase-Mediated Immunity In Arabidopsis And Nicotiana Benthamiana

Abstract

Protein kinases constitute a major component of the plant cellular signaling machinery, allowing plants to survive in diverse environments. However protein kinases are functionally redundant and are predominantly regulated by post-translational mechanisms, making them difficult to study using reverse genetics or transcriptomics. While the mechanisms by which some kinases perceive and respond to pathogens have been described, several important steps in signal transduction remain unstudied and an understanding of cross-talk between signaling pathways is lacking. By expanding our knowledge of protein kinases and their role in immunity, we can identify novel signaling components to target the pathways which are most likely to enhance stress tolerance. Here, we present studies outlining the role of select protein kinases in plant immunity using a proteomics approach. We first present a large-scale method for elucidating kinase interactions and target phosphorylation using protein microarrays. Next, we outline a functional study of pathogen effector-interacting kinases in Nicotiana benthamiana and demonstrate a role for the majority of these kinases in multiple immune pathways. This provides a novel view of the plant immune system where that different stimuli induce both shared and unique stress response pathways. We also observed a novel effector-specific immune response which is partially dependent on kinases. Finally, we describe the kinase activity and physiological role of the integrin-linked kinase 1 (ILK1) in ion transport, osmotic stress tolerance and immunity in Arabidopsis thaliana. Together with its interactor, the K+ transporter HAK5, ILK1 regulates plasma membrane depolarization, ion homeostasis and signaling in response to bacterial flagellin. Taken together, the findings presented here provide insights into the plant immune response. In particular, we demonstrated that disruption of select kinases can induce resistance to bacterial pathogens carrying specific effectors, indicating an undescribed form of immunity. We also identified the first molecular components involved in flagellin-induced membrane depolarization in mesophyll cells, indicating the potential importance of nutrient homeostasis in immune responses.