Mechanisms of plant immune receptor RPM1 and its associated proteins in disease resistance

Plants evolved an immune system to recognize specific pathogens, like animals. Recognition of pathogens in plants results in series of outputs such as generation of reactive oxygen species (ROS), cell wall lignification, and a type of programmed cell death (PCD) called the hypersensitive response (HR). Plant immune receptor proteins, disease resistance (R) proteins, are the necessity for this recognition process. The R proteins mediate the plant immune response through "direct" or "indirect" recognition of pathogen effector proteins. Our previous works proposed an "indirect" mode of recognition explaining that R proteins can monitor the host targets (guardees) by "guarding" them and sense the host targets modification by pathogen effector proteins. Here I present evidence that the Arabidopsis R protein RPM1 and its interacting protein RIN4 form protein complexes in the plant in the presence/absence of bacterial effector proteins implicating that the immune response regulated by R proteins can be controlled via immune complexes. I demonstrate data for RPM1 or RIN4 containing protein complexes by size exclusion chromatography (SEC). I also present data for putative RPM1 interactors by coimmunoprecipitation-coupled liquid chromatography (LC) / mass spectrometry (MS) / MS. With the known RPM1-interacting partner, RIN4, I defined the specific mechanisms of the RPM1-mediated immune response in Arabidopsis through the phosphorylation of the residue threonine 166 in RIN4 triggered by two evolutionarily unrelated bacterial effector proteins, AvrRpm1 and AvrB. Furthermore, I found that an important residue in RIN4, phenylalanine 169, is a key for physical interaction between RPM1 and RIN4 resultant in full accumulation and activation of RPM1 in Arabidopsis.