Deciphering the signaling cascade that facilitates the immune recognition of Pat-1 proteases of Clavibacter michiganensis in non-host plants

Plant resistance to pathogen attack is mediated through a complex system composed of immune receptors, co-receptors, and downstream signal transduction components that facilitate the recognition of various pathogen elicitors. Non-host recognition of specific pathogen avirulence protein elicitors often triggers strong immune responses that result in localized cell death at the site of infection known as the hypersensitive response (HR). Our group recently identified that the secreted serine proteases of the Chp family, Pat-1 and ChpG, of the tomato pathogen Clavibacter michiganensis elicit HR in the non-host plants tobacco and eggplant, respectively. We hypothesized that recognition of Chps in tobacco and eggplant is facilitated by transmembrane immune receptors. To test this, we used virus-induced gene silencing (VIGS) to silence global co-receptors and downstream components associated with HR-elicited by recognition by transmembrane receptors. Silencing of the global co-receptor SOBIR1, which is associated with transmitting the signal transduction of receptor-like proteins, reduced the HR induced by ChpG in eggplant but not the HR induced by Pat-1 in tobacco. On the other hand, silencing of EDS1, which serves as a global signaling component that act downstream to multiple immune receptors, significantly reduced the HR elicited by Pat-1 in tobacco but had a minor effect on the HR induced by ChpG in eggplant. Our data suggest that immune recognition of Chp proteases is distinct in tobacco and eggplant and relies on a different set of co-receptors and downstream components.