In order to resist infection, plants rely on their innate immune system to inhibit both pathogen entry and multiplication. Pathogen recognition by the plant innate immune system invokes a sophisticated signal transduction network that culminates in disease resistance.  The plant innate immune system can be divided into two branches based on the mode of pathogen recognition. In pattern-triggered immunity, plant receptors with extracellular domains recognize conserved molecular structures present in microbes. In effector-triggered immunity, primarily intracellular plant receptors recognize corresponding pathogen effector proteins. We are interested elucidating the signaling overlap between both branches of the plant innate immune system during bacterial infection. We use the plant protein RIN4, which can act to regulate both branches of plant immune responses, as a molecular probe to uncover important immune signaling networks.

Results/Conclusions

In order to identify novel proteins controlling immune signaling, we have purified components of the RIN4 protein complex from the model plant Arabidopsis in the presence and absence of pathogen stimulus. We found that one class of RIN4-associated proteins, the plasma membrane H+-ATPases AHA1 and AHA2, play a crucial role in resisting pathogen invasion. Our results indicate that RIN4 functions in concert with AHA to regulate stomatal apertures in order to block pathogen entry into the leaf. The discovery that RIN4 is a molecular link between immune signaling and stomatal movement provides an explanation for how this important defense regulator can act to control immunity at the level of pathogen invasion. We have also identified a protein kinase that can interact with and phosphorylate RIN4 during pathogen infection. Data will be presented on the importance of RIN4 phosphorylation for regulating plant immune responses.