Abstract
Plants have evolved PAMP- and effector-triggered innate immunity to fight against pathogen attacks. Rac GTPase, RACK1, RAR1, SGT1 and Hsp90 are characterized as important components for plant defense signaling. However the relationship and molecular functions of these components are largely unknown. Here, we characterized a novel OsRac1 interacting protein, Sti1, which is a well-known component of steroid receptor complex in animal, as a key regulator for disease resistance. We found that suppression of Sti1 dampened resistance, while overexpression of Sti1 enhanced resistance in rice. Interestingly, Stil interacted with Hsp90 and plant PAMP receptor homologs (RLKs). Our results extend the existing tripartite interaction of RAR1, SGT1 and Hsp90 to a protein complex network, termed as "defensome", including Sti1, Rac1, and RLKs. Thus, we hypothesize Stil may function as an adaptor linking PAMP receptors and molecular switch (Rac1) together and contribute to PAMP-triggered innate immunity in rice.
