Abstract
BackgroundThe rice small GTPase OsRac1 is a molecular switch in rice innate immunity. The Receptor for Activated Kinase C-1 (RACK1) interacts with OsRac1 to suppress the growth of the rice blast fungus, Magnaporthe oryzae. RACK1 has two homologs in rice, RACK1A and RACK1B. Overexpressing RACK1A enhances resistance to the rice blast fungus. However, RACK1A downstream signals are largely unknown.ResultsHere, we report the identification of OsRap2.6, a transcription factor that interacts with RACK1A. We found a 94% similarity between the OsRap2.6 AP2 domain and Arabidopsis Rap2.6 (AtRap2.6). Bimolecular fluorescence complementation (BiFC) assays in rice protoplasts using tagged OsRap2.6 and RACK1A with the C-terminal and N-terminal fragments of Venus (Vc/Vn) indicated that OsRap2.6 and RACK1A interacted and localized in the nucleus and the cytoplasm. Moreover, OsRap2.6 and OsMAPK3/6 interacted in the nucleus and the cytoplasm. Expression of defense genes PAL1 and PBZ1 as well as OsRap2.6 was induced after chitin treatment. Disease resistance analysis using OsRap2.6 RNAi and overexpressing (Ox) plants infected with the rice blast fungus indicated that OsRap2.6 RNAi plants were highly susceptible, whereas OsRap2.6 Ox plants had an increased resistance to the compatible blast fungus.ConclusionsOsRap2.6 contributes to rice innate immunity through its interaction with RACK1A in compatible interactions.Electronic supplementary materialThe online version of this article (doi:10.1186/1939-8433-5-35) contains supplementary material, which is available to authorized users.
Highlights
The rice small GTPase OsRac1 is a molecular switch in rice innate immunity
RACK1A interacts with OsRap2.6 in yeast twohybrid assays Proteins that interacted with RACK1A in the rice cDNA library were screened in yeast two-hybrid (Y2H) assays
We found a strong interaction between RACK1A and OsRap2.6; there was no observed interaction in the (WT) or the (CA and dominant negative (DN)) OsRac1
Summary
The rice small GTPase OsRac is a molecular switch in rice innate immunity. The Receptor for Activated Kinase C-1 (RACK1) interacts with OsRac to suppress the growth of the rice blast fungus, Magnaporthe oryzae. Rice production is constrained by various diseases, the rice blast fungus, Magnaporthe oryzae being among the most prominent (Ribot et al 2008; Couch et al 2005; Valent and Chumley 1991). This fungus accounts for major losses in crops and grain yields (Wilson and Talbot 2009). ETI is the second line of defense that requires intracellular receptors of pathogen virulence molecules called effectors, whose recognition induces ETI and is triggered by resistance (R) proteins (Kawano et al 2010; Zipfel 2008; Dangl and Jones 2001)
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