CC-NBS-LRR-Type R Proteins for Rice Blast Commonly Interact with Specific WRKY Transcription Factors

Rice blast resistance caused by Resistance (R) genes, most of which encode coiled-coil (CC), nucleotide-binding (NB), and leucine-rich-repeat (LRR) domains, is race-specific. Panicle blast 1 (Pb1) is a panicle blast resistance gene that confers a durable non-race-specific blast resistance to rice. Despite being non-R, Pb1 also encodes a CC-NB-LRR protein. Pb1 specifically interacts with rice WRKY45, a transcription factor (TF) in the rice salicylic acid signaling pathway, through its CC domain, and that this interaction is important for the blast resistance conferred by Pb1. Additionally, barley MLA10, an R protein for Blumeria graminis, specifically interacts with HvWRKY1/2. Here, we investigated whether the blast resistance between conferred by R genes and non-R Pb1 genes is mediated by their interaction with WRKY TFs. We performed targeted yeast two-hybrid and glutathione S-transferase (GST)-pull-down assays, which showed that all the five rice R proteins of the CC-NB-LRR type tested, Pi36, Pib, Pita, Pit, and Piz-t, interacted with WRKY45 and WRKY66 through their CC domains. However, elicitor-triggered immunity due to these R genes was not affected by the knockdown of these WRKY genes. The results suggest that R proteins can potentially transduce defense signals by interacting with WRKY TFs but the potentials are masked by HR-mediated elicitor-triggered immunity responses.