WRKY70 interacting with RCY1 disease resistance protein is required for resistance to Cucumber mosaic virus in Arabidopsis thaliana

The gene RESISTANCE TO CMV(Y) (RCY1) encodes a coiled-coil (CC) nucleotide-binding (NB) leucine-rich repeat (LRR)-class resistance protein that confers resistance to a yellow strain of Cucumber mosaic virus [CMV(Y)] with developing the hypersensitive response (HR) cell death in virus-inoculated leaves of Arabidopsis thaliana. To understand the RCY1-mediated virus defense response, host protein that interacts with the CC and NB domains of RCY1 was isolated in a yeast two-hybrid system using the CC-NB domain fragment as bait. The WRKY70 transcription factor could reproducibly bind to the CC-NB domain fragment. This interaction between WRKY70 and the CC-NB domains was confirmed in a co-immunopurification experiment, suggesting that WRKY70 may function in RCY1-conferred resistance to CMV(Y). In CMV(Y)-inoculated leaves of wild-type plants carrying RCY1, virus multiplication was suppressed, and the level of WRKY70 and Pathogenesis-Related 1 (PR-1) transcripts clearly increased. On the other hand, in CMV(Y)-inoculated leaves of the RCY1-transformed wrky70-1 mutant lacking WRKY70 transcripts, virus coat protein accumulation increased significantly, and the induction of PR-1 expression in response to CMV(Y) was partially compromised. However, there was no significant difference in the degree of HR cell death between the wrky70-1 and wild-type plants carrying RCY1. These results indicate that WRKY70 may play a critical role in suppressing virus multiplication, but not in elaborating HR cell death, by directly interacting with the CC-NB domains of RCY1.