Capsicum annuum WRKYb transcription factor that binds to the CaPR-10 promoter functions as a positive regulator in innate immunity upon TMV infection

In plant, some WRKY transcription factors are known to play an important role in the transcriptional reprogramming associated with the immune response. By using WRKY-domain-specific differential display procedure, we isolated CaWRKYb gene, which is rapidly induced during an incompatible interaction between hot pepper and Tobacco mosaic virus (TMV) pathotype P₀ infection. The recombinant CaWRKYb bound to the W box-containing CaPR-10 promoter probes efficiently and the specificity of binding was confirmed by mutant study and competition with cold oligonucleotides. Also, in GUS reporter activity assay using Arabidopsis protoplasts with the CaPR-10 promoter, GUS activity was increased in the presence of CaWRKYb. And CaWRKYb-knockdown plant showed reduced number of hypersensitive response local lesions upon TMV-P₀ infection. Furthermore, CaWRKYb-knockdown plant exhibited compromised resistance to TMV-P₀ by accumulating more TMV, apparently through decreased expression of CaPR-10, CaPR-1, and CaPR-5. These results suggest that CaWRKYb is involved as a positive transcription factor in defense-related signal transduction pathways in hot pepper.