4.2 WRKY33 functions as a positive regulator in the AR156-triggered ISR against broad-spectrum pathogens
Plant transcription factors play an essential role in plant growth and development, morphogenesis, and stress resistance responses. It has been widely reported that WRKY transcription factors are involved in plant immunity. SlWRKY8 promotes resistance to Pst DC3000 and enhances tolerance to drought (Gao et al., 2020). Overexpression ofAtWRKY48 confers resistance to Pst DC3000 inArabidopsis (Xing et al., 2008). AtWRKY70 and AtWRKY11 were essential for AR156 elicited ISR response to Pst DC3000 (Jiang et al., 2015). It was shown that the WRKY33 transcription factor is a dominant regulator of SAR triggered by local Pst DC3000 invasion, while the SAR triggered by local invasion of Pst DC3000 was depleted in the wrky33 mutant (Wang et al., 2018). In the current study, we identified WRKY33 transcription factor upregulation by AR156 treatment at different time points. Moreover, WRKY33 was required for AR156-mediated accumulation of camalexin during pathogenic infection. Concurrently, AR156-induced CYP71A13 and PAD3 upregulation was significantly attenuated in the wrky33 mutant, which fully illustrated that WRKY33 was critical for AR156-mediated synthesis of camalexin upon pathogens invasion (Figure 4). AR156 was found with a diminished function in inducing resistance to different pathogens. As the result is shown in Figure 5 compared to the control inoculated withP. capsici and B. cinerea only, the biomass ofP. capsici and B. cinerea in AR156 pretreated wrky33 mutant plants were quite similar. AR156-induced ISR resistance to Pst DC3000 was significantly attenuated in the wrky33 mutant. In parallel, we found that Col-0 and wrky33 mutants displayed similar susceptibility to pathogens when inoculated only with P. capsiciand Pst DC3000, which was in line with the results of previous studies (Zheng et al., 2006).