A Sec-Dependent Effector from “Candidatus Phytoplasma ziziphi” Suppresses Plant Immunity and Contributes to Pathogenicity

Jujube witches' broom (JWB) disease, caused by <i>Candidatus</i> Phytoplasma ziziphi (<i>Ca</i>. P. ziziphi), severely threatens the production of Chinese jujube (<i>Ziziphus jujuba</i> Mill.). Emerging evidence highlights the critical role of phytoplasma-secreted effectors in pathogenesis, though few have been functionally characterized. Here, we identified a Sec-dependent effector, JWB790, from <i>Ca</i>. P. ziziphi, which was shown to suppress plant immunity. Through transient expression assays in <i>Nicotiana benthamiana</i>, pathogen inoculation assays, the generation of transgenic <i>Arabidopsis thaliana</i> plants, and RNA-seq-based transcriptomic profiling, we systematically investigated the virulence function of JWB790. Our findings revealed that JWB790 is highly expressed in JWB-infected tissues. The transient expression of <i>JWB790</i> in <i>N. benthamiana</i> suppressed BAX-induced cell death and H₂O₂ accumulation. Furthermore, the stable overexpression of <i>JWB790</i> in <i>A. thaliana</i> compromised disease resistance, accompanied by reduced H₂O₂ accumulation and callose deposition triggered by flg22. Additionally, the RNA-seq analysis of JWB790 transgenic <i>Arabidopsis</i> plants indicated that the overexpression of <i>JWB790</i> altered the expression of biotic stress-related genes. In summary, JWB790 is a virulence factor that suppresses plant immunity and promotes pathogen proliferation. These results advance our understanding of <i>Ca</i>. P. ziziphi pathogenesis.