Phytoplasma Effector SJP8 Suppresses Host Immunity by Promoting the Degradation of ZjMYB15 and ZjMYB86-like to Perturb Jasmonic Acid and Hydrogen Peroxide Homeostasis in Jujube.

'Candidatus Phytoplasma ziziphi' infection causes severe damage to jujube (Ziziphus jujuba), inducing symptoms such as branch clustering, dwarfism, chlorosis and phyllody, leading to significant economic losses. However, the pathogenic mechanisms underlying jujube witches'-broom (JWB) disease remain largely unknown. In this study, we identified SJP8 as a key secreted effector protein of 'Ca. P. ziziphi'. Overexpression of SJP8 in jujube recapitulated the characteristic JWB-like symptoms, including dwarfism and leaf chlorosis. Transcriptome analysis revealed that SJP8 suppressed host immunity by downregulating jasmonic acid (JA)-related genes and upregulating hydrogen peroxide (H2O2)-related genes. SJP8 interacts with ZjMYB15 and ZjMYB86-like and promotes their degradation via the 26S proteasome pathway. Genetic transformation experiments demonstrated that ZjMYB15 and ZjMYB86-like positively regulate plant height and the expression of JA-related genes while repressing H2O2-associated genes. ZjMYB15 and ZjMYB86-like bind to their cognate motifs to activate ZjJAIPHX1 (encoding a jasmonate-induced protein homologue isoform X1) and ZjPOD43 (encoding peroxidase 43) transcription, thereby increasing JA content and decreasing H2O2 levels. Collectively, these results establish that the SJP8-ZjMYB15/ZjMYB86-like-ZjJAIPHX1/ZjPOD43 module suppresses plant immunity by perturbing JA and H2O2 homeostasis, thus both elucidating a phytoplasma effector's virulence strategy and providing molecular targets for breeding resistant jujube.