Molecular Mechanism of ZjWRKY40-zju-miR157 Module Regulating Phytoplasma Tolerance in Jujube

Phytoplasma ('Candidatus Phytoplasma'), a bacterial pathogen, is a significant plant health concern worldwide, resulting in substantial economic losses. In jujube (Ziziphus jujuba), it is often referred to as a cancer-like disease that can destroy the whole plant and cause great economic loss, posing serious challenges to jujube's sustainable development. Here, the phytoplasma tolerance mechanism in jujube was revealed by the identification of a highly phytoplasma-tolerant jujube genotype. Integrated transcriptomic and metabolomic analyses were conducted to compare a phytoplasma-susceptible genotype Fuxiang with a tolerant genotype T13. The results revealed that the ZjWRKY40 gene was significantly upregulated in T13 about 3-fold at the third development stage, suggesting its key role in mediating phytoplasma tolerance. A phytoplasma effector SJP4_JWB was identified and shown to interact with ZjWRKY40 by yeast two-hybrid and co-immunoprecipitation methods. In addition, ZjWRKY40 was found to bind to the promoter of zju-miR157, thereby regulating its expression. Moreover, zju-miR157 targeted ZjSPL3 and negatively affected the phytoplasma tolerance by downregulating ZjSPL3 expression. Together, these findings outline a regulatory network involving SJP4_JWB-ZjWRKY40-zju-miR157, which provides important insights into the molecular mechanism of the phytoplasma tolerance in jujube and lays a foundation for developing tolerant genotypes through molecular breeding.