The pathogenic effector PHYL1 JWB interacts with ZjCURT1A to mediate jujube witches' broom‐induced photosynthesis impairment of jujube trees

SUMMARY Photosynthesis impairment and the accompanying leaf yellowing represent a prominent and physiologically critical symptom of phytoplasma infection. However, the underlying molecular mechanisms remain poorly understood. In this study, we identified the Jujube Witches' Broom pathogenic effector PHYL1 JWB , which was previously reported to induce phyllody in jujube, as a key inducer of photosynthesis impairment. Overexpression of PHYL1 JWB in sour jujube and Arabidopsis thaliana disrupted photosynthesis by causing severe disorganization of chloroplast ultrastructure. PHYL1 JWB directly interacts with the integral thylakoid membrane protein ZjCURT1A and promotes its 26S proteasome‐dependent degradation independently of lysine ubiquitination, leading to disruption of thylakoid structure and photosynthetic dysfunction. The conserved two α‐helices of PHYL1 JWB and the C‐terminal segment of ZjCURT1A containing the thylakoid membrane curvature‐related CAAD motif are essential for their interaction. Together, these findings reveal that PHYL1 JWB impairs photosynthesis by disrupting chloroplast ultrastructural in addition to inducing phyllody, thereby contributing to abnormal plant growth. This work highlights the functional pleiotropy of pathogenic effectors and underscores the need to consider their impacts on multiple physiological processes in the context of phytoplasma pathogenicity.