Genome-Wide Identification of the ZjWPR Gene Family in Chinese Jujube Provides Functional Insights into Its Response to Jujube Witches’ Broom

WPR (WEB1/PMI2-related) genes play a crucial role in regulating chloroplast movement and leaf coloration in plants. Previous studies have shown that these genes are implicated in leaf yellowing, both in Arabidopsis thaliana and in Paulownia fortunei following infection with Paulownia witches’ broom. To investigate the functions of the ZjWPR genes in jujube, bioinformatics methods were employed to identify the ZjWPR gene family in jujube, analyze their protein physicochemical properties, gene structure, evolutionary relationships, and cis-acting elements in this study. The results revealed that the ZjWPR gene family in jujube comprised 10 members. Phylogenetic analysis showed that WPR genes were divided into two classes, with ZjWPR genes distributed across three subgroups within Class II. Conserved motif analysis indicated that motif 2, motif 3, motif 7, and motif 8 were the most highly conserved and most genes exhibited similar structures. Cis-element analysis in their promoter suggested that ZjWPR genes were regulated by multiple hormones and were associated with stress responses such as low temperature and drought. Moreover, all ZjWPR genes contained light-responsive elements. Expression analysis of the ZjWPR gene family under Jujube Witches’ Broom (JWB) stress showed that ZjWPR4 and ZjWPR5 were significantly up-regulated in JWB-susceptible jujube cultivars following phytoplasma infection, whereas no significant changes were detected in JWB-resistant cultivars. Additionally, the expression levels of ZjWPR2, ZjWPR3, and ZjWPR6 were also altered in response to infection, suggesting their potential involvement in the response to JWB stress and the associated leaf chlorosis process. Moreover, transient overexpression of ZjWPR4 and ZjWPR5 in sour jujube leaves led to significant reductions, in critical photosynthetic parameters, including Fv/Fm, Fq′/Fm′, and ETR compared with WT, thereby reinforcing their functional contribution to JWB-associated leaf yellowing. This study provides valuable insights for further functional characterization of the ZjWPR gene family in mediating JWB-induced leaf yellowing and related metabolic pathways.