GST family genes in jujube actively respond to phytoplasma infection

Jujube witches' broom (JWB) caused by phytoplasma has a severely negative effect on multiple metabolisms in jujube. The GST gene family in plants participates in the regulation of a variety of biotic and abiotic stresses. This study aims to identify and reveal the changes in the jujube GST gene family in response to phytoplasma infection. Here, 70 ZjGSTs were identified in the jujube genome and divided into 8 classes. Among them, the Tau-class, including 44 genes, was the largest. Phylogenetic analysis indicated that Tau-class genes were highly conserved among species, such as Arabidopsis, cotton, chickpea, and rice. Through chromosome location analysis, 37.1% of genes were clustered, and 8 of 9 gene clusters were composed of Tau class members. Through RT-PCR, qRT-PCR and enzyme activity detection, the results showed that the expression of half (20/40) of the tested ZjGSTs was inhibited by phytoplasma infection in field and tissue culture conditions, and GST activity was also significantly reduced. In the resistant and susceptible varieties under phytoplasma infection, ZjGSTU49-ZjGSTU54 in the cluster Ⅳ showed opposite expression patterns, which may be due to functional divergence during evolution. Some upregulated genes (ZjGSTU45, ZjGSTU49, ZjGSTU59, and ZjGSTU70) might be involved in the process of jujube against JWB. The yeast two-hybrid results showed that all 6 Tau-class proteins tested could form homodimers or heterodimers. Overall, the comprehensive analysis of the jujube GST gene family revealed that ZjGSTs responded actively to phytoplasma infection. Furthermore, some screened genes (ZjGSTU24, ZjGSTU49-52, ZjGSTU70, and ZjDHAR10) will contribute to further functional studies of jujube-phytoplasma interactions.