Genome-wide identification and expression of the lipoxygenase gene family in jujube (Ziziphus jujuba) in response to phytoplasma infection

Chinese jujube ( Ziziphus jujuba ) is an important fruit tree in China. Jujube witches' broom (JWB) disease, caused by JWB phytoplasma (‘ Candidatus phytoplasma ziziphi’), is the most devastating infectious disease of the jujube tree. Lipoxygenase (LOX) plays important roles in the jasmonic acid (JA) biosynthesis pathway and plant defense to biotic stresses. In this study, we identified 13 LOX genes in the jujube genome distributed on 5 chromosomes. The ZjLOX proteins were classified into two categories based on phylogenetic analysis. We tracked gene duplication events and found two sets of tandem repeats on chromosome 2. We predicted the promoters of the ZjLOXs using PlantCARE and found a large number of cis elements that may respond to phytohormones, light, and biological stresses. Transcriptomic, proteomic, and qRT-PCR expression analyses showed that ZjLOX02 , ZjLOX05 , ZjLOX06 and ZjLOX08 may play important roles in the interaction between jujube and phytoplasma. This study provides a foundation for better understanding both the molecular evolution of the jujube LOX gene family and the response of the ZjLOX genes to JWB phytoplasma infection.