Genome-Wide Identification, Characterization, and Expression Profiling of the ECERIFERUM (CER) Gene Family in Ziziphus jujube

The ECERIFERUM (CER) gene family plays an important role in wax biosynthesis. However, little is known about the CER gene family in jujube (Ziziphusjujuba Mill.). We identified 29 CER genes in the Z. jujuba genome and named them ZjCER1 to ZjCER29 according to their chromosomal locations. We then investigated the chemical characteristics, gene structures, and evolutionary relationships of these ZjCER genes. The genes were classified into three clades according to their phylogenetic relationship with Arabidopsis thaliana and Malus domestica. One pair of syntenic orthologous CER genes was matched between Z. jujuba and M. domestica. Analysis of conserved gene motifs revealed similar motifs within clades; 27 ZjCER genes had two or more introns. Twelve representative ZjCER genes showed different expression patterns in two Z. jujuba cultivars with contrasting cracking-resistant character. To further analyze the potential roles of ZjCER genes in response to various circumstances, we examined a 2.0 kb promoter region of the candidate ZjCER genes. All ZjCER genes except ZjCER28 shared a light-responsive element, and most shared hormone-related cis-elements. Our results provide rich resources for studying CER genes and potential clues for genetic improvement of jujube wax biosynthesis for improvement of cracking in Z. jujuba fruit.