Genome-Wide Identification and Expression Analysis of bZIP Transcription Factors Under Salt Stress in Chrysanthemum

Chrysanthemum is one of the most important ornamental plants in the world. Its yield and quality are greatly affected by abiotic stress. The basic leucine zipper (bZIP) transcription factors play crucial roles in abiotic stress response; however, there has been no genome-wide investigation of the bZIP family in Chrysanthemums. Here, we identified 71 bZIP family proteins in the Chrysanthemum nankingense genome and classified them into 12 subgroups using phylogenetic analysis, including subgroups S, A, D, and G, and further performed a conserved motif, gene structure, and protein interaction network analysis for these subgroups. The results indicated that the members from the same subgroup often possess similar gene structures and motif organization, and the genes of the S subgroup are highly conservative during their evolution. The protein interaction network indicated that members of CnbZIP-S dominate the central position of the protein network. In addition, the expression of the CmbZIP genes in 'Jinba' was analyzed in root tissue via RNA-Seq after salt stress treatment. We found that 11 CmbZIP genes were down-regulated by salt treatment, and the bZIP-S genes, which were down-regulated, are more prevalent than other subgroups, indicating that the S subgroup genes may play an important role in the salt stress response in Chrysanthemum. Our research provides useful information for breeding new chrysanthemum cultivars with strong salt tolerance.