Genome-Wide Identification and Expression Analysis of bZIP Family Genes in <em>Stevia rebaudiana</em> Bertoni

The basic (region) leucine zippers (bZIPs) are evolutionarily conserved transcription factors widely distributed in eukaryotic organisms. In plants, they are not only involved in growth and development, defense and stress responses, and regulation of physiological processes, but also play a pivotal role in regulating secondary metabolism. To explore the function related to the bZIP gene family in Stevia rebaudiana Bertoni, we identified 105 SrbZIP genes at the genome-wide level and classified into 12 subfamilies using bioinformation methods. Analysis of physicochemical properties showed that the amino acid length readings ranged from 96 aa (SrbZIP13) to 704 aa (SrbZIP17), and the isoelectric point ranged from 4.64 (SrbZIP21) to 10.08 (SrbZIP101). The majority of these proteins (94.29%) were localized in the nucleus. Three main classes of cis-acting elements found in the SrbZIP promoter regions, including development-related elements (CAT-box), defense and stress-responsive elements (LTR/ARE/MBS), and phytohormone respon- sive elements (ABRE/TGACG-mitif/TCA-element). Through protein-protein interac- tion network of 105 SrbZIP proteins, SrbZIP proteins were mainly classified into four major categories: ABF2/ABF4/ABI5 (SrbZIP51/SrbZIP38/SrbZIP7), involved in phy- tohormone signaling, GBF1/GBF3/GBF4 (SrbZIP29/SrbZIP63/SrbZIP60) involved in environmental signaling, AREB3 (SrbZIP88), PAN (SrbZIP12), TGA1 (SrbZIP69), TGA4 (SrbZIP82), TGA7 (SrbZIP31), TGA9 (SrbZIP95), TGA10 (SrbZIP79) and HY5 (SrbZIP96) involved in cryptochrome signaling, and FD (SrbZIP23, SrbZIP24, SrbZIP47, SrbZIP67, SrbZIP68, SrbZIP71, SrbZIP72) promoted flowering. The transcriptomic data showed that SrbZIP genes differentially expressed in six S. rebaudiana cultivars (‘023’, ‘110’, ‘1188’, ‘11-14’, ‘GP’ and ‘GX’). Moreover, the expression levels of selected 15 SrbZIP genes in response to light, abiotic stress (low temperature, salt and drought), phytohormones (methyl jasmonate, gibberellic acid and salicylic acid) treatment and in different tissues were analyzed utilizing qRT-PCR. Six SrbZIP (SrbZIP54, SrbZIP63, SrbZIP32, SrbZIP45, SrbZIP60 and SrbZIP9) genes were further identified to be highly induced by factors affecting glycoside synthesis. Among them, three SrbZIP genes (SrbZIP54, SrbZIP63 and SrbZIP32) were predicted to be related to stress-responsive terpenoid synthesis in S. rebaudiana. The protein-protein interaction network expanded the potential functions of SrbZIP genes. This study firstly provided the comprehensive genome-wide report of the SrbZIP gene family, laying a foundation for further research on evolution, function and regulatory role of bZIP gene family in terpenoid synthesis in S. rebaudiana.