Genome-wide identification of MYB genes and analysis of their expression under different abiotic stress conditions in Stevia rebaudiana

The myeloblastosis (MYB) gene family is one of the largest families of regulators of gene expression, and its members control a variety of plant functions. Stevia glycosides (SGs) are the most important sugar substitutes and are isolated from Stevia rebaudiana. Recently, SrMYB1 was suggested to promote SG accumulation. However, few comprehensive studies are available on MYB family members associated with SG biosynthesis and stress responses in S. rebaudiana. In this study, 374 SrMYB genes from S. rebaudiana were discovered and sorted into three categories. The genomic localization and paralogs of the SrMYB genes revealed collinearity among these 374 genes on 11 chromosomes. Moreover, the protein motifs and gene structures of the SrMYB genes were determined. The cis-elements of the SrMYB promoter were involved in many aspects of plant growth and development. Moreover, RNA-seq data revealed that 35 SrMYB genes were potentially associated with SG biosynthesis in six Stevia lines ('023', '110', '11–14', 'GP', 'GX', and 'B1188') with different SG contents. qRT-PCR suggested that 20 SrMYB genes were widely expressed in various tissues; several of these genes were more highly expressed in leaves, which are the primary site of SG biosynthesis. In addition, these 20 SrMYB genes were differentially expressed in Stevia 'B1188' in response to polyethylene glycol (PEG), salinity, methyl jasmonate (MeJA), gibberellic acid (GA), salicylic acid (SA), and low-temperature stress, which are commonly used to promote SG production. Notably, the SrMYB genes Streb.3G004940.1, Streb.6G021840.1, Streb.11G030580.1, and Streb.1G039250.1 were obviously upregulated by various treatments. These findings provide further insight into the roles of SrMYB genes in controlling SG production and stress responses in S. rebaudiana.