Genomic and expression analyses of glutathione S-transferase gene family in fig (Ficus carica L.) reveals candidate peel pigmentation genes

Glutathione S-transferases (GSTs) are multifunctional proteins that are essential in stress resistance, phytohormone response, and secondary metabolism. Here, we identified 42 GSTs in fig (Ficus carica L.) and used genomic information to rename them based on their chromosomal locations. Simultaneously, a constructed phylogenetic tree divided FcGSTs into five subfamilies, with Tau serving as the major subgroup. The distributions of conversed motifs and gene structures exhibited similar features in the same subfamilies. In total, six duplication events were identified in fig GSTs, and tandem duplication events fulfilled critical roles in the amplification of the Tau subfamily. Additionally, a synteny analysis showed that fig had similar evolutionary distances from Ficus hispida and Ficus macrocarpa. The cis-acting elements in promoter regions of FcGST genes were mainly related to light, hormone, stress, and plant growth and development. Furthermore, RNA-seq data revealed that quite a few FcGSTs had low expression levels during the developmental stages of ‘Purple peel’ fig. However, FcGSTF1 and FcGSTU5/6/7 are closely related to Transparent Testa 19 in Arabidopsis thaliana and GSTc in tea plants, respectively, which act as anthocyanin transporters. Their expression levels in color development of fig peels were correlated with anthocyanin biosynthesis. The findings provide a comprehensive understanding of the GST gene family and lay a foundation for future studies of anthocyanin transport in fig.