Genome-wide in silico identification of glutathione S-transferase (GST) gene family members in fig (Ficus carica L.) and expression characteristics during fruit color development

Glutathione S-transferase (GSTs), a large and diverse group of multi-functional enzymes (EC 2.5.1.18), are associated with cellular detoxification, various biotic and abiotic stress responses, as well as secondary metabolites transportation. Here, 53 members of the FcGST gene family were screened from the genome database of fig (Ficus carica), which were further classified into five subfamilies, and the tau and phi were the major subfamilies. These genes were unevenly distributed over all the 13 chromosomes, and 12 tandem and one segmental duplication may contribute to this family expansion. Syntenic analysis revealed that FcGST shared closer genetic evolutionary origin relationship with species from the Ficus genus of the Moraceae family, such as F. microcarpa and F. hispida. The FcGST members of the same subfamily shared similar gene structure and motif distribution. The α helices were the chief structure element in predicted secondary and tertiary structure of FcGSTs proteins. GO and KEGG indicated that FcGSTs play multiple roles in glutathione metabolism and stress reactions as well as flavonoid metabolism. Predictive promoter analysis indicated that FcGSTs gene may be responsive to light, hormone, stress stimulation, development signaling, and regulated by MYB or WRKY. RNA-seq analysis showed that several FcGSTs that mainly expressed in the female flower tissue and peel during 'Purple-Peel' fig fruit development. Compared with 'Green Peel', FcGSTF1, and FcGSTU5/6/7 exhibited high expression abundance in the mature fruit purple peel. Additionally, results of phylogenetic sequences analysis, multiple sequences alignment, and anthocyanin content together showed that the expression changes of FcGSTF1, and FcGSTU5/6/7 may play crucial roles in fruit peel color alteration during fruit ripening. Our study provides a comprehensive overview of the GST gene family in fig, thus facilitating the further clarification of the molecular function and breeding utilization.