Sucrose synthase FaSS1 plays an important role in the regulation of strawberry fruit ripening

Sugar content and composition are critical to fruit development. Sucrose, a photosynthate unloaded to the fruit, is metabolized by sucrose synthase, which might play a dominant role in sucrose accumulation during strawberry fruit ripening. However, substantial evidence regarding the molecular mechanism underlying sucrose accumulation in strawberry fruit development is lacking. Here, a strawberry sucrose synthase gene, FaSS1, was cloned and identified. Its 2421-bp cDNA includes an intact open reading frame and encodes an 806 amino acid protein, in which sucrose synthase-related conserved domains were predicted by a homology analysis. Using tobacco rattle virus-induced gene silencing, the downregulation of FaSS1 transcripts significantly delayed fruit ripening, as evidenced by the changes of firmness, and soluble sugar and anthocyanin contents, as well as the transcripts of several ripening-related genes, including PE1, PL1, XYL2, CHS, CHI, and DFR. Furthermore, the mRNA expression level of FaSS1 was inhibited by abscisic acid or sucrose, but not by glucose after fruit disc incubation in vitro. In conclusion, FaSS1 plays an important role in the regulation of strawberry fruit ripening, and its expression could be inhibited by abscisic acid and sucrose.