Expression of genes involved in metabolism and transport of soluble carbohydrates during fruit ripening in two cultivars of Ficus carica L.

Fig trees are widely cultivated in the Mediterranean basin area where the fruit is appreciated by consumers for its nutritional characteristics. The taste and quality of fig fruits partially depend on the concentration and composition of soluble carbohydrates, and thereafter on the activity of enzymes and transporters of carbohydrate metabolism. We analysed the expression of 11 key genes of carbohydrate metabolism and of six genes encoding sugar transporters in fruits of two Italian cultivars, Dottato and Brogiotto. Most genes showed the expected expression pattern in the transition from unripe to ripe fruit. However, six out of 11 genes, encoding two sorbitol dehydrogenases, an alkaline/neutral invertase, an acidic invertase, and a hexokinase, and a phosphofructokinase, showed significant differences in transcripts level in unripe and/or ripe fruits between the two genotypes. Three out of six sugar transporter genes, encoding two sucrose transporters and one sorbitol transporter were up regulated in mature fruits of cv. Dottato. Glucose and fructose concentrations were higher than that of sucrose in the fruit of both cultivars. Sorbitol content was higher in Dottato than in Brogiotto fruits. In conclusion, the results suggested that differences in gene expression between the two cultivars do not affect the concentration of sucrose, glucose and fructose in mature fruits, while are likely responsible for the higher content of sorbitol observed in the ripe fruits of the cv. Dottato than in Brogiotto.