Insights into sugar metabolism during bilberry (Vaccinium myrtillus L.) fruit development

Abstract

Bilberry fruit is regarded as one of the best natural sources of anthocyanins and iswidely explored for its health-beneficial compounds. Besides anthocyanins, one of themajor attributes that determine the berry quality is the accumulation of sugars thatprovide sweetness and flavor to ripening fruit. In this study, we have identified 25 sugarmetabolism-related genes in bilberry, including invertases (INVs), hexokinases (HKs),fructokinases (FKs), sucrose synthases (SSs), sucrose phosphate synthases (SPSs), andsucrose phosphate phosphatases (SPPs). The results indicate that isoforms of the identified genes are expressed differentially during berry development, suggesting special-ized functions. The highest sugar content was found in ripe berries, with fructose andglucose dominating accompanied by low sucrose amount. The related enzyme activi-ties during berry development and ripening were further analyzed to understand themolecular mechanism of sugar accumulation. The activity of INVs in the cell wall andvacuole increased toward ripe berries. Amylase activity involved in starch metabolismwas not detected in unripe berries but was found in ripe berries. Sucrose resynthesizing SS enzyme activity was detected upon early ripening and had the highestactivity in ripe berries. Interestingly, our transcriptome data showed that supplementalirradiation with red and blue light triggered upregulation of several sugar metabolism-related genes, including α- and β-amylases. Also, differential expression patterns inresponses to red and blue light were found across sucrose, galactose, and sugar-alcoholmetabolism. Our enzymological and transcriptional data provide new understanding ofthe bilberry fruit sugar metabolism having major effect on fruit quality (20) (PDF) Insights into sugar metabolism during bilberry ( Vaccinium myrtillus L.) fruit development.