Blueberry fruit are rich in antioxidants and have become popular due to their numerous health benefits. In many fruits, a significant metabolic shift in carbon metabolism during fruit ripening leads to an increase in sugars, decrease in acids and accumulation of anthocyanins. The alterations in metabolic programs during fruit ripening in blueberry remain uncharacterized. Further, the role of ethylene in metabolic reprograming during blueberry ripening has not been studied. We quantified sugars, acids, anthocyanins and determined the expression of genes related to their metabolism. This study revealed that sucrose import into the fruit continues throughout ripening, with a corresponding increase in glucose and fructose. The transcript abundance of SUCROSE SYNTHASE and NEUTRAL INVERTASE was detected, suggesting sucrose catabolism in the cytosol. The high transcript abundance of VACUOLAR INVERTASE suggested that this gene plays a predominant role in sequestration of glucose and fructose in the vacuole. Malate and quinate were the major acids that displayed a decrease in concentration during ripening. The expression of MALATE DEHYDROGENASE and high transcript abundance of PHOSPHOENOLPYRUVATE CARBOXYKINASE suggested conversion of malate to phosphoenolpyruvate (PEP) during ripening. One of the potential fates of PEP, the generation of shikimate for anthocyanin production, was supported by the upregulation of multiple anthocyanin biosynthesis genes. Further, applications of ethephon and 1-aminocyclopropane-1-carboxylic acid, suggested that ethylene transiently stimulates sugar, acid and anthocyanin metabolism. This indicated ethylene is important for ripening initiation in blueberry. Overall, this study provided insights into metabolic programs, and the role of ethylene during blueberry ripening.
