Functional Identification of the RiPFK2 Gene in Raspberry (Rubus idaeus L.) Demonstrates That It Enhances Fructose Content Inside Fruits

Fruit sweetness is a key trait that determines the quality of fresh raspberries and meets processing requirements. It is mainly regulated by the content of soluble sugars and organic acids. However, there is still a lack of systematic research on the molecular mechanisms of sugar accumulation during the development of raspberry fruits. This study used the raspberry variety ‘Caroline’ as material. By detecting changes in sugar content during fruit development and ripening, combined with transcriptomic analysis of related differentially expressed genes, it was found that the differentially expressed gene RiPFK2 was significantly upregulated during the period of rapid sugar accumulation in the fruit. We constructed an RiPFK2 overexpression vector and found that fructose content significantly increased in transgenic tomatoes and raspberries, indicating that this gene positively regulates fructose accumulation. This study is the first to reveal the positive regulatory role of PFK family members in fructose accumulation in raspberry fruits, providing a theoretical basis for improving raspberry fruit quality.