Comparative Transcriptomic Analysis Reveals Sugar Metabolism and Accumulation Mechanisms in Akebia trifoliata Fruits

Sugar composition is a critical determinant of fruit quality in fleshy fruits, influencing both organoleptic properties and nutritional value. Akebia trifoliata, an emerging fruit crop, possesses pulp rich in soluble sugars, vitamins, and polyphenols, making it suitable for fresh consumption, medicinal applications, and food processing. However, the molecular mechanisms governing sugar metabolism and accumulation in this species remain largely unexplored. We systematically evaluated the sugar content dynamics across different A. trifoliata germplasms and performed comparative transcriptomic analysis between high-sugar-accumulation (S4) and low-sugar-accumulation germplasms (S19) at three developmental stages (IM: the fruit is hard and immature; MA: the pulp remains firm, but the peel begins to soften and crack; and PM: the fruit is fully mature, and the pulp becomes shiny, translucent, soft, and edible). A total of 10,269 differentially expressed genes were identified with KEGG enrichment analysis, revealing significant enrichment in pathways directly associated with sugar biosynthesis. Through the analysis of weighted gene co-expression networks, a co-expression module significantly correlated with total sugar accumulation was identified, and qRT-PCR was used to verify that the expression levels of 29 candidate genes involved in carbohydrate synthesis were higher in the high-sugar-accumulation type than in the low-sugar-accumulation germplasm. These findings not only advance our understanding of the molecular basis of fruit quality development in this underutilized crop but also lay the foundation for the future breeding of A. trifoliata varieties with high-sugar greater nutritional value and processing qualities for the food industry.