Integrative analysis of the transcriptome and starch/sugar content revealed changes in starch and sugar metabolism in durian (Durio zibethinus L.) fruit ripening

Carbohydrates are essential for human nutrition and are derived from a wide range of plants, including economically important fruit crops such as durian (Durio zibethinus L.), which is extensively cultivated across Southeast Asia. Despite the importance of starch and sugars in fruit development and flavor formation, their underlying metabolic pathways in durians remain largely unexplored. To address this knowledge gap, we performed a comprehensive reference-based transcriptomic analysis accompanied by the quantification of starch and sugar dynamics throughout the developmental and ripening stages of the Monthong durian cultivar. A substantial accumulation of starch during fruit development paralleled with the upregulation of key starch biosynthetic genes, including DzAPL1, DzAPS2, DzSS1, DzSBE1, DzSBE2, DzISA1, and DzISA2. In contrast, a decline in starch content during ripening was negatively correlated with the increased expression of starch degradation genes such as DzAMY, DzAMY3, and DzBAM1. Sucrose was the predominant sugar in durian pulp across all stages, whereas fructose, glucose, and maltose were presented at significantly lower levels. Within the durian pulp, DzSPS1 and DzSPS4 were the key sucrose biosynthetic genes, whereas DzSuSy and DzINV were key contributors to sucrose degradation. Additionally, DzSUC2, DzSWEET10, and DzN3 were the major genes involved in sucrose uptake and transport. Notably, sucrose content and the expression patterns of DzSUC2 and DzSWEET10 were similar in the early-harvesting cultivar Chanee and the late-harvesting cultivar Monthong, suggesting a conserved regulatory mechanism. Collectively, these findings provide novel insights into the complex regulatory networks governing starch and sugar metabolism in durian.