Multi-Variety Transcriptomic Analysis Identifies Oxalate and L-Ascorbate Oxidation as Key Pathways Driving High Oxalate Levels in Sour-Type Star Fruit

Averrhoa carambola L. (family Oxalidaceae), known as star fruit, is a berry species found in tropical and subtropical regions, recognized for its unique crisp texture, high juiciness, and refreshing, slightly tangy flavor profile. A. carambola is known for its relatively high total oxalate content (fresh weight: 200–1840 mg/100 g), and excessive consumption is linked to toxicity, particularly in individuals with chronic kidney disease or other renal disorders. Therefore, understanding the mechanisms behind oxalate accumulation is crucial for developing effective strategies to manage oxalate levels in A. carambola . To our knowledge, this represents the first comprehensive transcriptomic investigation conducted across distinct fruit types of A. carambola . Results demonstrated that the downregulation of genes associated with oxalate oxidation contributes to the elevated oxalate content observed in sour-type A. carambola fruits. In addition, L-ascorbate concentration exhibits a positive correlation with oxalate levels across different varieties. These findings establish a foundational work for formulating rational and targeted strategies to regulate oxalate content in A. carambola , encompassing genetic improvement, optimized harvest timing, and carefully designed post-harvest management practices.