dlo-miR827 Negatively Regulates Sucrose Accumulation by Targeting DlSPS1 in Longan ( Dimocarpus longan Lour.) Fruit

Sucrose is a key determinant of sweetness and flavor in longan fruits, while the regulatory role of microRNAs (miRNAs) in its accumulation is not well understood. In this study, small RNA sequencing of high-sucrose cultivar "Songfengben" (SFB) and low-sucrose cultivar "Qingkebaoyuan" (QKBY) identified 402 miRNAs, including 115 differentially expressed miRNAs (DEMs). Novel-miR-309 (rename dlo-miR827) was predicted to target DlSPS1, a key sucrose biosynthesis gene. Dual-luciferase assays confirmed that dlo-miR827 directly suppressed DlSPS1 expression. Transient overexpression of the dlo-miR827 precursor (dlo-MIR827) in "Shixia" longan fruit and stable overexpression in Arabidopsis thaliana significantly reduced sucrose accumulation and downregulated sucrose phosphate synthase homologue expression. These results demonstrate that dlo-miR827 negatively regulates the sucrose content by targeting DlSPS1. Our findings reveal a novel miRNA-mediated mechanism controlling sucrose accumulation in longan, providing a potential target for molecular breeding to enhance fruit quality.