<i>ClSWEET3a</i> mediates sucrose accumulation in wampee (<i>Clausena lansium</i>) fruit through transcriptional activation by ClbZIP3 and ClERF062

Soluble sugar is an important factor in determining fruit quality and flavor. In this study, the sugar accumulation mechanisms in wampee (<italic>Clausena lansium</italic>) fruits were investigated by using two cultivars—'Huami' (sweet) and 'Jinjixin' (sweet and sour)—at five developmental stages. Transcriptome analysis revealed a strong correlation between <italic>ClSWEET3a</italic> expression and total soluble sugar/sucrose content. Functional characterization demonstrated that ClSWEET3a, a plasma membrane-localized transporter, facilitates glucose and sucrose uptake in yeast. Silencing of <italic>ClSWEET3a</italic> in 'Jinjixin' fruits significantly decreased both sucrose and hexose levels, confirming its role in sugar accumulation. Furthermore, we identified two transcription factors (ClbZIP3 and ClERF062) that activate the <italic>ClSWEET3a</italic> promoter, with ClbZIP3 exhibiting stronger regulatory effects. Yeast one-hybrid assays confirmed their direct binding to the <italic>ClSWEET3a</italic> promoter. Our findings elucidate a molecular framework for sugar accumulation in wampee and provide insights for targeted breeding strategies to improve fruit quality.