Transcription Factor CitERF16 Is Involved in Citrus Fruit Sucrose Accumulation by Activating CitSWEET11d

Abstract

Sugars are the primary products of photosynthesis and play an important role in plant growth and development. They contribute to sweetness and flavor of fleshy fruits and are pivotal to fruit quality, and their translocation and allocation are mainly dependent on sugar transporters. Genome-wide characterization of Satsuma mandarin identified eighteen <i>SWEET</i> family members that encode transporters which facilitate diffusion of sugar across cell membranes. Analysis of the expression profiles in tissues of mandarin fruit at different developmental stages showed that <i>CitSWEET11d</i> transcripts were significantly correlated with sucrose accumulation. Further studies indicated that overexpression of <i>CitSWEET11d</i> in citrus callus and tomato fruit showed a higher sucrose level compared to wild-type, suggesting that CitSWEET11d could enhance sucrose accumulation. In addition, we identified an ERF transcription factor CitERF16 by yeast one-hybrid screening assay which could directly bind to the DRE <i>cis</i>-element on the promoter of <i>CitSWEET11d</i>. Overexpression of <i>CitERF16</i> in citrus callus significantly induced <i>CitSWEET11d</i> expression and elevated sucrose content, suggesting that CitERF16 acts as a positive regulator to promote sucrose accumulation <i>via</i> trans-activation of <i>CitSWEET11d</i> expression.