A NAC transcription factor and a MADS-box protein antagonistically regulate sucrose accumulation in strawberry receptacles

Sugar accumulation during fruit ripening is an essential physiological change that influences fruit quality. While NAC transcription factors are recognized for their role in modulating strawberry (Fragaria × ananassa) fruit ripening, their specific contributions to sugar accumulation have remained largely unexplored. This study identified FvNAC073, a NAC transcription factor, as a key regulator that not only exhibits a gradual increase in gene expression during fruit ripening but also enhances the accumulation of sucrose. Further investigation showed that FvNAC073 positively regulates the expression of sucrose-6-phosphate synthase 1 (FvSPS1), a gene associated with sucrose synthesis, and negatively regulates sucrose synthase 2 (FvSUS2), which is involved in sucrose breakdown, through direct promoter binding. Additionally, we uncovered that FvCMB1L, a MADS-box protein, exhibits high gene expression levels at the premature fruit stage and acts to repress FvSPS1 while activating FvSUS2, thus negatively affecting sucrose accumulation. Notably, we demonstrated a competitive interaction between FvNAC073 and FvCMB1L in binding to the promoters of FvSPS1 and FvSUS2, resulting in antagonistic regulation of these genes. This intricate dynamic between FvCMB1L and FvNAC073 elucidates a mechanism for balancing sugar content during strawberry fruit development. Our findings offer insights into the complex regulatory network governing sucrose accumulation in strawberries, highlighting the potential for targeted genetic interventions to enhance fruit quality.