Genome-wide identification and functional characterization of six ERD6-like genes involved in soluble sugar accumulation and response to drought in peach (Prunus persica)

Soluble sugars are key determinants of fruit quality, contributing to the desirable flavors of fruit crops such as peach. Our previous research identified PpERDL16 (early response to dehydration 6-like) as a negative regulator of fructose content in peach fruits. The current study identifies six ERD-like genes and classifies them into four subfamilies through bioinformatics and gene expression analyses. All six genes contain sugar transporter domains and are localized to the tonoplast, confirmed by subcellular localization assays in tobacco. The expression analysis undertaken during fruit development revealed that the genes PpERDL6-1 (previously as PpERDL16), PpERDL6-2 and PpERDL6-3 were highly expressed during the early stages of fruit ripening, with PpERDL6-1 showing a marked downregulation during the late ripening stage. Functional assays demonstrated functional divergence for these genes in sugar modulation: transient overexpression of PpERDL6-1 significantly reduced fructose and glucose levels, whereas overexpression of PpERDL6-2 specifically increased glucose levels in mesocarp slices. Additionally, overexpression of PpERDL6-3, PpERDL6-4, and PpERDL6-6 led to enhanced fructose accumulation. Further, Promoter motif analysis indicated that all six ERD6-like genes are responsive to light and hormonal stimuli related to abiotic stress. Under drought treatment, soluble sugars (glucose, fructose and sucrose) accumulated significantly, and expression of all six genes was fluctuated. In conclusion, our findings highlight the pivotal roles of the ERD6-like gene family in regulating soluble sugar accumulation, suggesting their involvement in the coordination of peach fruit sweetness and stress response. This study offers novel insights into the molecular mechanisms that underpin fruit quality improvement under abiotic stress conditions.