Genome-Wide Identification of the APRR2 Gene Family and Rind Color Trait Analysis in Zucchini (Cucurbita pepo).

Abstract

Rind color is an important quality trait in zucchini (Cucurbita pepo). As a core transcription factor in plant pigment biosynthesis, APRR2 plays a conserved yet mechanistically diverse regulatory role in the formation of rind color in various vegetables. However, the APRR2 transcription factor regulates rind color but has not been systematically identified in C. pepo. In this study, 50 APRR2 genes were defined by the presence of the conserved REC domain verified. These genes were identified and found to be unevenly distributed across the 20 chromosomes, primarily expanded through tandem duplication events. Phylogenetic and structural analysis classified these genes into three distinct subgroups, all featuring the conserved REC domain essential for pigment regulation but exhibiting variations in motifs and intron-exon structures. Promoter analysis revealed abundant light-responsive, hormone-responsive and stress-responsive elements that may contribute to environmental adaptation and photomorphogenesis. Crucially, transcriptome analysis during rind development (0 and 10 days after pollination) in green (GR) and white (WR) rind lines demonstrated profound functional divergence. Expression clusters indicated temporal shifts in metabolism and enriched "circadian rhythm-plant" and "photosynthesis" pathways in WR at 0 DAP. Specific APRR2 genes were tightly correlated with rind color. qPCR validation of the 24 selected APRR2 genes classified them into four trend groups based on the direction of expression change at 10 DAP. In total, 14 genes were upregulated in both GR and WR, 6 were downregulated in both lines, 1 was upregulated in GR but downregulated in WR, and 3 were downregulated in GR but upregulated in WR. Furthermore, protein-protein interaction prediction and yeast two-hybrid (Y2H) assays detected a physical interaction in yeast between a core APRR2 protein and a bHLH62 transcription factor, suggesting a potential interaction that may be involved in rind color regulation, pending in planta validation. The study first identified the members of the APRR2 gene family in C. pepo and conducted a bioinformatics analysis on them. The study establishes the molecular basis of APRR2 function and offers valuable resources for breeding improved C. pepo varieties.