Pomegranate (Punica granatum L.) is an ancient fruit crop that has been cultivated worldwide and is known for its attractive appearance and functional metabolites. Fruit color is an important index of fruit quality, but the color formation pattern in the peel of evergreen pomegranate and the relevant molecular mechanism is still unknown. In this study, the contents of pigments including anthocyanins, carotenoids, and chlorophyll in the peel of ‘Danruo No. 1’ pomegranate fruit during three developmental stages were measured, and RNA-seq was conducted to screen key genes regulating fruit color formation. The results show that pomegranate fruit turned from green to red during development, with a dramatic increase in a* value, indicating redness and anthocyanins concentration, and a decrease of chlorophyll content. Moreover, carotenoids exhibited a decrease–increase accumulation pattern. Through RNA-seq, totals of 30, 18, and 17 structural genes related to anthocyanin biosynthesis, carotenoid biosynthesis and chlorophyll metabolism were identified from differentially expressed genes (DEGs), respectively. Transcription factors (TFs) such as MYB, bHLH, WRKY and AP2/ERF were identified as key candidates regulating pigment metabolism by K-means analysis and weighted gene co-expression network analysis (WGCNA). The results provide an insight into the theory of peel color formation in evergreen pomegranate fruit.

The biosynthesis of anthocyanins and proanthocyanidins (PAs), components of two main flavonoids in plants, is regulated by environmental factors such as light. We previously found that bagging significantly repressed the biosynthesis of anthocyanins in red ‘Ruby’ mango fruit peel, but induced the accumulation of PAs. However, the molecular mechanism remains unclear. In the current study, transcriptome sequencing was used for screening the essential genes responsible for the opposite accumulation pattern of anthocyanins and PAs by bagging treatment. According to weighted gene co-expression network analysis (WGCNA), structural genes and transcription factors highly positively correlated to anthocyanins and PAs were identified. One flavanone 3-hydroxylase (F3H) and seven structural genes, including one chalcone synthase (CHS), one flavonoid 3’-hydroxylase (F3’H), one anthocyanidin synthesis (ANS), three leucoanthocyanidin reductase (LARs), and one UDP glucose: flavonoid 3-O-glucosyltransferase (UFGT), are crucial for anthocyanin and PA biosynthesis, respectively. In addition to MYB and bHLH, ERF, C2H2, HD-ZIP, and NAC are important transcription factors that participate in the regulation of anthocyanin and PA biosynthesis in ‘Ruby’ mango fruit peel by bagging treatment. Our results are helpful for revealing the transcription regulation mechanism of light-regulated mango anthocyanin and PA biosynthesis, developing new technologies for inducing flavonoid biosynthesis in mangos, and breeding mango cultivars containing high concentrations of flavonoids.

B-box (BBX) transcription factors are critical regulators of light-mediated anthocyanin biosynthesis, influencing peel coloration in plants. To explore their role in red mango cultivars, we identified 32 BBX genes (MiBBX1–MiBBX32) in the mango (Mangifera indica L.) genome using a genome-wide analysis. Phylogenetic and structural analyses classified these genes into five subfamilies based on conserved domains. A collinearity analysis revealed segmental duplication as the primary mechanism of MiBBX gene family expansion, with purifying selection shaping their evolution. A promoter analysis identified numerous light- and hormone-responsive cis-elements, indicating regulatory roles in the light and hormonal signaling pathways. Expression profiling in the ‘Sensation’ cultivar revealed organ-specific patterns, with several MiBBX genes showing higher expression in the peel than in the flesh. Many of these genes also consistently exhibited elevated expression in the peel of red-skinned cultivars (‘Sensation’ and ‘Guifei’) compared to yellow and green cultivars, suggesting their role in red peel pigmentation. Furthermore, postharvest light treatment of ‘Hongmang No. 6’ fruit significantly upregulated multiple MiBBX genes, suggesting their involvement in light-induced anthocyanin accumulation in red mango peel. These findings provide valuable insights into the molecular mechanisms governing light-regulated peel coloration in mango and establish a foundation for functional studies of MiBBX genes in fruit pigmentation.