Integrated metabolome and transcriptome reveals the mechanism of the flower coloration in cashew Anacardium occidentale

•Flavonoids metabolism influenced the formation of flower color in cashew.•Metabolomics and RNA-seq identified candidate metabolites and genes in flavonoids biosynthesis.•WGCNA identified potential transcription factors that regulated the expression of candidate genes. Cashew is a widely attractive food in the world with high nutritional value for human health. Flower color is an important trait that plays a key role in reproductive ecology and species evolution in cashew plants. In this study, we chose two cashew cultivars for research objects characterized as different flower coloration. B2_5 exhibited steady white color during flowering, while B7 exhibited a color transition from white to red in its blooming period. However, the molecular mechanisms underlying flower coloration in both cashew cultivars remains unclear. By comparative metabolome analysis, we identified 8 flavonoid compounds were markedly accumulated in B7 during flowering, especially delphinidin-3-O-glucoside and peonidin-3-glucoside. These hub metabolites explained the variety difference in flower coloration between B7 and B2_5 cashew cultivars. Further transcriptome analysis identified 9 key structural genes in flavonoid biosynthesis that were significantly up-regulated, especially CHI, FLS and LAR, which explained the variety difference in flower coloration between both cashew cultivars. The construction of co-expression network showed RAP2-2, NAC22, MYB78, MYB62 and MYB1 probably modulated the expression of three candidate structural genes. This study sheds light on the molecular mechanism of flower coloration in B7 cultivar and reveals the variety difference in flower coloration between two cultivars, these results expect to provide a worthy guidance for flower coloration in cashew.