Integrated transcriptome and metabolome analysis reveals the mechanism for unique dynamic change in the flower color of Lycoris albiflora.

Anthocyanins are pigments that confer color in plants. Although extensive research has been conducted on anthocyanin biosynthesis, the molecularly modulated mechanisms responsible for flower gradient coloration remain largely unknown. Lycoris albiflora 'Astro Girl' flowers gradually turn from white to pink after flowering, making them suitable for studying the regulatory mechanisms of anthocyanin accumulation. To determine the molecular mechanism by which anthocyanin accumulation affects the color patterns in L. albiflora during flowering, we conducted integrated analysis of dynamic coloration in L. albiflora 'Astro Girl' flowers using metabolomics, PacBio full-length transcriptomics, and Illumina RNA sequencing. The main components of anthocyanins were cyanidin derivatives, followed by delphinidin derivatives. By determining the correlation between differentially expressed genes and anthocyanin accumulation, structural genes (LaCHSs, LaF3Hs, LaDFRs, LaANSs, and LaGSTs) and transcription factors (LaMYBs, LabHLHs, LaWD40s, and LaNACs) that contribute to anthocyanin profile dynamics were identified. As a rate-limiting step in anthocyanin production, LaDFR1 gene expression was induced immediately after flowering and then decreased. Functional characterization using virus-induced gene silencing in L. radiata flowers and overexpression in Arabidopsis confirmed that LaDFR1 was responsible for anthocyanin accumulation. Dual-luciferase reporter and yeast one-hybrid assays evaluated the truncated promoter activity and showed that LaNAC4 activated the LaDFR1 promoter. These results also imply that LaNAC4 modulates the LaDFR1 promoter acting as a dual activator and repressor. Taken together, the findings of this research shed light on the molecular mechanism of anthocyanin accumulation in flowers and are useful for the genetic breeding of flower color in Lycoris and other ornamental plants.