PsHY5 functions as a positive transcription factor of light-induced anthocyanin accumulation in Paeonia suffruticosa cut flowers

As secondary metabolites, anthocyanins largely contribute to flower pigmentation. Light serves as a key stimulus for anthocyanin production in plants, in which HY5 functions as the crucial transcription factor in photomorphogenesis and positively regulates light-induced anthocyanin biosynthesis. However, the anthocyanin accumulation pattern regulated by light in tree peony (Paeonia suffruticosa Andr.) cut flowers and the function of PsHY5 in this process remain unknown. Current research has investigated the pigmentation of cut flowers of the tree peony variety ‘Taiyang’ in response to various light intensities. Compared with the results of the weak light-treated group, in which cut flowers were placed under indoor illumination (∼50 μmol m⁻² s⁻¹), the 300 μmol m⁻² s⁻¹ light intensity increased the color of the cut flowers, increased the anthocyanin contents in the petals, and increased the expression of most genes in the anthocyanin pathway; however, the petal color quality under the completely dark treatment was poorer because of the much lower anthocyanin contents. Moreover, PsHY5, the crucial transcription factor involved in the light signaling pathway, was isolated from the petals of tree peony. Its expression level was upregulated under intense light treatment but downregulated under dark treatment compared to that under weak light. The PsHY5 protein can activate the transcription of PsCHS1 by directly binding to its promoter, thus regulating anthocyanin metabolism under different light intensities. Furthermore, PsHY5-overexpressing Arabidopsis thaliana seedlings apparently accumulated more anthocyanins under both normal and high light intensities. Our findings confirmed that high light intensity contributes to anthocyanin accumulation in tree peony cut flowers and that PsHY5 is a positive transcription factor in this process.