The CmCYC2 Factors Regulated the Different Biosynthesis and Distribution of Phenolic Compounds in the Capitulum of Chrysanthemum Morifolium ‘Hangju’

Chrysanthemum morifolium Ramat. is an important industrial crop with a high medicinal value, whose capitulum consists of ray and disc florets containing numerous bioactive components, such as flavonoids and phenolic acids. However, the distribution and accumulations of the bioactive metabolites in florets of Chrysanthemum morifolium were unclear. Herein, the ray and disc florets of Chrysanthemum morifolium were separated for comparing the bioactive metabolites. The contents of phenolic compounds and antioxidant activities were significantly different between the two florets. The metabolomic analysis identified 203 and 241 differential metabolites between ray and disc florets at two flowering stages. The derivatives of quercetin, isorhamnetin, tricin, and caffeoylquinic acid were enriched in the disc florets, while apigenin, kaempferol, acacetin, and their glycosides mainly accumulated in the ray florets. Besides, the results of transcriptome and qRT-PCR suggested that the F3H, F3′H, and FLS genes highly expressed in disc florets, while the FNS gene was well expressed in ray florets, which explained the different distribution of phenolic compounds between ray and disc florets. Furthermore, the expression of CmCYC2 genes was found to be significantly related to the distribution of flavones by correlation analysis. It was proved by the luciferase reporter assay that CmCYC2a and CmCYC2d factors could bind and activate the CmFNS promoter to regulate the flavones biosynthesis in ray florets. These results revealed the significant difference of metabolite contents and gene expression profiles between ray and disc floret in Chrysanthemum morifolium and demonstrated that the quality of Chrysanthemum morifolium ‘Hangju’ was closely relevant to its flower morphology.