Control of chrysanthemum flowering through integration with an aging pathway

Age, as a threshold of floral competence acquisition, prevents precocious flowering when there is insufficient biomass, and ensures flowering independent of environmental conditions; however, the underlying regulatory mechanisms are largely unknown. In this study, silencing the expression of a nuclear factor gene, CmNF-YB8, from the short day plant chrysanthemum ( Chrysanthemum morifolium), results in precocious transition from juvenile to adult, as well as early flowering, regardless of day length conditions. The expression of SQUAMOSA PROMOTER BINDING-LIKE (SPL) family members, SPL3, SPL5, and SPL9, is upregulated in CmNFYB8-RNAi plants, while expression of the microRNA, cmo-MIR156, is downregulated. In addition, CmNF-YB8 is shown to bind to the promoter of the cmo-MIR156 gene. Ectopic expression of cmo-miR156, using a virus-based microRNA expression system, restores the early flowering phenotype caused by CmNF-YB8 silencing. These results show that CmNF-YB8 influences flowering time through directly regulating the expression of cmo-MIR156 in the aging pathway.