Abstract:MADS-box family protein is an important class of transcription factors regulating flowering. FLC is a member of MADS-box transcription factors, and the FLC gene is controlled by many pathways, and then to regulate the flowering. We cloned a FLC-homolog gene in male flower buds from Populus simonii×Populus nigra. The open reading frame (ORF) of this gene had 726 bp which encoded a protein containing 241 amino acid. The molecular weight of the predicted protein was 27.559 KD, and the pI was 9.37. By real-time quantitative PCR, vernalization could down-regulate the expression of PnFLC 57.9%-84% in the root, stem and leaves tissues of poplar. By GUS staining, the promoter of the PnFLC is highly expressed in actively dividing tissues. Furthermore, by transforming Arabopsis, PnFLC down-regulated the expression of AtAP1, AtSOC1 and AtFT, while delayed the flowering in Arabidopsis.