Abstract: Objective UFO is the first F-box protein discovered in angiosperms, and plays a role in determining floral meristem identity and floral organ growth. In this study, the expression profile and heterologous expression phenotypic traits in A. thaliana were analyzed to explore the gene function of CpUFO and provide a basis for molecular mechanism of floral development in wintersweet (Chimonanthus praecox). Method Based on the constructed transcriptome data of C. Praecox, the CpUFO gene was cloned and the sequence alignment of its encoded protein and phylogenetic analysis were conducted. Quantitative real-time RT-PCR (qRT-PCR) was performed to identify transcript level of CpUFO in different tissues, organs and annual flower buds in different flower development stages. The effects of CpUFO on flowering time and flower organ development of Arabidopsis thaliana were explored by analyzing the phenotypes and relative gene expression of endogenous flowering related gene between the 35S∷CpUFO transgenic Arabidopsis lines and the wild type. Result The obtained cDNA of CpUFO gene was 1 655 bp in full-length, encoding a protein of 403 amino acids residues with highly conserved F-box domain. The expression level of CpUFO was relatively highest in the outer tepal, followed by the inner tepal, and the expression level was lower in fruit, stem, leaf, axillary bud and stamen. Transcript level of CpUFO in annual flower buds showed that relative expression of CpUFO in flower buds of display tepals (DT), initial blooming (IB) and open flower (OF) stages after chilling-induced dormancy breaking was obviously higher than that in the other developmental periods. Compared with Arabidopsis Col-0, 35S::CpUFO transgenic Arabidopsis lines had less rosette leaves and early flowering. Moreover, the endogenous genes of AP1 and FUL in A. thaliana were significantly up-regulated, while TFL1 was significantly down-regulated. Conclusion CpUFO is expressed in different tissues, organs and annual flower buds, and the highest relative expression level is found in the outer tepals and flower buds of open period after dormancy breaking. Meanwhile, overexpression of CpUFO promotes early flowering in Arabidopsis and affects its floral organ development．

Key words: Chimonanthus praecox, UFO gene, F-box family, flower development