Abstract: 【Objective】The cDNA sequence of chrysanthemum rhythms clock output gene GIGANTEA was cloned, and the bioinformatics of the sequence and the relative quantitative expression of mRNA were analyzed.【Method】 Polymerase chain reaction (PCR) combined with 5′RACE, and 3′RACE technology were used to clone the full length cDNA of chrysanthemum rhythms clock output gene CmGI，analysis of sequence of nucleotides and code of protein was made by using the software of bioinformatics. Protein structure prediction of 3D modeling was made by using the online modeling software. The relative quantitative expression analysis of CmGI was conducted by real-time quantitative fluorescence PCR technology and 2-△△Ct method. 【Result】The cDNA sequence of GIGANTEA was cloned from chrysanthemum ‘Jniba’, the full-length cDNA was 3 461 bp, open reading frame (ORF ) was 3 453 bp, and encoded 1 150 amino acids. Sequence analysis showed that the genetic code of protein was homologous with plant rhythms clock output gene GIGANTEA, named CmGI gene. The sequence was submitted to GenBank, and the registration number is JQ043439. Sequence alignment displayed that it was a similarity of 76% and 75% with GIGANTEA of Vitis vinifera，Ricinus communis, respectively. The phylogenetic tree showed that chrysanthemum CmGI and Arabidopsis thaliana GIGANTEA are closest in molecular evolution distance, followed by Brassica rapa GIGANTEA. It was speculated that CmGI protein has six transmembrane spiral across a cell membrane many times. They are transcription factors, located in the nucleus and it is a non-secretory protein. They do not have a signal peptide. CmGI 3D structure modeling projections show that the protein core structure accords with the transcription factors and the function of the common DNA combining domain HTH and HLH. Fluorescent relative quantitative analysis shows that the expression patterns of chrysanthemum CmGI are circadian rhythms expression. At different flower bud differentiation stage, the CmGI gene in the leaf blade mRNA level is different, two peak values were appeared in the flower bud differentiation start-up and floret primordia middle differentiation periods. The tissue culture plantlets leaves and buds under long-day conditions, during alabastrum period are all trace expression and was in the order of leaves＞tongue shape flower＞tubular flowers during flowers blooming period. 【Conclusion】Rhythms clock output gene CmGI was cloned from chrysanthemum, further research on this gene will help exploration of photoperiod pathway of the flower of chrysanthemum molecular control mechanism and could be used as the target gene of molecular breeding of flowering phase.

Key words: Chrysanthemum morifolium, flower bud differentiation, rhythm clock output gene CmGI, quantitative expression