E2F transcription factors play key roles in plant growth and development by regulating the cell cycle. In this study, ClE2F1 was isolated from Chrysanthemum lavandulifolium. This gene encodes a 452-amino-acid protein that contains a DNA-binding domain, marked box domain, pRBR-binding domain, and a nuclear localization signal. Phylogenetic analysis showed that ClE2F1 was most closely related to Arabidopsis thaliana AtE2Fa, AtE2Fb, and AtE2Fc. Transient expression experiments demonstrated that the ClE2F1 protein localizes to the nucleus. Yeast one-hybrid assays showed that ClE2F1 promotes transcriptional activation. The morphology of the OX-6, OX-7, and OX-10 transgenic and wild-type lines was investigated. Plant height, leaf length and width, inflorescence diameter, disc flower diameter, the number of tabulate florets, and ligulate floret length were greater in the OX-6, OX-7, and OX-10 lines than in wild-type plants. Microscopic observation revealed a higher number of cells per unit area but a smaller cell area in the OX-6, OX-7, and OX-10 lines than those in wild-type plants. In addition, the relative expression of cell cycle-associated genes in the OX-6, OX-10, and wild-type plants revealed that the ClPCNA3, ClRNR, ClASF, ClDPa, ClCDKA, and ClCYCD transcript levels were up-regulated in the OX-6 and OX-10 plants, whereas ClRBR and ClKRP5 expression was down-regulated.
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