Characterization of the MADS-Box Gene CmFL3 in chrysanthemum

Chrysanthemum morifolium is one of the four major cut flowers in the world, with high ornamental and economic value. Flowering time is an important ornamental characteristic of chrysanthemum that affects its value in the market. In Arabidopsis, the FRUITFULL (FUL) gene plays a key role in inducing flowering. Here, we isolated an FUL clade MADS-box gene, CmFL3, from chrysanthemum inflorescence buds. CmFL3 localized in the cellular membrane and nucleus, and showed no transcriptional activity in yeast. The qRT-PCR assay showed that CmFL3 was strongly expressed in the leaves, receptacles, and disc floret petals. Furthermore, CmFL3 was mainly detected in the inflorescence meristem and bract primordia using in situ hybridization. Similar to Arabidopsis, overexpression of CmFL3 in chrysanthemum induced early flowering. Particularly, the expression level of CmAFT was downregulated, whereas that of CmFTL3 was upregulated in the leaves of transgenic chrysanthemum lines. Meanwhile, the overexpression of CmFL3 in Arabidopsis also led to earlier flowering. Furthermore, the expression of AtFT, AtAP1, AtLFY, and AtFUL was significantly increased in CmFL3 transgenic Arabidopsis. The present study verified the function of CmFL3 in regulating flowering time and further revealed that it could affect the expression of other flowering-related genes-CmAFT and CmFTL3. Therefore, the CmFL3 gene may be an important candidate for genetic breeding aimed at regulating flowering.