Isolation and functional analysis of the ClM8-FRUITFULL-like MADS-box gene from Chrysanthemum lavandulifolium

• Chrysanthemum lavandulifolium is one of the original species of chrysanthemum.
• We isolated the ClM8 gene in full length from C. lavandulifolium, it was an ortholog of FUL.
• ClM8 is a single copy in C. lavandulifolium and localised to the nucleus.
• We conducted the expression profiling of ClM8 in C. lavandulifolium, it was strongly expressed in flowers.
• Overexpressing ClM8 promoted flowering and produced terminal flower in transgenic Arabidopsis plants, the development of fruits and leaves were also affected.

AP1/FUL-like genes encode class-specific MADS box transcription factors in angiosperms and play important roles in the plant floral transition and floral organ identity. Chrysanthemum lavandulifolium (Fisch. ex Trautv.) Makino is one of the original species of Chrysanthemum. Understanding the function of AP1/FUL-like genes in C. lavandulifolium provide molecular-level insight into the flowering mechanism of Chrysanthemum. Here, an AP1/FUL-like gene was isolated from C. lavandulifolium. Sequence and phylogenetic analyses indicated that this gene, ClM8, belongs to the euFUL clade of the AP1/FUL-like genes. We observed different expression levels of ClM8 in C. lavandulifolium roots, stems, fruits and leaves and high expression in the flowers. A subcellular localisation assay showed that ClM8 is localised to the nucleus in vivo. The over-expression of ClM8 in Arabidopsis resulted in altered flowering time and inflorescence structure. These aberrant, transgenic Arabidopsis plants showed early flowering following the production of four to six small rosette leaves, lateral flowers and a composite terminal flower. The terminal flower consisted of two or four pistils surrounded by an abnormal number of sepals, petals and stamens. In addition, the morphology of the style of 35S::ClM8 plants silique differed from wild type, appearing thinner and longer. Further investigation suggested that the expression levels of FLOWERING LOCUS T (FT), LEAFY (LFY) and APETALA1 (AP1) were apparently increased in ClM8-transgenic Arabidopsis. Thus, we speculate that ClM8 promoted flowering in Arabidopsis due to the upregulation of FT. Taken together, our results suggest that ClM8 is involved in flowering induction and floral development that might also play a role in the development of fruits and leaves.