The loss of a single residue from CmFTL3 leads to the failure of florigen to flower

The product of CmFTL, a gene represented by multiple transcripts, is an important determinant of floral development in chrysanthemum. Here, a new transcript CmFTL3ps4 which contains three different amino acid residues compared to CmFTL3 was characterized. When driven by the Arabidopsis thaliana FT promoter, CmFTL3ps4 expression did not rescue the late flowering phenotype of the A. thaliana ft-10 mutant. When the variant sequences CmFTL3Q130K, CmFTL3G136A and CmFTL3D145N were heterologously expressed in A. thaliana, both CmFTL3G136A and CmFTL3D145N were shown to accelerate flowering, although to a different extent. There was no significant difference in the number of leaves which had formed before the flowering of either the CmFTL3Q130K or the CmFTL3ps4 transgenic lines. Neither the transgenic expression of CmFTL3ps4 or CmFTL3Q130K was able to rescue the ft-10 mutant phenotype. A bimolecular fluorescence complementation assay confirmed that CmFTL3Q130K did not interact with CmFDL1, a homolog of the bZIP transcription factor FD. The conclusion was that a novel residue change affected FT activity through its disruption of the interaction with CmFDL1.