Abstract：F-box protein, as one component of SCF ubiquitin-ligase (skp1-cullin1-F-box) complex, is involved in growth, cell division and hormone responses of plants. To better understand the molecular mechanisms of plantlet formation of Kalanchoe daigremontiana, an F-box protein, KdFBX(GenBank No. KU740356), was cloned using rapid amplification of cDNA ends (RACE) PCR. KdFBX gene consists of an ORF of 987 bp which was predicted to encode a 382 amino acid residues long protein of 37.72 kD with an isoelectric point of 4.4. KdFBX showed homology to orthologs from Ricinus communis, Gossypium raimondii and other plants. Phylogenetic analysis showed that KdFBX protein was most related to Arabidopsis thaliana. No obvious transmembrane region, signal peptide or cleavage were observed. KdFBX protein was a water-soluble and non-secreted protein that located in the cytoplasm. 247 amino acids of KdFBX protein were completely matched to the B chain of the ubiquitin ligase substrate complex, and the backbone structure, as well as the side chain structure was reasonable through Ramachandran analysis. Real-time PCR analysis revealed that KdFBX transcript was expressed highly in root (2.5 times compared to petiole) and down-regulated under osmotic stress. This study characterized the novel KdFBX gene from K. daigremontiana for the first time, and the results may be useful for further functional determination of this gene.
