Identification and characterization of two chrysanthemum (Dendronthema X moriforlium) DREB genes, belonging to the AP2/EREBP family

Two DREB-like genes, designated as DmDREBa and DmDREBb, were isolated from chrysanthemum by RACE approach. The DmDREBa and DmDREBb genes encoded proteins of 191 and 185 amino acid residues with the predicted molecular mass of 21.66 and 20.99 kDa, respectively. Both DmDREBs proteins comprised a typical EREBP/AP2 domain, a DREB1-type nuclear localization signal (NLS) before the EREBP/AP2 domain and a DSAWR sequence after the domain. Phylogenetic analysis suggested that both DmDREBs were attributable to the DREB1 subgroup. Quantitative real-time PCR analysis revealed that both genes were accumulated more in leaves and stems than in roots and flowers. Moreover, DmDREBb reacted earlier and accumulated with higher levels than DmDREBa under cold treatment. Expression of DmDREBa and DmDREBb declined dramatically within 0.5 h of exposure to 100 mu M ABA. Besides, DmDREBb expression was variable and recovered to pre-ABA levels at 2, 6 and 12 h, while DmDREBa expression remained low during the 24 h exposure period. Furthermore, both genes expression was totally inhibited at 40 degrees C. In addition, these two DmDREB proteins were also found to have transcriptional activity and had the DRE-binding capacity as shown by yeast one-hybrid system and were localized to the nuclei of cells. To our knowledge, this is the first report on isolation of DREB-like genes in chrysanthemum. This study showed that DmDREBs may play a regulatory role in abiotic stress responses and provided evidence of differences in the timing and level of expression between two homologous genes in plants under abiotic stress conditions.