OsDREB4 Genes in Rice Encode AP2-Containing Proteins that Bind Specifically to the Dehydration-Responsive Element

Most dehydration-responsive element-binding (DREB) factors interact specifically with the dehydration-responsive element (DRE) and control the expression of many stress-inducible genes in Arabidopsis. In rice (Oryza sativa L. cv. Lansheng), we cloned three DREB homologs: OsDREB1-1, OsDREB4- 1, and OsDREB4-2. The deduced amino acid sequences revealed that each protein contained a potential nuclear localization signal, an AP2 DNA-binding domain, and a possible acidic activation domain. The yeast one-hybrid assay indicated that both OsDREB4-1 and OsDREB4-2 proteins specifically bound to DRE and activated expression of the dual reporter genes of histidine (HIS3) and galactosidase (LacZ). In rice seedlings,expression of OsDREB4-1 was induced by dehydration and high salt, whereas OsDREB1-1 and OsDREB4-2 were expressed constitutively. Under normal growth conditions, OsDREB1-1 was expressed strongly in the leaf, sheath, and spike, was expressed relatively weak in the stem and only faintly expressed in the roots,whereas expression of transcripts of OsDREB4-1 and OsDREB4-2 was higher in the roots, stem, and spike,lower in the leaf, and undetectable in the sheath. Together, these results imply that expression of the OsDREB genes could be controlled by specific aspects of differentiation or development. Thus, OsDREB4-1 could function as a trans-acting factor in the DRE/DREB regulated stress-responsive pathway.