Abscisic acid promotes novel DNA-binding activity to a desiccation-related promoter of Craterostigma plantagineum.

Abscisic acid-treated callus of the resurrection plant Craterostigma plantagineum tolerates extreme desiccation. Nuclear proteins from tolerant callus bind specific sequence elements in the promoter region of the ABA and desiccation-inducible CDeT27-45 gene. One specific region of the promoter, which is protected from DNAase I treatment by DNA-binding activities, is different from previously reported ABA response elements. Four complexes of nuclear proteins and this DNA region are detected by electrophoretic mobility shift assay: two of these complexes (I and II) are readily detectable in untreated samples and are increased by ABA treatment while two other complexes (III and IV) accumulate only following ABA treatment and are prevented from accumulating by protein synthesis inhibitors. When a fragment containing the novel binding site is deleted from the wild-type promoter the ABA responsiveness of the promoter is removed; however, gain of function experiments using synthetic promoters in a protoplast transient assay suggest that besides the binding site other promoter elements are required. A second region of the promoter, containing the sequence element ACGT which is found in abscisic acid response elements, is also bound by nuclear proteins. The level of this second binding activity is similar in both untreated and ABA- treated cells and promoter/reporter gene constructs which contain only the four ACGT elements of the CDeT27-45 promoter are not ABA responsive in a C. plantagineum transient assay system.