Identification of a dehydration and ABA-responsive promoter regulon and isolation of corresponding DNA binding proteins for the group 4 LEA gene CpC2 from C. plantagineum.

The resurrection plant Craterostigma plantagineum (Scrophulariaceae) is used as a model system to investigate the molecular and biochemical basis of desiccation tolerance. Genes which contribute to desiccation tolerance are expressed during dehydration of this plant. One of the dehydration-induced genes is CpC2, a group 4 LEA gene. The CpC2 promoter was analysed and a core promoter region (CPR) was identified which is critical for the responsiveness of the gene to dehydration and the plant hormone ABA. The CPR motif contains two ABA-response elements (ABRE) and a binding site for HDZIP transcription factors. A yeast one-hybrid screen was performed to isolate CPR binding proteins. This resulted in the isolation of a bZIP transcription factor (CpbZIP1) and three highly conserved CpHistone H3 proteins. Two of these CpHistone H3 proteins are constitutively expressed histone H3 variants which are suggested to be involved in gene regulation via histone modification. The CpbZIP1 belongs to the group S of bZIP genes which possess long 5'-UTRs with a putative regulatory function. A second very similar bZIP clone, CpbZIP2, was isolated which contains a conserved small upstream open reading frame (uORF) within the 5'-leader sequence. A possible regulatory role of the uORF is discussed.