Characterization of five novel dehydration-responsive homeodomain leucine zipper genes from the resurrection plant Craterostigma plantagineum.

Homeodomain leucine zipper (HDZip) genes encode putative transcription factors that are unique to plants. A function in regulating processes that are specific for plants is postulated, such as responses to environmental cues and developmental signals. This is supported by a growing body of evidence resulting from studies of HDZip genes in a variety of species. In addition to the previously isolated CPHB-1 and -2 genes, this paper reports the isolation of members of five families of Craterostigma plantagineum homeobox leucine zipper genes (CPHB) via a yeast one-hybrid screening approach. Based on the sequence homology and protein interactions the encoded proteins (CPHB-3/4/5/6/7) were classified into HDZip class II and I genes. Homo- and heterodimerization of CPHB proteins within the same structurally related class has been demonstrated and the DNA-binding activity of CPHB proteins to two homeodomain recognition elements (HDE1 and HDE2) has been compared in yeast. All families of CPHB genes were modulated in their expression in response to dehydration in leaves and roots. CPHB-6 and CPHB-7 transcripts accumulated in leaves during early stages of dehydration and decreased after prolonged dehydration. Both transcripts were also induced in ABA-treated callus. CPHB-3/4/5 were down-regulated by dehydration in both leaves and roots. The results support the role of HDZips in regulating programs of gene expression in C. plantagineum that lead to desiccation tolerance.