A root-specific bZIP transcription factor is responsive to water deficit stress in tepary bean (Phaseolus acutifolius) and common bean (P-vulgaris)

Root cDNA libraries were differentially screened to isolate water deficit-responsive transcripts in the relatively drought-resistant plant tepary bean (Phaseolus acutifolius). A novel root-specific, water deficit-responsive transcript was identified and predicted to encode a bZIP transcription factor. The orthologous form of this gene was isolated from the drought-sensitive P. vulgaris and the patterns of expression of these genes compared. These genes have predicted amino acid sequences in the bZIP domain that are 64% similar to a soybean bZIP protein. There were three amino acid differences between the P. acutifolius bZIP and the P. vulgaris gene product. Both species transcribed this gene in a root-specific and water deficit-responsive manner. The cell-specific pattern of expression for the gene was determined using in situ hybridization and immunolocalization. Two tissues in the root accumulated the protein: epidermis and phloem. The nuclear localization of this protein was determined by electron microscopy. The bZIP protein accumulated in the nuclei of both the epidermal cell and the vascular cell in response to water deficit stress in both species in a similar manner.