An abiotic stress-responsive bZIP transcription factor from wild and cultivated tomatoes regulates stress-related genes

Wild relatives of cultivated tomato (Solanum lycopersicum) are resistant to a wide range of abiotic and biotic stress conditions. In an effort to understand the molecular mechanisms of salt stress resistance in the wild and cultivated Solanum species, a basic leucine zipper (bZIP) transcription factor was identified in S. chilense, S. peruvianum and S. lycopersicum and named ScAREB1, SpAREB1 and SlAREB1, respectively. Deduced amino acid sequences of the three proteins are 97% identical among them and present high homology with the ABF/AREB subfamily of transcription factors described in different plant species, including Arabidopsis (ABF2, 54% identical) and tobacco (PHI-2, 50% identical). Expression of these orthologous genes is upregulated similarly in the three species by salt stress. The expression of SlAREB1 was further investigated in S. lycopersicum and found to be induced by drought, cold and abscisic acid. To investigate the possible role of this transcription factor in response to abiotic stress, a simple transient expression assay was used for rapid analysis of genes regulated by SlAREB1 in tomato and tobacco by means of Agrobacterium-mediated transformation. Tobacco leaves expressing SlAREB1 showed upregulation of stress-responsive genes such as RD29B, the LEA genes ERD10B and TAS14, the transcription factor PHI-2 and a trehalose-6-phosphate phosphatase gene. These results suggest that this class of bZIP plays a role in abiotic stress response in the Solanum genus.