ABSTRACT
G-box binding factors (GBFs) belong to the basic leucine zipper (bZIP) super family of transcription factors. Among six reported members of Arabidopsis thaliana GBFs, AtGBF3 transcripts have been shown to accumulate to high levels in dry seed, stamens, mature pollen and siliques. Amino acid sequence analysis of AtGBF3 reveals the presence of a proline rich region at the N-terminus and basic leucine zipper domain at C-terminus. Earlier, it has been demonstrated that GBFs bind to the G-box element found within the promoter of stress responsive genes, including alcohol dehydrogenase (AtAdh), and activate its transcription. Expression profile of AtGBF3 depicts an increase in mRNA levels in plants under drought, osmotic, heat, salt and cold stress and biotic stresses. In silico analysis reveals GBF3 localization in nucleus and cytoplasm. Cues from localization studies on GBF3 homologs suggest that upon stress signal perception, GBF3 is phosphorylated and localized to nucleus where it can regulate the expression of stress related genes. Until now, target genes of GBF3 and the mechanism of their regulation during individual and combined abiotic and biotic stresses have not been comprehensively reviewed. Through our analysis in this review, we propose GBF3 as major player in integrating abscisic acid and salicylic acid cross talk during combined stress.
