Current understanding of regulation of GBF3 under abiotic and biotic stresses and its potential role in combined stress tolerance

Abstract

G-box binding factors (GBFs) belong to basic leucine zipper (bZIP) super family of transcription factors. Among six reported members of Arabidopsis thaliana GBFs, AtGBF3 transcripts has been shown to accumulate to high levels in dry seed, stamens, mature pollen and siliques. Amino acid sequence analysis of AtGBF3 reveals presence of proline rich region at 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 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 expression of stress related genes. Till now target genes of GBF3 and mechanism of their regulation during individual and combined abiotic - biotic stresses is not 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.