Arabidopsis bZIP1 Transcription Factor Binding to ABRE cis-Element Regulates Abscisic Acid Signal Transduction

Abscisic acid (ABA) is a phytohormone and mediates response and adaptation of higher plants to various environmental stresses during vegetative growth. The basic leucine zipper (bZIP) transcription factors are also important regulators of plant development and abiotic resistance, acting through either ABA-dependent or ABA-independent mechanisms. In this study, the involvement of the AtbZIP1 gene in plant responsiveness to ABA was investigated and characterized. As confirmed by PCR and reverse transcription PCR (RT-PCR), AtbZIP1 has been silenced in mutant Arabidopsis ko-1 (SALK_059343) and ko-2 (SALK_069489C). The AtbZIP1 knockout plants reduced the sensitivity to ABA both at the seed germination stage and the seedling stage, with improvement in rates of germination, leaf opening/greening, and primary root length. For investigating whether the regulation of AtbZIP1-mediated ABA responsiveness depended on the ABA-responsive elements (ABRE), the AtbZIP1 HIS6 fusion protein was expressed in Escherichia coli. The AtbZIP1 HIS6 was specifically bound to the ABRE cis-elements. According to the results of semiquantitative RT-PCR analysis, AtbZIP1 disruption altered expressions of some ABA responsive genes, such as NCED3, RD22, KIN1, and RD29A. The results indicated that AtbZIP1 regulates ABA signal transduction by binding to the ABREs and altered the expressions of the ABA responsive genes.