ABFs, a family of ABA-responsive element binding factors

Abscisic acid (ABA) plays an important role in environmental stress respons es of higher plants during vegetative growth. One of the ABA-mediated respo nses is the induced expression of a large number of genes, which is mediate d by cis-regulatory elements known as abscisic acid-responsive elements (AB REs). Although a number of ABBE binding transcription factors have been kno wn, they are not specifically from vegetative tissues under induced conditi ons. Considering the tissue specificity of ABA signaling pathways, factors mediating ABA-dependent stress responses during vegetative growth phase may thus have been unidentified so far. Here, we report a family of ABBE bindi ng factors isolated from young Arabidopsis plants under stress conditions. The factors, isolated by a yeast one-hybrid system using a prototypical ABB E and named as ABFs (ABRE binding factors) belong to a distinct subfamily o f bZIP proteins. Binding site selection assay performed with one ABF showed that its preferred binding site is the strong ABBE, CACGTGGC. ABFs can tra nsactivate an ABBE-containing reporter gene in yeast. Expression of ABFs is induced by ABA and various stress treatments, whereas their induction patt erns are different from one another, Thus, a new family of ABBE binding fac tors indeed exists that have the potential to activate a large number of AB A/stress-responsive genes in Arabidopsis.