STUDIES ON THE TRANSCRIPTION FACTOR VP1 INVOLVED IN ABSCISIC ACID RESPOSIVE GENE EXPRESSION

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G-box-like response elements (ABREs) have been functionally identified in the promoters of various genes. In addition, single copies of ABRE have been found to require a cis-acting, coupling element to achieve ABA induction. A Coupling Element 3 (CE3) sequence, originally identified as such in the barley HVA1 promoter, is found approximately 30-bp downstream of motif A (G-box-like ABRE) in the promoter of Osem gene. The relationship between these two elements was further defined by linker-scan analyzes of a 55-bp fragment of the Osem promoter, which is sufficient for ABA-responsiveness and VP1 activation. The analyzes revealed that both motif A and CE3 sequence were required not only for ABA-responsiveness but also for VP1 activation. Since the sequences of motif A and CE3 were found to be similar, motif-exchange experiments were carried out. The experiments demonstrated that motif A and CE3 were interchangeable by each other with respect to both ABA and VP1 regulation. Furthermore, both sequences were shown to be recognized by a rice bZIP factor OSBZ8. These results indicate that G-box-like ABREs and CE3 are functionally equivalent cis-acting elements.