The rab16B promoter of rice contains two distinct abscisic acid-responsive elements

To localize abscisic acid (ABA)-inducible gene expression of rab16 genes, rab16A promoter was linked to the gusA reporter gene encoding beta-glucuronidase and introduced into rice (Oryza sativa L.) plants. The activity of rab16A promoter was induced by ABA and osmotic stresses in various tissues of vegetative and floral organs. In anthers and embryos, rab16A promoter was active in the absence of ABA. To elucidate cis-elements of the rab16 promoter that confer ABA-inducible expression, variously modified 40-bp fragments (-264 to -225) of the rab16B promoter were fused to a truncated (-46 bp) cauliflower mosaic virus 35S minimal promoter, and their activities in protoplasts were analyzed. The transient assays revealed that the 40-bp fragment consists of two separate ABA-responsive elements, motif 1 (AGTACGTGGC) and motif III (GCCGCGTGGC). Motif I and motif III are both required for ABA induction; however, each can substitute for the other. Further analyses of these motifs indicated that motif III has a distinct DNA sequence specificity as an ABA-responsive element from motif I, suggesting that the two motifs interact with different transcription factors in vivo.