Overlap of Viviparous1 (VP1) and abscisic acid response elements in the Em promoter: G-box elements are sufficient but not necessary for VP1 transactivation.

The relationship between promoter sequences that mediate Viviparous1 (VP1) transactivation and regulation by abscisic acid (ABA) in the wheat Em promoter was investigated using deletion analysis and directed mutagenesis. The Em1a G-box is strongly coupled to VP1 transactivation as well as to ABA regulation; however, the Em promoter includes additional components that can support VP1 transactivation without ABA responsiveness or synergism. Oligonucleotide tetramers of several G-box sequences, including Em1a, Em1b, and the dyad G-box element from the UV light-regulated parsley chalcone synthase gene, were sufficient to confer VP1 transactivation and the synergistic interaction with ABA to the -45 cauliflower mosaic virus 35S core promoter. These data suggest that VP1 can activate transcription through at least two classes of cis-acting sequences, including the G-box elements and the Sph regulatory motif found in the C1 promoter. The contrasting roles of these motifs in the Em and C1 promoters suggest a basis for the differential regulation of the corresponding genes by VP1.