Not Necessary for VP1 Transactivation

The relationship between promoter sequencs that mediate Viviparousl (VP1) transactivation and regulation by abscisic acid (ABA) in the wheat Em promoter was investigated using deletion analysis and directed mutagenesis. The Emla 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 severa1 G-box sequences, including Emla, Emlb, and the dyad G-box element from the UV light-regulated parsley chalcone synthase gene, were sufficient to confer VPI 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 C7 promoter. The contrasting roles of these motifs in the Em and C7 promoters suggest a basis for the differential regulation of the corresponding genes by VP1.