THE MAIZE TRANSCRIPTION FACTOR OPAQUE-2 ACTIVATES A WHEAT GLUTENIN PROMOTER IN PLANT AND YEAST-CELLS

The promoter of the wheat low-molecular-weight glutenin (LMTYG1D1) gen e contains a cis element called the GCN4 like motif (GLM) which has lo w homology to one class of binding site for the maize endosperm-specif ic b-ZIP transcription factor Opaque-2 (O2). Previous work has shown t hat the GLM element interacts with the nuclear factor ESBFII during wh eat endosperm development at the time of maximum transcription of the LMWG1D1 gene. In this paper we demonstrate that O2 binds to the GLM el ement and can activate high levels of transcription from the wheat GLM in transient assays in plant protoplasts and in yeast cells. Lower le vels of O2 activation through the GLM element in yeast containing a de fective GCN4 gene showed that GCN4 was necessary for high levels of O2 transcriptional activation, indicating that O2 may need to heterodime rise with GCN4 to activate transcription in yeast. These observations provide evidence that the GLM represents a new type of O2 DNA-binding site, and support a postulate that an O2 homologue may activate endosp erm-specific expression of wheat storage protein genes.