bZIP and DOF transcription factors in the regulation of gene expression in barley endosperm

The protein quality of cereal grain is determined by the quantity and composition of the prolamin storage proteins (hordeins in barley) that are specifically synthesized in the endosperm and that are regulated at the transcriptional level. Most prolamin gene promoters contain a bipartite sequence motif in the -300 region that becomes occupied early in endosperm development by nuclear trans -acting factors. cDNAs have been characterized from barley endosperm encoding DNA-binding proteins with affinity towards the two halves of the -300 motif: 5'TGTAAAG-3' prolamin box; PB) and 5'-GTGAGTCAT-3'(GCN4-like; GLM), respectively. The barley PB binding factor is a zinc finger of the DOF class while the GLM binding factors belong to the bZIP class of transcription factors. Experiments in vivo and in vitro are described that strongly implicate these factors as important activators of hordein gene expression and suggest their evolutionary conservation among small grain cereals.