In vivo footprinting of a low molecular weight glutenin gene (LMWG-1D1) in wheat endosperm.

The quality of the wheat grain is determined by the quantity and composition of storage proteins (prolamins) which are synthesized exclusively in endosperm tissue. We are investigating the mechanisms underlying the regulation of expression of a prolamin gene, the low molecular weight glutenin gene LMWG-1D1. The LMWG-1D1 promoter contains the endosperm box, a sequence motif highly conserved in the promoter region of a large number of storage protein genes, which is thought to confer endosperm-specific expression of prolamin genes. Here we show by in vivo DMS footprinting of wheat endosperm tissue that the endosperm box becomes occupied by putative trans-acting factors during grain ripening. During early stages of development the endosperm motif within the 5' half of the endosperm box becomes occupied first, followed by binding of a second activity to a GCN4/jun-like motif in the 3' half just prior to the stage of maximum gene expression. Occupancy of the endosperm box is highly tissue-specific: no protection was observed in husk and leaf tissues. Several binding activities were identified in vitro from nuclear protein extracts of wheat endosperm which bind specifically to the endosperm and GCN4/jun motifs identified by in vivo footprinting.