CONSERVATION IN WHEAT HIGH-MOLECULAR-WEIGHT GLUTENIN GENE PROMOTER SEQUENCES - COMPARISONS AMONG LOCI AND AMONG ALLELES OF THE GLU-B1-1 LOCUS

The high-molecular-weight glutenin (HMW) genes and encoded subunits ar e known to be critical for wheat quality characteristics and are among the best-studied cereal research subjects. Two lines of experiments w ere undertaken to further understand the structure and high expression levels of the HMW-glutenin gene promoters. Cross hybridizations of cl ones of the paralogous x-type and y-type HMW-glutenin genes to a compl ete set of six genes from a single cultivar showed that each type hybr idizes best within that type. The extent of hybridization was relative ly restricted to the coding and immediate flanking DNA sequences. Addi tional DNA sequences were determined for four published members of the HMW-glutenin gene family (encoding subunits Ax2 double dagger, Bx7, D x5, and Dy10) and showed that the flanking DNA of the examined genes d iverge at approximately -1200 bp 5' to the start codon and 200-400 bp 3' to the stop codon. These divergence sites may indicate the boundari es of sequences important in gene expression. In addition, promoter se quences were determined for alleles of the Bx gene (Glu-B1-1), a gene reported to show higher levels of expression than other HMW-glutenin g enes and with variation among cultivars. The sequences of Bx promoters from three cultivars and one wild tetraploid wheat indicated that all Bx alleles had few differences and contained a duplicated portion of the promoter sequence ''cereal-box'' previously suspected as a factor in higher levels of expression. Thus, the ''cereal-box'' duplication p receeded the origin of hexaploid wheat, and provides no evidence to ex plain the variations in Bx subunit synthesis levels. One active Bx all ele contained a 185-bp insertion that evidently resulted from a transp osition event.