BARLEY BLZ1 - A BZIP TRANSCRIPTIONAL ACTIVATOR THAT INTERACTS WITH ENDOSPERM-SPECIFIC GENE PROMOTERS

A cDNA encoding a bZIP transcription factor was obtained from barley e ndosperm and used to identify the corresponding gene from a genomic li brary. The gene, designated Blz1, contained six exons and five introns , plus a 442 nt-long 5'-untranslated leader sequence, and was located on chromosome 5H. The Blz1 mRNA was detected early in endosperm develo pment and was also expressed in roots and leaves. The BLZ1 protein was a potent transcriptional activator in a yeast system; 85% of its acti vity was associated with the first 203 amino acid residues at the N-te rminus, which included two acidic regions. Presumptive involvement of Blz1 in the regulation of gene expression in endosperm was ascertained by the DNA-binding properties of BLZ1 in electrophoretic mobility shi ft assays (EMSA) and by transient expression in barley developing endo sperms, using, as effecters, Blz1 in both sense and antisense orientat ions. In the co-bombardment experiments, the P-glucuronidase (GUS) rep orter gene responded to Blz1 if under the control of the endosperm-spe cific Itr1 promoter or under a synthetic promoter containing the endos perm box of gene Hod. Sucrose synthase promoters Ss1 and Ss2 and synth etic promoters containing mutated sequences of Hor2 were unaffected in trans by Blz1.