Barley BLZ1: a bZIP transcriptional activator that interacts with endosperm-specific gene promoters

Resumen

A cDNA encoding a bZIP transcription factor was obtainedfrom barley endosperm and used to identify the corres-ponding gene from a genomic library. The gene, designatedBlz1, contained six exons and five introns, plus a 442 nt-long 59-untranslated leader sequence, and was located onchromosome 5H. TheBlz1mRNA was detected early inendosperm development and was also expressed in rootsand leaves. The BLZ1 protein was a potent transcriptionalactivator in a yeast system; 85% of its activity was associ-ated with the first 203 amino acid residues at the N-terminus, which included two acidic regions. Presumptiveinvolvement ofBlz1in the regulation of gene expressionin endosperm was ascertained by the DNA-binding proper-ties of BLZ1 in electrophoretic mobility shift assays (EMSA)and by transient expression in barley developing endo-sperms, using, as effectors,Blz1in both sense and anti-sense orientations. In the co-bombardment experiments,theβ-glucuronidase (GUS) reporter gene responded toBlz1if under the control of the endosperm-specificItr1promoter or under a synthetic promoter containing theendosperm box of geneHor2. Sucrose synthase promotersSs1andSs2and synthetic promoters containing mutatedsequences ofHor2were unaffected in trans byBlz1.