ARABIDOPSIS-THALIANA ETHYLENE-RESPONSIVE ELEMENT-BINDING PROTEIN (ATEBP), AN ETHYLENE-INDUCIBLE, GCC BOX DNA-BINDING PROTEIN INTERACTS WITHAN OCS ELEMENT-BINDING PROTEIN

Ocs elements are a group of promoter sequences required for the expres sion of both pathogen genes in infected plants and plant defense genes , Genes for ocs element binding factors (OBFs), belonging to a specifi c class of basic-region leucine zipper (bZIP) transcription factors, h ave been isolated in a number of plants, Using protein-protein interac tion screening with OBF4 we have isolated AtEBP, an Arabidopsis protei n that contains a novel DNA-binding domain, the AP2/EREBP domain, One class of proteins that contain this domain are the tobacco ethylene-re sponsive element binding proteins (EREBPs). The EREBPs bind the GCC bo x that confers ethylene responsiveness to a number of pathogenesis rel ated (PR) gene promoters, AtEBP expression is inducible by exogenous e thylene in wild-type plants and AtEBP transcripts are increased in the ctrl-1 mutant, where ethylene-regulated pathways are constitutively a ctive, Electrophoretic mobility-shift assay and DNase I footprint anal ysis revealed that AtEBP can specifically bind to the GCC box, Interes tingly, the highest level of AtEBP expression was detected in callus t issue, where ocs elements are very active, Synergistic effects of the GCC box with ocs elements or the related G-box sequence have been prev iously observed, for example, in the ethylene-induced expression of a PR gene promoter, Our results suggest that cross-coupling between EREB P and bZIP transcription factors occurs and may therefore be important in regulating gene expression during the plant defense response.