ABA-REGULATED PROMOTER ACTIVITY IN STOMATAL GUARD-CELLS

CDeT6-19 is an ABA-regulated gene which has been isolated from Crarero stigma plantagineum. The CDeT6-19 gene promoter has been fused to the beta-glucuronidase reporter gene (GUS) and used to stably transform Ar abidopsis thaliana and Nicotiana tabacum. This construct has been show n to be expressed in stomatal guard cells and often in the adjacent ep idermal cells of both species in response to both exogenous ABA and dr ought stress. These results indicate that the stomatal guard cell is c ompetent to relay an ABA signal to the nucleus. In contrast GUS expres sion directed by the promoter from a predominantly seed-specific, ABA- regulated gene, Em, or the promoter from the ABA-regulated CDeT27-45 g ene is not detectable in the epidermal or guard cells of tobacco or Ar abidopsis in response to ABA. The fact that not all ABA-regulated gene promoters are active in stomatal guard cells suggests that effective transduction of the signal is dependent upon particular regions within the gene promoter or that guard cells lack all or part of the specifi c transduction apparatus required to couple the ABA signal to these pr omoters. This suggests that there are multiple ABA stimulus response c oupling pathways. The identification of a regulatory sequence from an ABA-induced gene which is expressed in stomatal guard cells creates th e possibility of examining the role of Ca2+ and other second messenger s in ABA-induced gene expression.