OCS ELEMENT PROMOTER SEQUENCES ARE ACTIVATED BY AUXIN AND SALICYLIC-ACID IN ARABIDOPSIS

ocs elements are a group of promoter elements that have been exploited by two distinct groups of plant pathogens, Agrobacterium and certain viruses, to express genes in plants. We examined the activity of single and multiple ocs elements linked to a minimal plant promoter and the uidA reporter gene in transgenic Arabidopsis. Beta-glucuronidase activity was detected only in root tips and in callus tissue after auxin treatment. A more sensitive assay revealed that auxin treatment also increased ocs element activity in aerial parts of the plant, although the absolute levels of ocs element activity were greater in roots. The response of ocs elements to exogenous auxin began within 1 h. Salicylic acid, a disease-resistance signal in plants, also increased ocs element activity in both roots and aerial parts of the plant. The question of whether the induction in ocs element activity is mediated through auxin and/or salicylic acid signal transduction pathways or is part of a more general stress response is discussed.