Induction of Cell Death in Transgenic Plants Expressing a Fungal Glucose Oxidase

Abstract

Hydrogen peroxide (H2O2) has been implicated in the induction of plant defense genes and programmed cell death. Expression of a chimeric fungal glucose oxidase (GO) gene driven by a pathogen- and wound-inducible promoter was evaluated in transgenic tobacco and canola as a possible tool for engineering plant cell death and defense gene induction. Expression of this gene under the control of a peroxidase gene promoter resulted in the accumulation of relatively low levels of H2O2 in the young leaves of transgenic tobacco plants and this was not sufficient to cause any visible cell death and defense gene induction as measured by PR-1a mRNA induction. Older leaves of transgenic tobacco plants, however, exhibited visible necrotic lesions and constitutively expressed PR-1a mRNA when grown under high light conditions. Inoculation of cotyledons of control and transgenic canola with Leptosphaeria maculans resulted in rapid cotyledon senescence in the transgenic plants. Strong activators of the peroxidase promoter, i.e., wounding and inoculation of transgenic plants with Cercospora nicotianae, were not sufficient to trigger any additional visible cell death in transgenic tobacco plants, compared with controls. However, when exogenous glucose was supplied to transgenic tissue, massive cell death and PR-1a gene induction were observed in tobacco. Exogenously applied salicylic acid further increased the rate and extent of cell death. Our results suggest that efficacy of GO expression for the induction of cell death is restricted by glucose supply in the plants and are consistent with a role for salicylic acid in the potentiation of plant cell death by H2O2.