Disturbed correlation between fungal biomass and beta-glucuronidase activity in infections of Arabidopsis thaliana with transgenic Alternaria brassicicola

Several previous studies have described the use of the bacterial uidA (beta -glucuronidase) gene to transform fungal pathogens of plants. In many cases beta-glucuronidase activity has been considered as a quantitative paramete r for the extent of development of uidA-expressing transgenic fungi in infe cted plants. Here we present evidence that this method is not applicable in all plant-pathogen interactions. In Arabidopsis plants inoculated with an uidA-expressing transgenic Alternaria brassicicola fungus, there was a good correlation between lesion development and the level of uidA mRNA whereas beta-glucuronidase activity dropped as lesions extended. This indicates tha t plant factors accumulating or released during lesion development can inte rfere with beta-glucuronidase activity in the fungus. (C) 1999 Elsevier Sci ence Ireland Ltd. All rights reserved.