Phakopsora pachyrhizi induces defense marker genes to necrotrophs in Arabidopsis thaliana

• Germination fluid of biotroph Phakopsora pachyrhizi causes accumulation of marker PDF1.2.
• PDF1.2-eliciting activity can be abolished by autoclaving and trypsin digestion.
• PDF1.2-eliciting activity is of (glyco)proteinaceous nature.

Phakopsora pachyrhizi is a rust fungus that causes Asian soybean rust disease. In the nonhost plant Arabidopsis thaliana penetrated epidermis cells initiate cell death associated with mRNA transcript accumulation of PDF1.2, a marker gene for defense against necrotrophic pathogens. PDF1.2 activation occurred after both inoculation of A. thaliana leaves with P. pachyrhizi spores and upon their treatment with spore germination fluid, suggesting PDF1.2 activation by secreted fungal effectors. These are likely (glyco)proteins. Together, P. pachyrhizi seems to feign a necrotroph pathogen during early stages of infection to circumvent plant defense to biotrophs.