Activation of Gene Expression upon Infection with the Vascular Pathogen Verticillium longisporum

Verticillium longisporum is a vascular pathogen that enters its hosts (Brassicaceae, in particular oilseed rape) through the roots. After having reached the xylem vessels it spreads systemically to the shoot. Due to the growing demand for oil crops as sources for nutritional oils and bio-fuels, novel strategies to limit the spread of V. longisporum are needed. Since these can be based on the molecular mechanisms of defense responses, we have started to investigate the interaction between V. longisporum and the model plant Arabidopsis thaliana.

We have found that the fungus cannot complete its life cycle in plants, which lack the receptor of the plant defense hormone jasmonyl-isoleucine (JA-Ile), COI1. Surprisingly, the disease promoting COI1 function acts independently from its ligand JA-Ile or any fungal-derived JA-Ile mimics. This novel COI1 activity is required only in the root, but it influences the proliferation of the fungus in the shoot. Thus, we postulate that roots synthesize a mobile signal which is transported to the shoot to increase susceptibility.

Our aim is to unravel further components of the novel COI1-dependent but JA-Ile-independent signaling pathway and to identify the nature of the mobile signal which is generated in a COI1-dependent manner.