LAUSR

Carbohydrates such as fructans are naturally derived molecules that can be implemented in priming or defence stimulation, providing new strategies for crop protection against biotic stress. Chicory is a model plant for fructan research and a crop with many known health benefits. Using the chicory-Botrytis cinerea pathosystem, we tested the effectiveness of fructan-induced immunity, focussing on different plant and microbial fructans. Sugar dynamics were followed after priming and subsequent pathogen infection. Our data indicate that many higher plants may detect extracellular levan oligosaccharides (LOS) from microbial origin, while chicory also detects extracellular fructooligosaccharides (FOS) from endogenous origin, thus differing from previous fructan priming studies. No clear positive effects were observed for inulin or mixed-type fructans. An elicitor-specific ROS burst was observed for sulfated LOS, while FOS and LOS behaved as a real priming agent. In addition, a direct antifungal effect was observed for sulfated LOS. Intriguingly, LOS priming led to a temporary increase in apoplastic sugar levels, mainly glucose, which can trigger downstream responses. Total sugar and starch content in total extracts of LOS-primed leaves were higher after leaf detachment, indicating these leaves can maintain their metabolic activity. Our results indicate the importance of balancing intra- and extracellular sugar levels (osmotic balance) in light of sweet immunity pathways.