Thanks to a fungus, the medicinal plant ribwort plantain gains a higher concentration of the defensive compound catalpol. The increase in catalpol gives the plant better protection against pests. In the study, the research team worked with arbuscular mycorrhizal fungi. These are known to colonize the roots of land plants. The plants benefit from this because the fungus provides them with nutrients and minerals. However, are the impacts of this marriage of convenience with the fungus on plant chemistry equal for all plants? That is what the researchers wanted to find out.