Thale Cress Pickiness
It was long thought that the sole role of the immune system was to distinguish friend from foe and vanquish the unwanted. An immune system is instead more a microbiome management system.
While most plants employ a mycorrhizal mesh to get the phosphate and other minerals they need, thale cress does not. Instead, the plant selectively allows the fungus Colletotrichum tofieldiae around its roots only when it needs help mining minerals from the soil. If phosphate is plentiful, the fungus is rejected by the plant’s immune system.
The thale cress plant controls its interaction with its tenant by linking its immune system to a sensor for phosphate availability. It’s a fantastically well-regulated system. A foe is recognized as such only in specific circumstances. ~ German botanist Paul Schulze-Lefert
The beneficial interaction between Colletotrichum and thale cress is surprising, in that this fungal family is almost everywhere a plant pathogen. But the central plateau of Spain, where this selective mutualism occurs, is a difficult environment, with scant soluble phosphate in the soil. Thale cress managed to strike a deal because otherwise it could not survive, and the fungus would go wanting.
The mutual coexistence is beneficial to both partners, but only as long as the right conditions prevail. ~ Paul Schulze-Lefert
