A Novel Pathosystem With the Model Plant Arabidopsis thaliana for Defining the Molecular Basis of Taphrina Infections.

Plant-associated yeasts modulate host immunity to promote or prevent disease. Mechanisms of yeast perception by the plant innate immune system remain unknown, with progress hindered by lack of a model system with the model plant Arabidopsis thaliana (Arabidopsis). A yeast strain of Taphrina tormentillae, named M11, was previously isolated from wild Arabidopsis. Taphrina have been found on many non-host plants, and their complex ecology remains understudied. Here, the interaction of M11 with Arabidopsis was characterised. Infection of Arabidopsis with the birch pathogen T. betulina, used as a non-host control, triggered typical defence activation features but did not multiply, demonstrating Arabidopsis had immunity against a non-adapted yeast. M11 triggered attenuated defence activation features, grew in planta, and caused subtle but clear leaf deformation symptoms, demonstrating it is pathogenic. M11 was widely distributed in environmental sequencing data and found on multiple non-host plants, suggesting Taphrina play previously unrecognised ecological roles on multiple plant species. M11 genome features involved in host interaction were analysed, and potential immune stimulatory molecules in chitin-free cell walls were identified. A pilot screen demonstrated the utility of reverse genetics with Arabidopsis and identified that the BAK1 co-receptor is involved in the perception of M11 Taphrina cell walls.