A structural homologue of the plant receptor D14 mediates responses to strigolactones in the fungal phytopathogen Cryphonectria parasitica

Strigolactones (SLs) are plant hormones and important signalling molecules required to promote arbuscular mycorrhizal (AM) symbiosis. While in plants an a/b-hydrolase, DWARF14(D14), was shown to act as a receptor that binds and cleaves SLs, the fungal receptor for SLsis unknown. Since AM fungi are currently not genetically tractable, in this study, we used the fungalpathogen Cryphonectria parasitica, for which gene deletion protocols exist, as a model, as wehave previously shown that it responds to SLs. By means of computational, biochemical andgenetic analyses, we identified a D14 structural homologue, CpD14. Molecular homology modelling and docking support the prediction that CpD14 interactswith and hydrolyses SLs. The recombinant CpD14 protein shows a/b hydrolytic activity in vitro against the SLs synthetic analogue GR24; its enzymatic activity requires an intactSer/His/Asp catalytic triad. CpD14 expression in the d14-1 loss-of-function Arabidopsisthaliana line did not rescue the plant mutant phenotype. However, gene inactivation byknockout homologous recombination reduced fungal sensitivity to SLs. These results indicate that CpD14 is involved in SLs responses in C. parasitica and strengthenthe role of SLs as multifunctional molecules acting in plant-microbe interactions.