DsEcp2-1 is a polymorphic effector that restricts growth of Dothistroma septosporum in pine

The detrimental effect of fungal pathogens on forest trees is an increasingly important problem that has implications for the health of our planet. Despite this, the study of molecular plant-microbe interactions in forest trees is in its infancy, and very little is known about the roles of effector molecules from forest pathogens. Dothistroma septosporum causes a devastating needle blight disease of pines, and intriguingly, is closely related to Cladosporium fulvum, a tomato pathogen in which pioneering effector biology studies have been carried out. Here, we studied D. septosporum effectors that are shared with C. fulvum, by comparing gene sequences from global isolates of D. septosporum and assessing effector function in both host and non-host plants. Many of the effectors were predicted to be non-functional in D. septosporum due to their pseudogenization or low expression in planta, suggesting adaptation to lifestyle and host. Effector sequences were polymorphic among a global collection of D. septosporum isolates, but there was no evidence for positive selection. The DsEcp2-1 effector elicited cell death in the non-host plant Nicotiana tabacum, whilst D. septosporum DsEcp2-1 mutants showed increased colonization of pine needles. Together these results suggest that DsEcp2-1 might be recognized by an immune receptor in both angiosperm and gymnosperm plants. This work may lead to the identification of plant targets for DsEcp2-1 that will provide much needed information on the molecular basis of gymnosperm-pathogen interactions in forests, and may also lead to novel methods of disease control.