A novel phyllosphere resident Protomyces species that interacts with the Arabidopsis immune system.

We describe the genome contents of six Protomyces species that are pathogenic within the typical host range of the genus and a novel Protomyces strain (SC29) that was previously isolated from the phylloplane of wild Arabidopsis thaliana (Arabidopsis), an atypical host. Genome-wide phylogenetic analysis defined SC29 as a distinct Protomyces species. Analysis of gene family expansions, gene retention, and gene loss patterns among the Protomyces suggests that SC29 has recently undergone a host jump and change in lifestyle. Genomic changes in SC29 were consistent with a phylloplane lifestyle. SC29 did not cause disease on Arabidopsis, but could persist in its phylloplane, while the closely related P. inouyei does not. SC29 treated Arabidopsis exhibited enhanced immunity against Botrytis cinerea infection, associated with activation of MAPK3/6, camalexin, and SA-signalling pathways. We conclude that SC29 is a novel Protomyces species adapted to life in the Arabidopsis phylloplane.