Exploring fern pathosystems and immune receptors to bridge gaps in plant immunity.

Land plants include angiosperms, gymnosperms, bryophytes, lycophytes, and ferns, each of which may deploy distinct strategies to resist pathogens. Here, we investigate fern-pathogen interactions by characterizing novel pathosystems and analyzing the diversity of fern immune receptors. A collection of fern species was inoculated with a diverse set of filamentous microbes, and disease symptoms were assessed. We further leveraged published genome mining tools to analyse the diversity of RECEPTOR-LIKE KINASES, RECEPTOR-LIKE PROTEINS (RLKs/RLPs) and NUCLEOTIDE-BINDING AND LEUCINE-RICH REPEATS (NLRs), along with key immune signalling components, in ferns. Our results reveal that ferns exhibit a range of responses to pathogens, including putative non-host resistance and more specific resistance mechanisms. Among ten ferns tested, Pteris vittata displays the broadest spectrum of pathogen compatibility. Genome mining indicates that ferns encode a diverse repertoire of putative immune receptors, antimicrobial peptides, and mediators of systemic acquired resistance. Ferns possess numerous RLKs/RLPs, resembling those required for cell-surface immunity in angiosperms. They also encode diverse NLRs, including sub-families lost in flowering plants. These findings provide insights into disease resistance evolution and open promising perspectives for crop protection strategies.