Phagocytes of the forest: Are myxomycetes defensive mutualists for host plants?

Myxomycetes are microscopic eukaryotic organisms classified within the phylum Amoebozoa. They are naked amoebae, with or without a flagellated stage in their life cycle, capable of forming a multinucleate cell (plasmodium) and producing fruiting bodies for spore dispersal. Myxomycetes are natural bacterivores and fungivores, consistently associated with plants or plant remains in terrestrial habitats. They are commonly found on decaying wood but also occur in living plants, where they may act as mutualists. Here, we propose that these microorganisms function as primary endophytic symbionts of plants, potentially protecting them from other endophytes. We comment on published studies that support this relationship and suggest that further evidence could be obtained through molecular or genomic approaches.