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The host membrane that surrounds intracellular microbes forms a critical interface, influencing whether interactions result in mutualism or pathogenesis. While phosphoinositide identities differ between pathogen and mutualist interface membranes, it is unclear whether these are modulated during co-colonization. To address this, we generated Nicotiana benthamiana plants expressing biosensors for phosphatidylinositol 4-phosphate (PI4P) and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ) and imaged root colonization by the pathogenic oomycete Phytophthora palmivora and the mutualistic fungus Funneliformis mosseae . Binary host-microbe interactions revealed distinct patterns: PI(4,5)P 2 was tip enriched at mutualist structures but evenly distributed around pathogen structures, while PI4P was largely absent from pathogen-associated membranes but was present at mutualist interfaces. Strikingly, co-colonization altered host membrane identity, triggering PI4P recruitment at pathogen haustoria and enhanced resistance to P . palmivora . These findings reveal that phosphoinositide signatures distinguish pathogenic and mutualistic interfaces and are dynamically remodeled during co-colonization, likely influencing interaction outcomes.
Guyon et al. (Mon,) studied this question.