Plant-fungal chemical feedbacks mediate host affinity and functional roles of endophytes

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Natalie S. Christian, Biology, University of Louisville, Louisville, KY, Brian E. Sedio, Department of Integrative Biology, University of Texas at Austin, Austin, TX, Ximena Florez-Buitrago, Enith I. Rojas, John W. Schroeder and Edward Allen Herre, Smithsonian Tropical Research Institute, Panama, Luis A. Ramírez-Camejo and Luis C. Mejía, Center for Biodiversity and Drug Discovery, Institute for Scientific Research and High Technology Services (INDICASAT-AIP), Panama, Sage Palmedo and Autumn Rose, Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ

Background/Question/Methods
Interactions between fungal endophytes and their host plants represent model systems for identifying the factors that affect community assembly of host-associated microbiomes. Here we investigated the role of secondary chemistry in mediating host-endophyte interactions using Theobroma cacao (cacao) and Psychotria spp. as hosts. First, we used culture-based methods to survey endophytes in co-occurring Psychotria species. Then we used liquid chromatography-tandem mass spectrometry to examine how endophyte community composition correlated with foliar secondary chemistry in the same species. Finally, we tested how inoculation with live and heat-killed endophytes affected the cacao chemical profile.
Results/Conclusions
Despite sharing a common environment and source pool for endophyte spores, Psychotria leaf endophyte communities showed high host affinity that correlated with host differences in leaf chemistry. In T. cacao, inoculation with live and heat-killed endophytes resulted in changes to the cacao chemical profile that were not found in uninoculated plants or pure fungal cultures, suggesting that endophyte colonization induced changes in secondary chemical profiles of their host. Collectively our results indicate feedbacks between plant secondary chemistry and foliar endophyte communities, in which host chemistry acts as a filter that influences endophyte community assembly, and colonization by endophytes subsequently induces changes in the host chemical landscape.