Review No claim to original US government works www.newphytologist.org 1 Journal compilation © New Phytologist (2009) Blackwell Publishing Ltd Oxford, UK NPH New Phytologist 0028-646X 1469-8137 © The Authors (2009). Journal compilation © New Phytologist (2009) 2773 10.1111/j.1469-8137.2009.02773.x January 2009 01??? 17??? Tansley Review Tansley review Tansley review Tansley review Fungal endophytes: diversity and functional roles R. J. Rodriguez 1,2 , J. F. White Jr 3 , A. E. Arnold 4 and R. S. Redman 2 1 US Geological Survey, Seattle, WA, USA; 2 University of Washington, Seattle, WA, USA; 3 Rutgers University, New Brunswick, NJ, USA; 4 Division of Plant Pathology & Microbiology, Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA Contents Summary 1 I. Introduction 1 II. Clavicipitaceous endophytes (Class 1) 3 III. Nonclavicipitaceous endophytes 6 IV. Class 2 endophytes 6 V. Class 3 endophytes 8 VI. Class 4 endophytes 10 VII. Conclusions 12 Acknowledgements 13 References 13 Author for correspondence: R. J. Rodriguez Tel: +1 206 526 6596 Email: rjrodriguez@usgs.gov Received: 8 September 2008 Accepted: 20 December 2008 New Phytologist (2009) doi: 10.1111/j.1469-8137.2009.02773.x Key words: fungal taxonomy, habitat adapted symbiosis, mutualism, plant-fungal interactions, symbiosis, symbiotic continuum Summary All plants in natural ecosystems appear to be symbiotic with fungal endophytes. This highly diverse group of fungi can have profound impacts on plant communities through increasing fitness by conferring abiotic and biotic stress tolerance, increasing biomass and decreasing water consumption, or decreasing fitness by altering resource allocation. Despite more than 100 yr of research resulting in thousands of journal articles, the ecological significance of these fungi remains poorly characterized. Historically, two endophytic groups (clavicipitaceous (C) and nonclavicipitaceous (NC)) have been discriminated based on phylogeny and life history traits. Here, we show that NC-endophytes represent three distinct functional groups based on host colonization and transmission, in planta biodiversity and fitness benefits conferred to hosts. Using this framework, we contrast the life histories, interactions with hosts and potential roles in plant ecophysiology of C- and NC-endophytes, and highlight several key questions for future work in endophyte biology. I. Introduction Since the first description of symbiosis as ‘the living together of dissimilar organisms’ (De Bary, 1879), an array of symbiotic lifestyles have been defined based on fitness benefits or impacts to macroscopic hosts and microscopic symbionts (Lewis, 1985). Collectively, more than 100 yr of research suggests that most, if not all, plants in natural ecosystems are symbiotic with mycorrhizal fungi and/or fungal endophytes (Petrini, 1986). These fungal symbionts can have profound effects on