Unraveling the Dark Septate Endophyte Functions: Insights from the Arabidopsis Model
The global occurrence of plant root-associated fungal endophytes and their great abundance in many habitats necessitate studies to decipher their potential functions. Improved understanding of the basic endophyte ecology including host range, host prefere
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Unraveling the Dark Septate Endophyte Functions: Insights from the Arabidopsis Model Keerthi Mandyam and Ari Jumpponen
Abstract
The global occurrence of plant root-associated fungal endophytes and their great abundance in many habitats necessitate studies to decipher their potential functions. Improved understanding of the basic endophyte ecology including host range, host preference, and host responses to endophyte colonization has been made possible through populations of endophytes (e.g., Periconia macrospinosa and Microdochium sp.) isolated from North American native tallgrass prairie. The recent demonstration of the endophyte symbiosis of the model plant Arabidopsis thaliana has provided additional tools to further elucidate the ecology of these endophytes. The availability of a large number of Arabidopsis ecotypes and mutants, microarrays, and databases allows the molecular dissection of endophyte symbiosis to better understand the importance of fungal endophytes in host nutrient uptake, defenses, and/or responses to pathogens and stress. In this chapter, we discuss the ecology and functions of endophytic fungi through experiments utilizing the Arabidopsis model system. We draw parallels with another deeply dissected Piriformospora indica root endophyte symbiosis, which has been demonstrated to promote growth of model and non-model plants.
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Introduction
Plants typically host a variety of microbial endophytes. Plant roots in particular maintain broad assortments of microbial communities exemplified by actinobacteria, plant growth-promoting K. Mandyam • A. Jumpponen (*) Division of Biology, Kansas State University, Ackert Hall, Manhattan, KS 66506, USA e-mail: [email protected]
rhizobacteria (PGPR), nitrogen-fixing rhizobia, as well as fungi including a variety of mycorrhizal and endophytic fungi. Some fungal endophytes (e.g., clavicipitaceous foliar endophytes) have been the subject of rigorous investigations, and much is understood about their role as plant symbionts largely owing to their potential applications with crop or forage species. However, dark septate endophyte (DSE) fungi are an exception, and despite their similarities with mycorrhizal fungi – global occurrence, high colonization
V.C. Verma and A.C. Gange (eds.), Advances in Endophytic Research, DOI 10.1007/978-81-322-1575-2_6, © Springer India 2014
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rates, and broad host range (Jumpponen and Trappe 1998a; Jumpponen 2001) – there is a conspicuous lack of substantial data on their ecological significance (Rodriguez et al. 2009). Several factors may have contributed to the paucity of information on the DSE fungi. First, the DSE fungi have been notoriously difficult to identify. Most do not produce sexual stages, and many fail to produce asexual spores even after induced conidiogenesis. This inevitably leads to lack of morphological traits to assist in taxonomic assignment of these fungi. Phialocephala fortinii is perhaps the most well-known DSE fungus (Addy et al. 2005). Although it has been morphologically defined, the taxon likely co
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