Microfungal endophytes in roots

Abstract

A wide range of ascomycetous microfungi inhabits roots without forming the anatomical features typical of mycorrhizas or causing overt signs of pathogenesis. The most-studied taxa have darkly pigmented hyphal walls and are referred to as "dark septate endophytes" (DSE). We provide a dichotomous key and annotated descriptions for a cross-section of the most common dark septate endophytes. The term DSE is sometimes used to imply taxonomic and physiological similarity even though a diverse range of root endophytic taxa form pigmented hyphae. Among these, Phialocephala fortinii Wang & Wilcox is a well-known representative; it is widespread, easily observed in roots, and readily grown in culture and with plants. Nevertheless, the basis of its symbiotic relationship with plants remains ambiguous. It may be a weak pathogen, a saprotroph on senescent root tissues, or a mutualist. More detailed studies of interactions between identified taxa of microfungal endophytes and host plants are necessary to elucidate the functional basis of these symbioses; it may be necessary to look beyond the paradigms of traditional mycorrhizal and pathogenic associations to understand the ecological roles of these fungi. Reports of cryptic speciation in Phialocephala fortinii emphasize the need for accurate identification of isolates of microfungal endophytes used in experiments.Key words: dark septate endophytes (DSE), Phialocephala fortinii, mycorrhiza, fungus–host interactions, fungi.

Arabidopsis thaliana model system reveals a continuum of responses to root endophyte colonization

“…3). These results suggest that DSE are probably weak parasites supporting some earlier conclusions (Addy et al 2005, Alberton et al 2010, although some strains may behave as mutualists. However, a recent meta-analysis (Newsham 2011) suggested that the DSE symbioses tended to be positive, though mainly so if nitrogen was supplied in organic forms.…”

“…Although many DSE fungi form similar morphological structures in the host roots (Jumpponen & Trappe 1998, Rodriguez et al 2009), they are taxonomically unrelated, vary in ecological or physiological functions and lead to variable host responses (Addy, Piercey & Currah 2005, Alberton, Kuyper & Summerbell 2010, Newsham 2011, Tellenbach, Grünig & Sieber 2011, Knapp, Pintye & Kovacs 2012. Our earlier studies in the tallgrass prairie concluded that while grasses overall tend to be colonized to a greater extent and respond more positively to DSE colonization, forbs also range from increased to no response to decreased biomass accumulation in their response to DSE fungi (Mandyam, Fox & Jumpponen 2012).…”

“…To exemplify, many Arabidopsis resources, including whole genome microarrays, easy access to ecotypes and/or accessions of Arabidopsis, mutants of many physiological pathways, and abundant literature are available for exploitation to dissect the DSE symbiosis at the whole plant, genetic, molecular or physiological level (see Buell & Last 2010 Mutualism-parasitism continuum paradigm has been used for mycorrhizal (Francis & Read 1995, Johnson, Graham & Smith 1997, Jones & Smith 2004, as well as nonmycorrhizal root and foliar endophyte associations (Saikkonen et al 1998, Schulz & Boyle 2005, Schulz 2006) to account for variable host responses. Considerable uncertainty exists on whether DSE should be considered parasites, mutualists, or simply casual inhabitants of the root environment (Jumpponen 2001, Addy et al 2005, Mandyam & Jumpponen 2005.…”

Paleomycology of the Princeton Chert II. Dark-septate fungi in the aquatic angiospermEorhiza arnoldiiindicate a diverse assemblage of root-colonizing fungi during the Eocene

“…On the basis of these morphological characters, it is unlikely that the fossils share an affinity with the basidiomycetous Rhizoctonialike soil pathogens, but hyphal features alone do not permit us to more precisely identify them, especially because monilioid growth is common to many fungi that colonize vascular plants, including both plant pathogens and endophytes (Melin 1923, Parmeter and Whitney 1970, Currah et al 1988. Unambiguous identification of sterile mycelia in living fungi depends upon observing their association with conidial or sexual phases, characterizing substrate utilization, or molecular taxonomy (Addy et al 2005, García et al 2006. …”

Potential of the Endophytic Fungus Phialocephala fortinii Rac56 Found in Rhodiola Plants to Produce Salidroside and p-Tyrosol

“…Several reports have shown that P. fortinii exhibits versatile capacities of promoting elemental nitrogen (N) and phosphorus (P) absorption by host plants [25] and synthesizing glucose [26] by co-existing with host roots. Further, P. fortinii have also been shown to aid the enhancement of disease resistance in hosts, controlling Verticillium yellows in Chinese cabbage [27], the capacity to produce chemicals such as hydroxamate siderophore [28] and other enzymes in improving host resistance and absorption of nutrients, for example, production of extracellular aryl sulfatase to decompose aryl sulphates [29]. All of these abilities, along with its ability to produce SAL and TYR, suggest that P. fortinii plays a key role in symbiosis with host plants.…”