Root-Colonizing Endophytic Fungi of the Dominant Grass Stipa krylovii From a Mongolian Steppe Grassland

Abstract

In several terrestrial ecosystems such as grasslands, plants live together with various root-colonizing dark septate endophytes (DSEs), fungi that are relatively frequent colonizers of healthy belowground tissues of plants in these environments. They are important members of the plant microbiota and may have various effects on plant survival under different stress conditions; however, their general functions in relation to plants and the greater ecosystem remain elusive. Although an increasing number of studies has been published focusing on DSEs in Asian grasslands, our knowledge is limited. Especially in Mongolia, where the steppe region represents a significant area, information is not available on these root colonizers. In this study, we aimed to characterize DSEs of a common dominant gramineous plant species, Stipa krylovii in a semiarid grassland of Mongolia. Root samples were collected in a natural steppe and were processed for isolation of fungal endophytes. For molecular identification of the isolates, the internal transcribed spacer (ITS) region of the nrDNA was obtained for all the isolates investigated; furthermore, the partial translation elongation factor 1-α (TEF) gene and large subunit (LSU) and small subunit (SSU) of rDNA were also amplified and sequenced in case of representative isolates. In vitro tests were used to examine the rough symbiotic nature of the fungi, and root colonization was visualized. A majority of the 135 isolates examined in detail was found to belong to several orders of Ascomycota (110 isolates) and some to Basidiomycota (25 isolates). A significant number of the isolates represented presumably novel taxa, and dominant similarities of the lineages have been found with relatively frequent and known grass root endophytes of semiarid areas in other geographic regions. These endophytes included Periconia macrospinosa, Microdochium bolley, and Darksidea, the genus of which comprised one fourth of the isolates. We found numerous lineages, which have been detected not only from Asian steppe ecosystems, but also from prairies in North America and sandy grasslands in Europe. Therefore, our results strengthen the hypothesized worldwide presence of a common and dominant core group of a DSE community in arid and semiarid grasslands.

Two pleosporalean root-colonizing fungi, Fuscosphaeria hungarica gen. et sp. nov. and Delitschia chaetomioides, from a semiarid grassland in Hungary

“…Although based on the results of isolation techniques, these two species are not among the dominant lineages of root-associated fungi (e.g., Knapp et al 2012Knapp et al , 2015, sequences of both species were found in our databases of the ITS-based metabarcoding study of the soil fungal community in different sites of the grassland near Fülöpháza (Vajna, Knapp, and Kovács, unpublished results), strengthening the idea of their common presence in this semiarid area. Further investigations of non-pathogenic root colonizers of gramineous plants may reveal their broader occurrence on semiarid grasslands, which was found for several root endophytes (Knapp et al 2019).…”

“…The order Pleosporales is one of the most common orders in grassland ecosystems, comprising a plethora of grass root endophytes (Zhang et al 2012;Jumpponen et al 2017). Several common pleosporalean DSE fungi have been studied to date, including Darksidea species (Knapp et al 2015(Knapp et al , 2019 and the relatively well-studied Periconia macrospinosa (see Mandyam et al 2010;Knapp et al 2018). Pleosporales includes an increasing number of root endophytic species and genera; for example, in the last year only, several novel DSE lineages were investigated and formally described, such as Alfoldia vorosii (Crous et al 2019), Laburnicola rhizohalophila (Yuan et al 2019), Kiskunsagia ubrizsyi (Crous et al 2019), and Posidoniomyces atricolor (Vohník et al 2019).…”

“…This artificial group of fungi also comprises pathogens and saprobes, which, at some point in their life cycle, colonize plant tissues without causing symptoms of tissue damage (Wilson 1995); and it seems that in this group, species commonly considered as endophytes are rather pathogenic (Schlegel et al 2016) or possess an expanded repertoire of genes linked with saprobic abilities (Knapp et al 2018). These root colonizers are relatively frequent in arid and semiarid grasslands worldwide (Mandyam and Jumpponen 2005), where they inhabit healthy roots of different grass species (Porras-Alfaro et al 2008;Knapp et al 2012Knapp et al , 2019. They are generally ascomycetes and usually have pigmented hyphae, which is why they are commonly called dark septate endophytes (DSE) (Jumpponen and Trappe 1998;Porras-Alfaro and Bayman 2011).…”

“…is one of the dominant grass species in sandy areas, such as the semiarid open sandy grasslands of the interfluves of the Danube and Tiscia (Szabó et al 2017), which are also inhabited by a wide spectrum of rootcolonizing non-mycorrhizal fungi (Knapp et al 2012(Knapp et al , 2015 as well as arbuscular mycorrhizae (Endresz et al 2013). Similar to other grasses dominating certain ecosystems across the temperate region, such as Andropogon, Bouteloua, Festuca, and Stipa species (e.g., Porras-Alfaro et al 2008;Mandyam et al 2010;Knapp et al 2012Knapp et al , 2019 F. vaginata accommodates a core community of root-associated fungi, which was concluded using isolation-based techniques (Khidir et al 2010;Knapp et al 2012Knapp et al , 2019.…”

Unravelling the Role of Melanin in Cd and Zn Tolerance and Accumulation of Three Dark Septate Endophytic Species

“…They have been observed in the roots of more than 600 plant species spanning 100 plant families [2]. DSEs have a wide geographical distribution (e.g., arctic, boreal, alpine, temperate forest, or tropical ecosystems) and display strong abilities to tolerate a range of environmental stresses (e.g., drought, salinity, pollution) [2][3][4][5].…”