Communities of Cultivable Root Mycobionts of the Seagrass Posidonia oceanica in the Northwest Mediterranean Sea Are Dominated by a Hitherto Undescribed Pleosporalean Dark Septate Endophyte

Abstract

Seagrasses, a small group of submerged marine macrophytes, were reported to lack mycorrhizae, i.e., the root-fungus symbioses most terrestrial plants use for nutrient uptake. On the other hand, several authors detected fungal endophytes in seagrass leaves, shoots, rhizomes, and roots, and an anatomically and morphologically unique dark septate endophytic (DSE) association has been recently described in the roots of the Mediterranean seagrass Posidonia oceanica. Nevertheless, the global diversity of seagrass mycobionts is not well understood, and it remains unclear what fungus forms the DSE association in P. oceanica roots. We isolated and determined P. oceanica root mycobionts from 11 localities in the northwest Mediterranean Sea with documented presence of the DSE association and compared our results with recent literature. The mycobiont communities were low in diversity (only three species), were dominated by a single yet unreported marine fungal species (ca. 90 % of the total 177 isolates), and lacked common terrestrial and freshwater root mycobionts. Our phylogenetic analysis suggests that the dominating species represents a new monotypic lineage within the recently described Aigialaceae family (Pleosporales, Ascomycota), probably representing a new genus. Most of its examined colonies developed from intracellular microsclerotia occupying host hypodermis and resembling microsclerotia of terrestrial DSE fungi. Biological significance of this hitherto overlooked seagrass root mycobiont remains obscure, but its presence across the NW Mediterranean Sea and apparent root intracellular lifestyle indicate an intriguing symbiotic relationship with the dominant Mediterranean seagrass. Our microscopic observations suggest that it may form the DSE association recently described in P. oceanica roots.

Rare phytomyxid infection on the alien seagrass Halophila stipulacea in the southeast Aegean Sea

“…Sample preparation and microscopic procedures followed those described in Vohník et al (2015) and Vohník et al (2016). In brief, macro-photographs of the phytomyxid infection were taken using an Olympus SZX12 stereomicroscope equipped with an Olympus DP70 camera.…”

All small things considered: the diversity of fungi, bacteria and oomycota isolated from the seagrass,Zostera marina

“…Dark septate endophytes (DSE), particularly members of the Pleosporales within the Dothideomycetes (Figure 6), have been observed to form associations with several seagrass species (Panno et al, 2013;Gnavi et al, 2014;Vohník et al, 2015Vohník et al, , 2016Vohník et al, , 2017Vohník et al, , 2019Borovec & Vohník, 2018;Hurtado-McCormick et al, 2019). DSE are a morphological, not phylogenetic (e.g.…”

“…Additionally, we wanted to place the Z. marina associated fungal isolates in the context of the phylogenetic diversity of available other seagrass-associated fungal isolates. To this end, we performed a literature search to obtain, to our knowledge at the time of the search, all available 28S rRNA sequences obtained from seagrass associated fungal isolates for inclusion in phylogenetic analyses (Table S3) (Sakayaroj et al, 2010;Gnavi et al, 2014;Vohník et al, 2016Vohník et al, , 2019Supaphon et al, 2017). Finally, to provide a further framework for these phylogenies, as well as appropriate outgroup taxa, we downloaded the available 28S rRNA sequences previously used in James et al (2006a,b) (Table S4).…”

“…In an attempt to cultivate a wide diversity of fungal isolates, we used a variety of media types including several which had been used previously to isolate fungi from seagrasses (e.g. PDA (Sakayaroj et al, 2010;Vohník et al, 2016;Supaphon et al, 2017), GPYA (Panno et al, 2013), MEA (Torta et al, 2015)). A total of 108 fungal isolates were obtained, with the majority cultured from Z. marina leaf tissue (n = 50), resulting in a range of morphological diversity (Figure 1).…”

“…Culture-based studies have found fungi associated with leaves, roots and rhizomes of seagrasses, but there is little agreement between studies about the taxonomic composition of these communities within and between seagrass species (Newell, 1981;Kuo, 1984;Cuomo et al, 1985;Devarajan & Suryanarayanan, 2002;Sakayaroj et al, 2010;Mata & Cebrián, 2013;Shoemaker & Wyllie-Echeverria, 2013;Supaphon et al, 2013Supaphon et al, , 2014Supaphon et al, , 2017Panno et al, 2013;Kirichuk & Pivkin, 2015;Venkatachalam, 2015;Venkatachalam et al, 2015;Torta et al, 2015;Ling et al, 2015;Vohník et al, 2016). Recently culture-independent studies of seagrassassociated fungi have more thoroughly investigated the diversity of these microorganisms and highlighted a need to further understand factors affecting their biogeography and community dynamics (Wainwright et al, 2018(Wainwright et al, , 2019Hurtado-McCormick et al, 2019;Ettinger & Eisen, 2019).…”