Ontogenetic transition from specialized root hairs to specific root-fungus symbiosis in the dominant Mediterranean seagrass Posidonia oceanica

Abstract

Terrestrial plants typically take up nutrients through roots or mycorrhizae while freshwater plants additionally utilize leaves. Their nutrient uptake may be enhanced by root hairs whose occurrence is often negatively correlated with mycorrhizal colonization. Seagrasses utilize both leaves and roots and often form root hairs, but seem to be devoid of mycorrhizae. The Mediterranean seagrass Posidonia oceanica is an exception: its adults commonly lack root hairs and regularly form a specific association with a single pleosporalean fungus. Here we show that at two sites in the southern Adriatic, all its seedlings possessed abundant root hairs with peculiar morphology (swollen terminal parts) and anatomy (spirally formed cell walls) as apparent adaptations for better attachment to the substrate and increase of breaking strain. Later on, their roots became colonized by dark septate mycelium while root hairs were reduced. In adults, most of terminal fine roots possessed the specific fungal association while root hairs were absent. These observations indicate for the first time that processes regulating transition from root hairs to root fungal colonization exist also in some seagrasses. This ontogenetic shift in root traits may suggests an involvement of the specific root symbiosis in the nutrient uptake by the dominant Mediterranean seagrass.

Characterization of the mycobiome of the seagrass,Zostera marina, reveals putative associations with marine chytrids

“…We found that the Glomerellales , particularly a Colleotrichum species (SV10), was abundant in the lower 10 inches of leaf tissue and enriched on the leaves relative to other sample types. DSE, particularly members of the Pleosporales, have previously been observed associating with seagrasses (Borovec and Vohník, 2018; Gnavi et al, 2014; Panno et al, 2013; Torta et al, 2015; Vohník et al, 2015, 2016, 2017, 2019). In the mediteranean seagrass, Posidonea , it has been observed that the abundance of the dominant root associated fungi, a Pleosporales species ( Posidoniomyces atricolor gen. et sp.…”

“…In the mediteranean seagrass, Posidonea , it has been observed that the abundance of the dominant root associated fungi, a Pleosporales species ( Posidoniomyces atricolor gen. et sp. nov.), is associated with changes in root hair morphology and can form ecto-mycorrhizal-like structures suggesting a close seagrass-fungi symbiosis (Borovec and Vohník, 2018; Vohník et al, 2016, 2017, 2019).…”

“…In contrast to their apparent lack of mycorrhizal associations, some studies of seagrasses have observed associations with novel fungal endophytes similar to dark septate endophytes (DSE) common in land plants (Borovec and Vohník, 2018; Torta et al, 2015; Vohník et al, 2015, 2016, 2017, 2019). DSE are a morphology based type and not a phylogenetic group, and are largely uncharacterized.…”

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

“…The most well described of these DSE associations is between the mediteranean seagrass, Posidonia oceanica, and its dominant root-associated fungus, Posidoniomyces atricolor. This Pleosporales member has been found associated with changes in root hair morphology and can form ecto-mycorrhizal-like structures (Vohník et al, 2016(Vohník et al, , 2017(Vohník et al, , 2019Borovec & Vohník, 2018). Here, although we isolated seven members of the Pleosporales, none appeared to be close relatives to Posidoniomyces atricolor.…”

“…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.…”