Fungal endophytes in a 400‐million‐yr‐old land plant: infection pathways, spatial distribution, and host responses

Abstract

Summary• The Early Devonian Rhynie chert has been critical in documenting early land plant-fungal interactions. However, complex associations involving several fungi that enter into qualitatively different relationships with a single host plant and even interact with one another have not yet been detailed.• Here, we studied petrographic thin sections of the Rhynie chert plant Nothia aphylla.• Three fungal endophytes (co)occur in prostrate axes of this plant: narrow hyphae producing clusters of small spores; large spherical spores/zoosporangia; and wide aseptate hyphae that form intercellular vesicles in the cortex. Host responses on attack include bulging of infected rhizoids, formation of encasement layers around intracellular hyphae, and separation of infected from uninfected tissues by secondarily thickened cell walls.• A complex simultaneous interaction of N. aphylla with three endophytic fungi was discovered. The host responses indicate that some of the mechanisms causing host responses in extant plants were in place 400 million yr ago. Anatomical and life history features of N. aphylla suggest that this plant may have been particularly susceptible to colonization by fungi.

Endophytic fungi residing in medicinal plants have the ability to produce the same or similar pharmacologically active secondary metabolites as their hosts

“…Evidence of plant-associated microorganisms found in the fossilized tissues of land plants stems and leaves suggests that endophyte-plant associations may have evolved along with the evolution of higher land plants (Krings et al, 2007). Nearly all vascular plant species studied were found to harbor endophytic bacteria and/or fungi (Rodriguez et al, 2009;Hardoim et al, 2015).…”

An Alternative Mode of Early Land Plant Colonization by Putative Endomycorrhizal Fungi

“…The parasites, once recognized, are confined in the tissues of the rhizoidal ridge by specific or unspecific host responses, e.g., secondarily thickened cell walls. 5 Conversely, if the endomycorrhizal fungus entered the plant through surface openings, and spread out exclusively through the intercellular system, the mechanisms that might confine simultaneous parasite infections were probably much more limited.…”

“…Extramatrical hyphae of the mycorrhizal fungal enter the axes through these stomata, and spread out through the intercellular system of the hypodermis and cortex, subsequently penetrating individual cells within a well-defined region of the cortex (i.e., the mycorrhizal arbuscule-zone) to form arbuscules. 4 A recently published study 5 reports on three fungal endophytes that (co-)occur in the Rhynie chert plant Nothia aphylla. This plant consists of upright aerial axes arising from a system of non-stomatiferous, subterranean rhizomatous axes characterized by a prominent ventral rhizoidal ridge.…”

Analysis of endophytic fungi in roots of Santalum album Linn. and its host plant Kuhnia rosmarinifolia Vent.

“…Endophytic fungi have been reported to be associated with plants for over 400 million years (Krings et al, 2007), and there are about one million species existing ubiquitously in plants (Shekhawat et al, 2010). Endophytic fungi play important physiological (Malinowski et al, 2004) and ecological (Malinowski and Belesky, 2006;Tintjer and Rudger, 2006) roles in plant symbiosis, which protect their hosts from infectious agents and stressful environment by secreting bioactive secondary metabolites (Carroll and Carroll, 1978;Azevedo et al, 2000;Redman et al, 2002;Strobel, 2003;Rodriguez et al, 2004;Márquez et al, 2007).…”