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"Sebacinales Everywhere" – fungi that live in special symbioses

Researchers have a created a specific type of endophytic symbiosis between fungi and plant roots that does not lead to visible mycorrhiza. In addition, a team of biologists from Tübingen along with international partners has discovered that Sebacinales (fungi) are ubiquitous endophytes of plant roots.

Fungi of the order Sebacinales are extremely inconspicuous. They are involved in a puzzling variety of mutualistic plant-fungal symbioses, so-called mycorrhizae. However, it has been known for quite some time that not all Sebacinales fit into this definition. Laboratory experiments with a few species enabled researchers to create symbioses between fungi and plant roots and showed that the fungi were symptomless endophytes. In contrast to typical mycorrhiza, the sebacinalean fungi did not lead to visible mycorrhiza on the roots of plants nor could any other microscopic symptoms of mycorrhizal growth be observed. Researchers became aware of this special type of symbiosis because of its capacity to enhance plant growth and increase the resistance of the plant hosts to abiotic stress factors and parasitic fungi.

Spore-forming cells (basidia) of Sebacina dimitica © Franz Oberwinkler

Investigations of wild plant root specimens have led to surprising discoveries: endophytic Sebacinales are ubiquitous; they are found in highly diverse habitats and host plants. "Sebacinales Everywhere" is the title of a report published by a group of researchers from the Institute for Evolution and Oecology in the Department of Organismal Botany at the University of Tübingen in cooperation with colleagues from Switzerland and France. Dr. Michael Weiß from the Department of Organismal Botany is lead author of this paper, which has recently been published in the online journal "PLoS ONE". The researchers studied 128 root samples from 27 families of different plants from four continents. Together with colleagues from the University of Basel (Switzerland) and the University of La Réunion (France), the researchers identified genetic material of Sebacinales fungi in all the plant families investigated. The researchers even detected these fungi in herbarium specimens originating from expeditions to North Africa in the 1830s and 1840s.

The researchers used electron microscope and DNA methods to analyse fern, moss, wheat and maize and discovered that Sebacinales were present in all samples, including the roots of wild Arabidopsis thaliana plants. Arabidopsis thaliana, which is the most popular plant model used by plant geneticists, has not previously been suspected of living in symbiosis with root fungi. The fungi are universally distributed, and no geographical or host patterns were detected. "Our investigation shows that endophytic Sebacinales are not rare, they are actually quite ubiquitous. They may potentially be a previously unrecognised universal hidden force in plant oecosystems," said Weiß suggesting that the multitude of mycorrhizal interactions in Sebacinales may have arisen from an ancestral endophytic habit by specialisation.

Weiß and his colleagues see their findings as a fascinating starting point for investigating symbiotic communities of plants and fungi as well as for application in applied research: "Given the positive effect that sebacinalean fungi had on growth, yield and resistance to abiotic stress and to the fungal pathogens of their plant hosts in experiments under controlled conditions, these results highlight the feasibility of applying Sebacinales as biological fertilisers and biocontrol agents for arable crops in the future."

Further information:

PD Dr. Michael Weiß
University of Tübingen
Faculty of Mathematics and Natural Sciences
Institute for Evolution and Oecology, Organismal Botany
Auf der Morgenstelle 1
D-72076 Tübingen
Tel.: +49 (0)7071 29-72610
E-mail: michael.weiss[at]uni-tuebingen.de

Literature:
Michael Weiß, Zuzana Sýkorová, Sigisfredo Garnica, Kai Riess, Florent Martos, Cornelia Krause, Franz Oberwinkler, Robert Bauer und Dirk Redecker: Sebacinales Everywhere: Previously Overlooked Ubiquitous Fungal Endophytes. PLoS ONE 6(2): e16793. doi:10.1371/journal.pone.0016793

Website address: https://www.biooekonomie-bw.de/en/articles/pm/sebacinales-everywhere-fungi-that-live-in-special-symbioses