08/30/2024
Newly discovered abilities of a well-known laboratory fungus
The great diversity of fungi is often considered in plant research primarily because of their potential as plant pests. However, the range of interactions between fungi and plants is much wider, ranging from harmful interactions to mutually beneficial relationships.
In particular, the extensive group of endophytic fungi, which live inside plants and maintain harmful, neutral or symbiotic relationships with the host, have only been researched to a limited extent. The Department of Botanical Genetics and Molecular Biology, headed by Professor Frank Kempken at Kiel University, is investigating the molecular basis of such fungus-plant interactions.
In a new study, Kiel researchers have analysed the filamentous fungus Neurospora crassa with regard to its possible interactions with various plant species. Little is known about the ecology and natural lifestyle of the fungus, which is used worldwide as a genetic and molecular biological model organism.
Thanks to a combination of colonisation experiments and various imaging methods, the Kiel scientists discovered that the fungus can colonise the grain-like grass species Brachypodium distachyon permanently and stably without damaging the host organism.
They were thus able to demonstrate a presumably favourable and stable relationship between the fungus and a plant that might also occur naturally. Both species, the fungus and the grass, have already been studied in detail in terms of their genetic and molecular properties. Together, they are suited as a novel model system for investigating fungus-plant interactions. The researchers from the Botanical Institute at Kiel University, who are also active in the Kiel Plant Center (KPC), recently published their results in the Journal of Fungi.
Endophytic occurrence in grasses detected experimentally for the first time
Little is known about the natural occurrence of N. crassa to date. "It is assumed that the fungus colonizes dead sugar cane, for example, where it degrades plant material. An American research team also found evidence of an association between the fungus and a certain type of pine tree," explains Dr Krisztina Kolláth-Leiß, a research associate in Kempken's team.
In order to find out more about the ecological role of the fungus, the Kiel research team carried out a series of colonisation experiments. They applied fungal spores to the roots of pre-grown plants of various species and observed over the course of around a week whether and how the fungus colonised the tissue and what influence it had on plant growth. Initially, the colonisation experiments were unsuccessful; for example, fungus and plant did not show any stable interactions in maize and the classic model plant Arabidopsis thaliana.
"We then repeated our experiments with the grass species Brachypodium distachyon, whose family also includes wheat, rye and barley, for example. Here, N. crassa was found to grow extensively around the plant root, while the shoot of the grass did not appear to be affected and the plant grew normally overall," says Kolláth-Leiß. The extensive growth on the roots provides the first evidence of an endophytic interaction between this fungus species and a plant root and suggests that this interaction can also occur in nature. Their co-existence in common habitats and the already known presence of closely related fungal species on the roots of the grass also support this theory, according to the botanist.
Using various imaging methods, including electron and confocal microscopy, contributed to the study by Kiel University's Central Microscopy (ZM) facility, the research team observed how the fungal colonisation of the Brachypodium roots took place in detail. "We were able to show, for example, that the fungus was able to spread via the plasmodesmata, i.e. internally from plant cell to plant cell. This also indicates an endophytic relationship between fungus and plant," emphasises Kolláth-Leiß.
Overall, a stable interaction between N. crassa and B. distachyon was established in the experiments, which mainly manifested itself in a very dense fungal colonisation of the plant roots. The researchers hypothesise that this could possibly help the plant to absorb water. Such an interaction would be beneficial for both sides, as it increases the competitiveness of the plant and at the same time improves the nutrient supply of the fungus.
Novel model system for the investigation of fungus-plant interactions
"Multicellular host organisms in general and thus also plant tissues offer suitable niches for the colonisation of microorganisms, which can lead to various, but often very specific forms of interactions. Our new results indicate that fungi have a much broader ability to interact endophytically with host plants than previously thought," emphasises Kempken, KPC member and head of the Department of Botanical Genetics and Molecular Biology at Kiel University.
The study thus provides a basis for studying the range of fungus-plant interactions and their dependence on changing environmental conditions using the novel model system of the endophytic relationship between N. crassa and B. distachyon. "Such interactions play an important role in plant health. However, it has not yet been sufficiently clarified how endophytic relationships between fungi and plants can change from beneficial to harmful in the course of altered environmental conditions.
In further studies, we want to use this model to understand which factors stabilise or destabilise these interactions at the molecular level. Such findings could be used in plant breeding in the future, for example, to counteract the effects of changing growth conditions in the course of climate change in a targeted manner," Kempken looks ahead.
Source: University of Kiel