Secrets of cooperation between trees and fungi revealed

Trees and fungi have constructed a close relationship with the passing of the ages. Fungi like to grow between the roots of trees and the arrangement is beneficial to both partners. Their delicate balance is now being revealed for the very first time. VIB researchers at Ghent University in colaboration with an international team have succeeded in unravelling the genetic code of the Laccaria bicolor fungus. This new information is crucial to our knowledge. It will lead to a better understanding of how fungi help trees to grow and how together they can be indicators of climate change.

Trees and fungi live happily together

Trees are the lungs of the earth. They draw CO₂ from the atmosphere and convert it into sugars, which then become a source of energy. In the process they breathe O₂ back into the atmosphere. This “green” production of biomass – trees account for 90% of the planet’s land-based biomass – is a major influence on the health of our planet.

Trees grow better and faster when certain specialized micro-organisms occur in their root systems. One such organism is the Laccaria bicolor fungus. The symbiotic relationship of the fungus and the tree root systems is advantageous to both. The fungus facilitates the uptake of scarce nutrients such as phosphates and nitrogen and protects the roots against parasites in the soil. In return they are able to draw on the sugars in the roots. 85% of all plants and trees are dependent on symbiotic processes of this kind for their growth.

Genetic code of symbiotic fungus yields up first secrets

An international collaborative project was set up to characterize the genome of the soil fungus Laccaria bicolor . VIB scientists Pierre Rouzé and Yves Van de Peer, working with France’s renowned INRA and JGI of the US, have sequenced the DNA of the fungus. They have been able to identify 20,000 genes in the fungal genome. Their analyses immediately resulted in new knowledge, including the discovery of an arsenal of small proteins known as SSPs (small secreted proteins), which are only made at those places where the fungus and the tree root come into contact. The genome study also revealed that the fungus is unable to break down plant cells but does affect the cell walls of pathogens. This could explain how these fungi protect their symbiotic partners. Additionally the researchers identified genes which play a role in communicating with all the players in the surroundings of the roots of the host tree during growth.

Fungi: barometers of climate change?

A better understanding of the genetic secrets of this fungus does not just hold out the prospect of being able to optimize biomass production; research into the delicate balance between fungus and tree may also yield important information that could be used to monitor climate change. Not only has the genome of the Laccaria bicolor been fully sequenced, that of the poplar, one of the trees with which it forms a relationship, is also fully known. This will make it possible to find out exactly how tree and fungus cooperate and react to stress factors such as drought or extreme temperatures resulting from climate change. The hope exists that the assembled information will result in concrete applications in which trees and fungi can be deployed to the benefit of both people and the environment.

Source : VIB (the Flanders Institute for Biotechnology)