Opening the gate: how a fungus finds its way into a tree root

What is it about?

Tree roots can enter into a beneficial interaction with soil fungi called ectomycorrhiza. This requires that root cells loosen, and the pectin connecting those cells is broken down to accommodate fungal hyphae in between root cells in a structure that allows nutrient transfer between the two partners. Here we describe how the fungus Laccaria bicolor contributes to the loosening of neighbouring root cells by excreting an enzyme that catalyzes the first step towards pectin breakdown.

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Photo by Kevin Young on Unsplash

Photo by Kevin Young on Unsplash

Why is it important?

Understanding the mechanisms of how trees and fungi engage into and maintain a mutually beneficial relationship can help us design strategies to choose tree and fungal partners that can interact with each other. This is why it is important to better understand how the symbiosis is established, and further how the nutrient exchange between both partners is regulated and influenced by environmental conditions. Our research addresses the first aspect. Fungal genome analyses over the past decade have allowed us to understand that many of the ectomycorrhizal fungi have lost their repertoire of plant cell wall degrading enzymes when they evolved from a saprophytic lifestyle (acquiring carbon from degradation of dead matter) to a symbiotic lifestyle (using carbon provided by living plants through photosynthesis). Here we contribute to the understanding that a core set of pectin modifying genes in the model fungus Laccaria bicolor have been retained and contribute to the establishment of the symbiosis. It had been known for many years that pectin degradation indeed is a part of the symbiosis establishment but until very recently it wasn't known whether the fungus contributes to this process or it's solely based on plant enzymes. Now we know that the fungus has an important role in this process.

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