Epigenetics and the symbiosis between trees and fungi

To share nutrients and enhance their capacity for environmental adaptability, tree roots frequently collaborate with fungi. Although this interaction is mutually beneficial (namely, ectomycorrhizae), the biological mechanisms at play have not yet been completely analyzed.

It has now been proven for the first time by two research teams from the INRAE-University of Lorraine and the Université of Orléans that epigenetics regulates the development of the symbiotic association between the model tree poplar and an ectomycorrhizal fungus.

This is a significant advancement in the comprehension of the processes necessary to create ectomycorrhizal symbiosis, which is crucial for the robust development and functionality of forests and trees. On February 20^th, 2023, the findings were published in the New Phytologist.

Ectomycorrhizae is a symbiosis formed between tree roots and fungi that are present in the soil. The ectomycorrhizal symbiosis is essential for tree nutrition, notably water uptake, and also affects the ability of trees to adapt to their environment.

It is an intrinsic component of temperate and boreal forest ecosystems. Current understanding regarding the formation and modulation of this symbiotic process is still in its infancy and, until recently, the possibilities of epigenetic regulation remained unexplored.

Every cell in the body duplicates the whole sequence of DNA, which contains the genetic information that characterizes every living thing. Yet, a separate mechanism known as epigenetics regulates the gene activity patterns required for each cell type to adapt to its environment and enables the transmission of these patterns from one generation to the next.

Epigenetic control of the symbiosis between trees and fungi

The role of DNA methylation (an epigenetic mark) in the mycorrhization of poplar, a model forest tree, was examined by two teams of researchers from INRAE-University of Lorraine and the University of Orléans, working with scientists from the CEA (The French Alternative Energies and Atomic Energy Commission), and from the Spanish and US institutions.

The team’s research on the epigenetic processes in trees was based on the usage of transgenic poplar lines that already existed and whose regulatory genome DNA methylation status had been altered for research.

They compared the functional responses of the modified poplars to mycorrhizal fungi with those of a wild-type (control) line of the same species that had not undergone any modification.

The findings were conclusive: mycorrhization capacity was decreased (up to 40% in one instance) in lines whose genomic DNA methylation rates had been lowered. These findings imply that DNA methylation plays a key role in a host tree’s ability to establish the symbiotic interactions required for robust growth.

The host’s DNA methylation status also affected the epigenetic regulation of the fungal partner, which occurred in both directions.

This groundbreaking study offers up a new area of research that will further the current understanding of the symbiotic relationship between two living organisms. Future applications for managing forests that are impacted by climate change, such as drought, could potentially benefit from it.