Edible Ectomycorrhizal Mushroom Molecular Response to Heavy Metals

Heavy metal pollution poses a significant threat to the environment, public, and soil health. Ectomycorrhizal fungi are thought to enhance mineral nutrition of their host plants and to confer increased tolerance toward toxic metals. The responses of mycorrhizal fungi to toxic metal cations are diverse and may consist of a reduced uptake of metals by extracellular or intracellular chelation or increased efflux out of the cell or into sequestering compartments. Rhizosphere chemistry is critical to understanding the interactions of mycorrhizae with polluted soils. This, linked to the fact that mycorrhizal diversity is normally high, even on highly contaminated sites, suggests that this diversity may have a significant role in colonization of contaminated sites by ectomycorrhizal fungi. However, the molecular mechanisms underlying the response of ectomycorrhizal fungi to heavy metals in general remain poorly understood, although the recent Tuber melanosporum Vittad. genome sequencing and transcriptome analyses have obtained a global view of metal homeostasis-related genes and pathways in this fungus. The focus of this review is to describe and discuss the tolerance of the ectomycorrhizal fungi, in particular the edible ones, under heavy metal stress conditions.