Recent Insights on Biological and Ecological Aspects of Ectomycorrhizal Fungi and Their Interactions

Abstract

The roots of most terrestrial plants are colonized by mycorrhizal fungi. They play a key role in terrestrial environments influencing soil structure and ecosystem functionality. Around them a peculiar region, the mycorrhizosphere, develops. This is a very dynamic environment where plants, soil and microorganisms interact. Interest in this fascinating environment has increased over the years. For a long period the knowledge of the microbial populations in the rhizosphere has been limited, because they have always been studied by traditional culture-based techniques. These methods, which only allow the study of cultured microorganisms, do not allow the characterization of most organisms existing in nature. The introduction in the last few years of methodologies that are independent of culture techniques has bypassed this limitation. This together with the development of high-throughput molecular tools has given new insights into the biology, evolution, and biodiversity of mycorrhizal associations, as well as, the molecular dialog between plants and fungi. The genomes of many mycorrhizal fungal species have been sequenced so far allowing to better understanding the lifestyle of these fungi, their sexual reproduction modalities and metabolic functions. The possibility to detect the mycelium and the mycorrhizae of heterothallic fungi has also allowed to follow the spatial and temporal distributional patterns of strains of different mating types. On the other hand, the availability of the genome sequencing from several mycorrhizal fungi with a different lifestyle, or belonging to different groups, allowed to verify the common feature of the mycorrhizal symbiosis as well as the differences on how different mycorrhizal species interact and dialog with the plant. Here, we will consider the aspects described before, mainly focusing on ectomycorrhizal fungi and their interactions with plants and other soil microorganisms.

Defense Enzymes in Mycorrhizal Tomato Plants Exposed to Combined Drought and Heat Stresses

“…In the present study, we attempted to mimic the field condition of a relatively long-lasting drought period together with a short period of heat stress (heat shock), which usually takes place at mid-day (combined drought and heat shock), and the combination of a drought period with more prolonged heat stress, which is a regular occurrence in semi-arid and hot growing regions. Arbuscular mycorrhizal fungi establish mutualistic interactions with more than 80% of all plant species, providing a direct physical link between the soil and plant roots [20,40,41]. AMF is one of the most used biological agents in boosting plant growth, helping in photosynthesis, and enhancing tolerance to biotic and abiotic stresses [42,43].…”

“…Hence, the plant has an antioxidant defense system to prevent oxidative stress consisting of several antioxidant enzymes such as superoxide dismutase (SOD); ascorbate peroxidase (APX); catalase (CAT) and glutathione reductase (GR); and non-enzymatic antioxidants like ascorbic acid, reduced glutathione (GSH), and tocopherol to scavenge excessive ROS [17,18]. Arbuscular mycorrhizal fungi (AMF) belonging to Phylum Glomeromycota are one of the most important microorganisms that form a symbiotic relationship with more than 80% of land plants [19,20]. Several studies have shown that AMF can enhance the growth of the host plant through improving soil structure, nutrient, and water uptake [7,21,22].…”

An ectomycorrhizal fungus alters sensitivity to jasmonate, salicylate, gibberellin, and ethylene in host roots

“…The formation of ECM involves complex developmental reprogramming of host tree morphology, including enhanced LR initiation (Rincón, Priha, Sotta, Bonnet, & Le, ; Tranvan, Habricot, Jeannette, Gay, & Sotta, ), root hair decay (Horan et al, ; Béguiristain and Lapeyrie, ), and elongation of epidermal and cortical cells (Horan et al, ; Kottke & Oberwinkler, ). Apoplastic hyphal penetration is accompanied by changes in plant and fungal cell wall composition (Mello & Balestrini, , and references therein). These changes result in the aggregation of fungal hyphae and their adhesion to the plant cell wall (Laurent et al, ; Tagu et al, ; Tagu & Martin, ), hemicellulose and pectin degradation (Sillo et al, ; Veneault‐Fourrey et al, ), and plant cell wall expansion and de novo biogenesis (Luo et al, ; Sebastiana et al, ; Veneault‐Fourrey et al, ).…”

“…The formation of ECM involves complex developmental reprogramming of host tree morphology, including enhanced LR initiation (Rincón, Priha, Sotta, Bonnet, & Le, 2003;Tranvan, Habricot, Jeannette, Gay, & Sotta, 2000), root hair decay (Horan et al, 1988;Béguiristain and Lapeyrie, 1997), and elongation of epidermal and cortical cells (Horan et al, 1988;Kottke & Oberwinkler, 1987). Apoplastic hyphal penetration is accompanied by changes in plant and fungal cell wall composition (Mello & Balestrini, 2018, and references therein).…”

Structural plasticity in root-fungal symbioses: diverse interactions lead to improved plant fitness

“…ECM hosts are mostly woody species belonging to Betulaceae , Fagaceae , Dipterocarpaceae , Myrtaceae , Pinaceae , Salicaceae , Cupressaceae , Rosaceae , Fabaceae , Aceraceae , Euphorbiaceae , and Ulmaceae , whilst there are up to 20,000 basidiomycetous, ascomycetous and Mucoromycotina fungi involved in this symbiosis ( Rinaldi, Comandini & Kuyper, 2008 ; Tedersoo, May & Smith, 2010 ). Climatic factors have been suggested as the main drivers of ECM diversity and distribution globally, and the species richness of ECM fungi peak at mid-latitudes, especially in temperate forests and Mediterranean biomes of the Northern Hemisphere i.e., where pine forests are the dominant vegetation ( Tedersoo et al, 2014 ; Mello & Balestrini, 2018 ). Environmental and host factors have been shown to drive ECM diversity across the European forests ( Van der Linde et al, 2018 ).…”