Arbuscular mycorrhizas: The lives of beneficial fungi and their plant hosts

Abstract

When plants colonized the land 450 million years ago, they were already associated to soil fungi, which assisted them in facilitating the uptake of mineral nutrients. This symbiotic association is known as mycorrhiza, a word that covers all the symbioses established between plants and beneficial fungi. Their presence in most environments suggests that evolution has promoted mycorrhizas because of the benefits gained by both partners. The improved nutrient status has a positive impact on the overall plant physiology, as it influences growth, water absorption and protection from root diseases. Mycorrhizal fungi instead acquire organic carbon directly from their green hosts, and accomplish their life cycle. These features are considered as landmarks of mutualistic symbioses. Owing to the huge diversity of plant and fungal taxa involved, and the multiplicity of the resulting interactions, mycorrhizas are usually classified in two broad categories, known as ecto- and endomycorrhizas, depending on whether the fungus colonizes the root’s intercellular spaces or develops inside the plant cells. The aim of this chapter is to focus on arbuscular endomycorrhizal symbiosis, which is the most ancient and common plant-fungal association, and to provide an overview that updates traditional knowledge with recent data.