Plant Immunity Modulation in Arbuscular Mycorrhizal Symbiosis and Its Impact on Pathogens and Pests

Arbuscular mycorrhizal (AM) symbiosis is the oldest and most widespreadmutualistic association on Earth and involves plants and soil fungi belongingto Glomeromycotina. A complex molecular, cellular, and genetic develop-mental program enables partner recognition,fungal accommodation in planttissues, and activation of symbiotic functions such as transfer of phospho-rus in exchange for carbohydrates and lipids. AM fungi, as ancient obligatebiotrophs, have evolved strategies to circumvent plant defense responses toguarantee an intimate and long-lasting mutualism. They are among thoseroot-associated microorganisms able to boost plants' ability to cope withbiotic stresses leading to mycorrhiza-induced resistance (MIR), which canbe effective across diverse hosts and against different attackers. Here, weexamine the molecular mechanisms underlying the modulation of plant im-munity during colonization by AM fungi and at the onset and display of MIRagainst belowground and aboveground pests and pathogens. Understandingthe MIR efficiency spectrum and its regulation is of great importance to op-timizing the biotechnological application of these beneficial microbes forsustainable crop protection.