Mycorrhizal fungi volatiles: determining the fate of plants against stress?

Mycorrhizal fungi represent one of the oldest and most successful symbioses in plant evolution. Communication among mycorrhizal fungi and plants occurs prior to direct contact among them through different and variable biochemical signals, including microRNAs, hormones, small peptides and volatile organic and inorganic compounds. Volatile organic compounds (VOCs) emerge as key chemical signals that enable the transmission of chemical messages modulating plant and microorganism responses in both below- and above-ground ecosystems. The diversity and concentration of mycorrhizal VOCs will vary depending on the environment and the emitting organism and are usually related to changes in the conformation of root architecture and lateral root formation mediated by auxin and strigolactones. Moreover, the study of the effects of mycorrhizal VOCs in the tolerance to abiotic and biotic stress are still scarce although there are some promising results pointing out to the effect of these VOCs in plant development under osmotic stress conditions, and their properties as antifungal and antibacterial molecules. However, the information regarding the molecular mechanisms involved in mycorrhizal VOCs signaling and their effect on plants remains still elusive. The understanding of VOC-mediated plant-mycorrhizal interactions, together with the technical improvements for their detection and mode of application in the field, will open new avenues for biotechnological crop improvement and management that not only will reduce the dependence on agrochemicals but also fosters soil health and plant resilience.