Arbuscular mycorrhizal fungi-induced tolerance to chromium stress in plants

Chromium (Cr) is one of the toxic elements that harms all forms of life, including plants. Industrial discharges and mining largely contribute to Cr release into the soil environment. Excessive Cr pollution in arable land significantly reduces the yield and quality of important agricultural crops. Therefore, remediation of polluted soil is imperative not only for agricultural sustainability but also for food safety. Arbuscular mycorrhizal fungi (AMF) are widespread soil-borne endophytic fungi that form mutualistic relationships with the vast majority of land plants. In mycorrhizal symbiosis, AMF are largely dependent on the host plant-supplied carbohydrates and lipids, in return, AMF aid the host plants in acquiring water and mineral nutrients, especially phosphorus, nitrogen and sulfur from distant soils, and this distinguishing feature of the two-way exchange of resources is a functional requirement for such mutualism and ecosystem services. In addition to supplying nutrients and water to plants, the AMF symbiosis enhances plant resilience to biotic and abiotic stresses including Cr stress. Studies have revealed vital physiological and molecular mechanisms by which AMF alleviate Cr phytotoxicity and aid plants in nutrient acquisition under Cr stress. Notably, plant Cr tolerance is enhanced by both the direct effects of AMF on Cr stabilization and transformation, and the indirect effects of AMF symbiosis on plant nutrient uptake and physiological regulation. In this article, we summarized the research progress on AMF and associated mechanisms of Cr tolerance in plants. In addition, we reviewed the present understanding of AMF-assisted Cr remediation. Since AMF symbiosis can enhance plant resilience to Cr pollution, AMF may have promising prospects in agricultural production, bioremediation, and ecological restoration in Cr-polluted soils.