Research progress on the mechanism of AM fungi for improving plant stress resistance

Arbuscular mycorrhizae (AM) fungi could increase plant resistance to biotic and abiotic stresses.AM fungi could improve plant resistance to abiotic stresses, including drought, high or low temperature, heavy metal, and salt. The mechanism includes improving plant nutrient absorption, the accumulation of osmotic adjustment substances and activities of antioxidative enzymes, strengthening the effects of osmotic adjustment and maintaining the balance of plant hormones, and increasing auxin synthesis, and regulating carbon and nitrogen metabolism. AM fungi could also induce plant defense gene expression and enhance the capacity of plant roots and mycelium to hold heavy metal. The mechanism of AM fungi for defense against plant disease and insects may include building the mycelium network that can form mechanical barriers for the pathogen that is invading, enhancing the activities of resistance-related enzymes, synthesizing secondary metabolites associated with disease and insect resistance, promoting the expression of genes related to diseases and pests, and transmission by mycelium of the signal of insect resistance defense to improve the insect resistance of adjacent plants. We summarize the effects of AM fungi on plant stress resistance and the mechanisms found both at home and abroad in recent years.