Roles of the Plant Immune Response in Root Nodule Symbiosis

The symbiotic relationship between legume plants and soil bacteria has been an important focus of research for several decades because of its agricultural and environmental potential to create a variety of nitrogen-fixating plants capable of fertilizing the soil and producing crops with high protein content. The symbiosis is largely plant-controlled, with the plant’s innate immune responses playing an important role in initiating and regulating the symbiosis. This review elucidates the role of plant immune responses in forming symbiosis with microorganisms, including how molecular cues between host and symbiont suppress the plant defense pathways, as well as how the plant can dominate the symbiosis through defense-like reactions at key signaling steps in the symbiosis. Understanding the mechanisms of regulated defense responses during nitrogen-fixing symbiosis may help us transfer this ability into non-legume plants, creating crops with higher nutrient yields and promoting sustainable and environmentally-friendly agricultural practices.