Plant-Mycorrhizal and Plant-Rhizobial Interfaces: Underlying Mechanisms and Their Roles in Sustainable Agroecosystems

Rhizospheric plant-microbe symbiotic interactions involve numerous microbial populations which have a significant impact on plant growth and productivity. Abiotic stresses are serious threats to agriculture and negatively affect the soil-microbe-plant continuum, which is also responsible for reduced yield. Rhizospheric microbes, especially arbuscular mycorrhizal fungi (AMF) and rhizobia (Rh), are potential economical and eco-friendly resources for counteracting abiotic stresses in plants. These microbial interactions involve the release of signaling molecules, such as Myc factors by AMF and Nod factors by Rh, which initiate communication between these microbes and plants leading to colonization, nodulation, and arbuscule formation. Both these microbes are relatively tolerant to extreme adverse conditions and can improve growth and productivity of stressed plants by improving soil and root system architecture (RSA), nutrient uptake, ion homeostasis, sequestration, and compartmentalization, reducing osmotic and oxidative stress, etc. Moreover, both these symbionts act synergistically and provide various beneficial effects in stressed plants. However, there are a number of gaps in understanding the various steps involved in the establishment of symbioses, the signaling molecules, nutrient exchange through the symbiotic interface and genes involved, as well as the modes of action/mechanism of the AMF and Rh in imparting abiotic stress resistance in plants. This chapter bridges the gap and summarizes the mechanisms adopted by AMF and Rh in imparting stress resistance and enhancing crop productivity for a sustainable agroecosystem.