Abstract
Microbes living on the root surface and the inner plant tissues such as rhizobacteria, arbuscular mycorrhizal fungi, endophytic bacteria, and rhizobia mutually cooperate with each other and induce a beneficial effect on plant growth. They colonize the root system and play an important role in stimulation of plant growth, stress tolerance, and nutrient acquisition of plants by altering the root system and altering physiological processes of plants. PGPR-rhizobia-AMF tripartite symbiosis improves plant growth under stress through induction of osmoregulation, hormonal balance, increase in nutrient acquisition, improving physiochemical activity, compositions, tissue water content, and alters metabolic interactions among the partners. These are coordinately involved in the adaptation of plants to abiotic stress through several mechanisms which include production of phytohormones, ACC deaminase enzyme, and mitigation of oxidative damage by improving enzymatic and nonenzymatic antioxidant defense system, modulation of phytohormones, and induction of acquired systemic tolerance. Mutualistic relationship of microbial symbionts could be an approach to increase plant stress tolerance to various abiotic stress factors.