Plant survival under drought stress: Implications, adaptive responses, and integrated rhizosphere management strategy for stress mitigation

In many regions of the world, the incidence and extent of drought spells are predicted to increase which will create considerable pressure on global agricultural yields. Most likely among all the abiotic stresses, drought has the strongest effect on soil biota and plants along with complex environmental effects on other ecological systems. Plants being sessile appears the least resilient where drought creates osmotic stress, limits nutrient mobility due to soil heterogeneity, and reduces nutrient access to plant roots. Drought tolerance is a complex quantitative trait controlled by many genes and is one of the difficult traits to study and characterize. Nevertheless, existing studies on drought have indicated the mechanisms of drought resistance in plants on the morphological, physiological, and molecular basis and strategies have been devised to cope with the drought stress such as mass screening, breeding, marker-assisted selection, exogenous application of hormones or osmoprotectants and or engineering for drought resistance. These strategies have largely ignored the role of the rhizosphere in the plant's drought response. Studies have shown that soil microbes have a substantial role in modulation of plant response towards biotic and abiotic stress including drought. This response is complex and involves alteration in host root system architecture through hormones, osmoregulation, signaling through reactive oxygen species (ROS), induction of systemic tolerance (IST), production of large chain extracellular polysaccharides (EPS), and transcriptional regulation of host stress response genes.