Root exudates, the warrior of plant life: Revolution below the ground

Plants are sessile organisms that are constantly dealing with different abiotic and biotic stresses such as salinity, drought, chilling, high temperature, flooding; pathogen or pest infections which can severely affect their growth and productivity. To cope up with these stressful conditions, plants have developed a complex network of adaptive mechanisms among which the production of root exudates is a key mechanism. Exudates that are secreted through the plant roots are complex mixtures of organic compounds (primary, secondary metabolites, ions and enzymes, etc.). The process of secretion of root exudates through the plasma membrane of root cells and the transporters involved have been studied in detail. In recent years many findings have also shown the protective potential of root exudates in enhancing plant tolerance to abiotic stresses and resistance against biotic stresses. Root exudates can modulate the physical and chemical properties of soil, regulate water and nutrient availability, and interact with microorganisms to enhance plant stress tolerance. In this review, we summarize the recent advances in understanding the interaction between plants and the soil environment mediated by root exudates. This article also highlights the changes induced in the metabolic profiles of plants leading to an altered exudation process under stress conditions to protect the plants. The mechanisms underlying the safeguarding effect of root exudates during stresses are also discussed and evaluated. Understanding these mechanisms can provide new opportunities to develop new crop varieties that are more resilient to different stress factors and can contribute to global food security.