Induction of regulatory mechanisms by plant growth promoting rhizobacteria in crops facing drought stress

Climate change and global warming are leading to severe drought stress, causing damage to crops in different regions of the world. Drought stress is an abiotic stress that interferes with major metabolic pathways, influencing mainly morphological, physiological and biochemical parameters of plants, ultimately resulting in decreased growth and yield of crops. Plants should be able to utilise available moisture efficiently, and there is a need to focus on organic and eco-friendly methods for improving crops facing drought stress. A practical approach for enhancing growth and development under stressful conditions is the application of plant growth promoting rhizobacteria (PGPR), soil microbes that help plants to cope with extreme ecological conditions. This review aims to highlight the function of various PGPR metabolites that help to mitigate water-deficit conditions. These microbes exist naturally in the rhizosphere of plants, and they enhance plant growth by several direct mechanisms such as aminocyclopropane-1-carboxylate deaminase and osmolyte production, secretion of exopolysaccharides and phytohormones, triggering of antioxidant defence mechanisms against reactive oxygen species and production of volatile organic compounds, as well as by indirect mechanisms including enhancing induced systemic resistance and pathogen suppression. This review recommends the use of PGPR for improving growth and development of crops under drought stress and supports their role as effective and sustainable bioinoculants for enhancing the growth and production of crops.