Amelioration of Salt Stress Tolerance in Plants by Plant Growth-Promoting Rhizobacteria: Insights from “Omics” Approaches

Abstract

Soil salinity is one of the major abiotic stresses known to drastically reduce agricultural productivity. Prolonged salinity stress in glycophytic plants may cause oxidative damage to the cells, thereby causing cell death. Although salt-tolerant crops can be produced by genetic engineering by introducing novel transgenes or by altering the expression levels of the existing genes, substantial enhancement of crop productivity is questionable, and the introduction of genetically modified transgenic plants into the ecosystem is not well received. Breeding for environmental stress tolerance in plants is also challenging, time consuming and cost intensive. Alternative to the above mentioned, the identification and usage of beneficial rhizobacteria are efficient, cost-effective approaches that have been successfully employed in various crops to improve their growth, yield and tolerance to salt stress. These beneficial plant growth-promoting rhizobacteria are naturally occurring soil bacteria that rapidly colonize plant roots and benefit plants by various mechanisms. These bacteria are able to survive in high-salt concentrations of the soil due to their inherent capability to accumulate some of the important compatible osmolytes required for maintaining intracellular osmotic homeostasis or possess the transporters that help them survive under high-salt conditions among other adaptive mechanisms. These soil bacteria grow luxuriously under high-salt conditions and possess plant growth-promoting and protecting traits that are responsible for facilitating plant growth and survival under high-salt conditions in the soil. In this chapter, we summarize the salinity stress responses in plants in terms of physiological, biochemical and molecular mechanisms followed by the plant growth-promoting rhizobacteria-mediated stress amelioration phenomenon. We describe the role of ‘omics’ approaches in generating comprehensive information essential for better understanding of plant growth promotion by plant growth-promoting rhizobacteria.