Rhizobacteria-Mediated Reprogramming of Phytohormone Landscapes for Mitigating Salinity Stress in Plants

Salinity stress is one of the major stressors that limits yield potential in field crops. Salinity-led imbalances in ionic and water potential, as well as oxidative damage, impair photosynthesis. Plant-growth-promoting rhizobacteria (PGPRs) have been demonstrated to mitigate salinity-stress-induced damage through various mechanisms such as biofilm and exopolysaccharide production, modulation of plant root architecture or molecular signaling involving modulation of sodium/potassium efflux transporters. PGPRs are known to induce biosynthesis and signaling of various phytohormones in plants. PGPR-derived phytohormones can in turn regulate molecular signaling involved in maintaining ion fluxes, preventing salinity-induced senescence, and reinforcing plant root architecture, thereby maintaining plant growth and development under saline conditions. In this review, we provide comprehensive advances on how PGPRs modulate and integrate biosynthesis and/or signaling of various phytohormones, such as auxins, cytokinins, gibberellin, ethylene, abscisic acid, salicylic acid, jasmonates, brassinosteroids and strigolactones, to reshape plant architecture, physiological and biochemical responses in plants under salinity. We integrate molecular evidence with morpho-physiological studies and propose a phytohormone-centric framework to select strains that optimize growth, ion homeostasis and plant stress resilience under salinity.