Signaling cascade during host plant-growth-promoting rhizobacteria interaction in alleviating biotic stress

Abstract

Plants face multifaceted interactions that involve different types of environmental factors. These environmental effects cause several biotic and abiotic stresses that induce disturbance in plant metabolism and their physiologies. Plants have developed specific mechanisms to adapt and survive in stressful environment. Intensive farming and sustainable agriculture demand higher crop productivity equipped with stress resistance. This involves use of soil microorganisms that enhance nutrient uptake and provide resistance against many pathogens. Plant-growth-promoting rhizobacteria (PGPR) and biocontrol agents are the main microbes found in this microbial community. So far, the beneficial effects achieved are related to microbial siderophores, antibiotics, biosynthesis of surfactants and phytohormones, nutrient and spatial competition, mycoparasitism, induced systemic resistance, phage therapy, quorum quenching, and construction of transgenic lines. Phytohormones are organic substances synthesized inside the plants which regulates plant growth and yield and plays its part in inducing tolerance to plants against various environmental stresses both biotic and abiotic. The signaling cascades of hormones generally overlap at times which have an immense impact on plant development and response of plant to stresses. The hormone signal cascade mostly includes an activated secondary messenger or through a series of phosphorylation and dephosphorylation reaction. On response to stimuli (stress), the activated messenger helps in regulating gene expression which in turn affects the levels of hormones and its site of action, which in turn affects the plant growth. PGPR in association with roots of higher plants increase or decrease the phytohormones level, showing a new type of hormonal interaction. Based on the stage of plant growth and type of cell, the levels of various hormones vary, which indirectly determines the response of plants to different biotic and abiotic stresses present at specific plant growth stage. This review compiles the hormonal crosstalk in plants involved in plant development. The interaction between phytohormones under abiotic and biotic stresses will be elucidated. miRNA-based regulation along with stress responsive cis elements during hormonal responses will be elaborately reviewed. Finally, the impact of PGPR will be elucidated under various biotic stresses from the point of view of phytohormone synthesis and its physiological interaction. PGPR provides cross-protective properties through improvement in defense mechanism controlling pathogen resistance through induced systemic resistance and alleviating abiotic stress through influencing the phytohormones metabolism. PGPR multiplying under stress condition induces tolerance in plant by altering the hormone synthesis and their response pattern. Gene expression and phytohormone production is regulated by bacteria crosstalk via quorum sensing. Further studies are required to understand the interaction of rhizosphere microbes and plant system with respect to effect on phytohormone. © 2024 Elsevier Inc. All rights reserved.