Microbial Inoculants in Amelioration of Stress by Regulation of Signalling Cascades in Plant

In agriculture, rapid manipulation and exploitation of PGPR (plant growth-promoting rhizobacteria) is rising rapidly due to vast functionality of plant-protective and growth-related benefits in plants against biotic and abiotic stresses. The interaction between host plants and the microbial community in the rhizospheric zone is a very complex and dynamic process which regulates the effective communication system in a coordinated manner. This interaction might happened at multiple levels, i.e., either intraspecies, interspecies, or tritrophic interaction. PGPR-assisted plant growth outcome and stress reduction outcome are triggered by means of the signal transduction pathway during plant–microbe interaction. Rapid advancement in technology has opened a new dimension for exploring the functionality of specific signal molecules and related chemical cues which participate in the communication process as well as induction of defense mechanism. The precise and comprehensive gene expression mechanism and communication between plant and microbes could provide enough strength to understand the mechanism behind activation of plant’s immune response. The activation of plant PRR and NLR by microbial effector proteins activates the MAPK and CDPK pathways through transphosphorylation. These signalling pathways play a vital role as regulators of gene expression, influencing various functions such as plant immunity, virulence properties, and plant–microbe communications. Over the past decades, the use of PGPR has emerged as a promising tactic to improve tolerance to abiotic and biotic stresses in host plants. Therefore, it is imperative to understand the mechanism overview of the microbe–plant interaction phenomenon and understand its importance. This chapter focuses on elucidating the effects of defense signalling on the root microbiome. It also explains the signalling molecules produced by both microbes and plants, which contribute to the defense mechanisms and tolerance responses of host plants against biotic and abiotic stresses.