Plant Growth-Promoting Microbial-Mediated Induced Systemic Resistance in Plants: Induction, Mechanism, and Expression

In the agroecosystem, plants are an attractive source of nutrients and life environment for many microbes. Pathogenic as well as nonpathogenic microbes get colonized to the plants resulting in various diseases and beneficial effects on plant growth or stress resistance, respectively. Plants are generally resistant to the majority of phytopathogens due to the presence of an efficient and complex immune system which is able to deal with most microbial invaders ubiquitously present in the environment. Plant growth-promoting microbes (PGPMs) elicit a higher level of resistance in addition to an indigenous immune system in the form of induced systemic resistance in plants and provide a heightened level of protection. Induced systemic resistance is a pre-activated induced resistance in plants leading to defense-related protein activation which is independent of salicylic acid and dependent on jasmonic acid and ethylene. Nonexpressor of pathogenesis-related protein 1 (NPR1) works as a master regulator of hormonal defense signaling pathway leading to activation of pathogenesis-related and defense-related protein that depends on the preceding signals. This chapter focuses on recent research study concerning interaction between PGPMs and plants under biotic stress condition.