Articulating beneficial rhizobacteria-mediated plant defenses through induced systemic resistance: A review

Induced systemic resistance (ISR) is a mechanism by which certain plant beneficial rhizobacteria and fungi produce immunity, which can stimulate crop growth and resilience against various phytopathogens, insects, and parasites. These beneficial rhizobacteria and fungi improve plant performance by regulating hormone signaling, including salicylic acid (SA), jasmonic acid (JA), prosystemin, pathogenesis-related gene 1, and ethylene (ET) pathways, which activate the gene expression of ISR, the synthesis of secondary metabolites, various enzymes, and volatile compounds that ultimately induce defense mechanisms in plant. To protect themselves from disease, plants have various advanced defense mechanisms in which local acquired resistance, systemic gene silencing, systemic wound response, systemic acquired resistance (SAR), and ISR are involved. Several rhizobacteria activate the SA-dependent SAR pathway by producing SA at the root's surface. In contrast, other rhizobacteria can activate different signaling pathways independent of SA (SA-independent ISR pathways) such as those dependent on JA and ET signaling. The main objective of this review is to provide insight into the types of induced resistance utilized for plant defense. Further to this, the genetic approaches used to suppress disease-causing genes, i.e., RNA interference and antisense RNA, which are still underutilized in sustainable agriculture, along with the current vision for virus-induced gene silencing are also discussed.