Induced Systemic Resistance for Improving Plant Immunity by Beneficial Microbes

Abstract

Plant beneficial microorganisms improve the health and growth of the associated plants. Application of beneficial microbes triggers an enhanced resistance state, also termed as induced systemic resistance (ISR), in the host, against a broad range of pathogens. Upon the activation of ISR, plants employ long-distance systemic signaling to provide protection for distal tissue, inducing rapid and strong immune responses against pathogens invasions. The transmission of ISR signaling was commonly regarded to be a jasmonic acid- and ethylene-dependent, but salicylic acid-independent, transmission. However, in the last decade, the involvement of both salicylic acid and jasmonic acid/ethylene signaling pathways and the regulatory roles of small RNA in ISR has been updated. In this review, the plant early recognition, responsive reactions, and the related signaling transduction during the process of the plant–beneficial microbe interaction was discussed, with reflection on the crucial regulatory role of small RNAs in the beneficial microbe-mediated ISR.

Biological Control of Plant Pathogens: A Global Perspective

“…Plant defense against biotic threats is known to be activated by beneficial microorganisms [ 80 ], through a variety of mechanisms, giving plants resistance to diseases [ 139 ]. However, the molecular processes through which plants with an activated defense respond to biotic stresses more quickly are still unknown [ 80 ].…”

“…Systemic acquired resistance (SAR) and ISR are two forms of induced resistance that have been characterized based on distinctions in signaling pathways and efficacy spectra [ 144 ]. ISR and SAR are two types of plant systemic resistance induced by non-pathogenic and pathogenic microorganisms, respectively [ 139 , 145 , 146 ]. They frequently overlap with interaction occurring between the two pathways [ 147 ].…”

“…ISR has emerged as a major method by which bacteria and fungi in the rhizosphere prepare the entire plant body for increased defense against a variety of diseases and insect herbivores [ 147 ]. Plants use long-distance systemic signaling to protect distal tissue after ISR activation, inducing quick and powerful immune responses against pathogen invasions [ 139 ]. BCAs can therefore suppress pests and diseases by activating the plant immune system [ 148 ].…”

“…can help plants to develop broad-spectrum disease resistance by stimulating defense responses [ 149 , 150 ]. Bacillus amyloliquefaciens , Bacillus atrophaeus , Bacillus cereus , Pseudomonas fluorescens , and other bacteria are efficient against fungal, bacterial, and viral invasion by ISR [ 139 ]. Trichoderma spp.…”

“…The transmission of ISR signaling was formerly thought to be dependent on JA and ET, but not on SA. The involvement of both the SA and JA/ET signaling pathways, as well as the regulatory roles of small RNA in ISR, has been revised in the previous decade [ 139 ]. T. harzianum T22 improves plant direct resistance against stink bug ( Nezara viridula ) feeding attack by increasing JA marker gene transcript levels early.…”