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.
Highlights
Application of beneficial microbes triggers an enhanced resistance state, termed as induced systemic resistance (ISR), in the host, against a broad range of pathogens
We summarize the recognition of beneficial microorganisms and early events that occur during induced systemic resistance, highlighting reactive oxygen species burst, callose deposition that can inhibit the infection and expansion of pathogens, calcium signaling, and transcriptional factors, that play a significant role in regulating the expression of downstream defense-related genes and diseases control
Colonization of plant growth-promoting rhizobacteria (PGPR) on the roots requires local suppression of pattern-triggered immunity (PTI) to protect the PGPR from MAMP-triggered antimicrobial compounds, which suggests a co-evolution leading to regulation of the host’s immune system after recognition of specific signals from beneficial microbes. These results demonstrated that beneficial microbes and their elicitors could induce plant defense responses, yet the mechanism of plant-specific recognition of beneficial microorganisms and immunity responses, that distinguish beneficial microorganisms from pathogens, is still unclear
Summary
With the rapid growth of the world’s population, people’s demand for agricultural products is increasing. In 1991, three research groups independently and evidenced that beneficial microbes enhanced plant immunity by ISR [12,13,14] Among these three groups, Kloepper et al found that plant growth-promoting rhizobacteria (PGPR) could induce cucumber systemic resistance to Fusarium-wilt, bacterial angular leaf spot, root-knot nematode, and cucumber mosaic cucumovirus [13,15,16,17,18]. We summarize the recognition of beneficial microorganisms and early events that occur during induced systemic resistance, highlighting reactive oxygen species burst, callose deposition that can inhibit the infection and expansion of pathogens, calcium signaling, and transcriptional factors, that play a significant role in regulating the expression of downstream defense-related genes and diseases control.
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