Importance of N-Acyl-Homoserine Lactone-Based Quorum Sensing and Quorum Quenching in Pathogen Control and Plant Growth Promotion

Abstract

The biological control of plant pathogens is linked to the composition and activity of the plant microbiome. Plant-associated microbiomes co-evolved with land plants, leading to plant holobionts with plant-beneficial microbes but also with plant pathogens. A diverse range of plant-beneficial microbes assists plants to reach their optimal development and growth under both abiotic and biotic stress conditions. Communication within the plant holobiont plays an important role, and besides plant hormonal interactions, quorum-sensing signalling of plant-associated microbes plays a central role. Quorum-sensing (QS) autoinducers, such as N-acyl-homoserine lactones (AHL) of Gram-negative bacteria, cause a pronounced interkingdom signalling effect on plants, provoking priming processes of pathogen defence and insect pest control. However, plant pathogenic bacteria also use QS signalling to optimise their virulence; these QS activities can be controlled by quorum quenching (QQ) and quorum-sensing inhibition (QSI) approaches by accompanying microbes and also by plants. Plant growth-promoting bacteria (PGPB) have also been shown to demonstrate QQ activity. In addition, some PGPB only harbour genes for AHL receptors, so-called luxR-solo genes, which can contribute to plant growth promotion and biological control. The presence of autoinducer solo receptors may reflect ongoing microevolution processes in microbe–plant interactions. Different aspects of QS systems in bacteria–plant interactions of plant-beneficial and pathogenic bacteria will be discussed, and practical applications of bacteria with AHL-producing or -quenching activity; QS signal molecules stimulating pathogen control and plant growth promotion will also be presented.

Wild Wheat Rhizosphere-Associated Plant Growth-Promoting Bacteria Exudates: Effect on Root Development in Modern Wheat and Composition

“…They have also been shown to have inter-kingdom signaling properties. They have positive effects on plant growth [ 78 , 79 ], and could be recognized by plant receptors and lead to modifications of plant gene expression [ 80 , 81 ].…”

“…The higher abundance of AHLs and cyclic peptides in the exudates collected in stationary phase ( Table S4 ) is consistent with the fact that part of the bacterial population was then engaged in a biofilm lifestyle, as also indicated by the presence of a veil on the walls of the Erlenmeyer flasks [ 85 ]. In addition to playing a role in quorum sensing, cyclic peptides can act as mimetics of phytohormones [ 79 , 86 , 87 ]. The CDP cyclo (L-Pro-4-OH-L-Leu) found in BPMP-PU-28 and BPMP-EL-40 growth supernatants is close to the CDP cyclo (L-Leu-L-Pro) identified in Bacillus gaemokensis and is shown to upregulate salicylic acid, ethylene and jasmonic acid signaling [ 88 ].…”

DSF-family quorum sensing signal-mediated intraspecies, interspecies, and inter-kingdom communication

“…QS signaling is not restricted to bacterial cell-to-cell communication but also allows communication between microbes and their hosts. This was best demonstrated in the context of interactions between AHL-producing bacteria and their associated plants [4]. Recently, DSF has also been demonstrated to mediate the communication between DSF-producing bacteria and the fungus Candida albicans, as well as plants, insects, and zebrafish (Figure 3, Key figure).…”

“…Research in recent decades has identified a rich inventory of QS signals and QS-regulated beneficial or competitive interactions [2]. Recent evidence shows that QS signaling is not limited to bacterial cell-cell communication but also allows communication between bacteria and their eukaryotic hosts [3][4][5]. Understanding the mechanisms and outcomes of QS signalmediated communication has important implications for appreciating host-pathogen interactions and, ultimately, may provide new targets and strategies for antimicrobial therapies that block or interfere with these communication networks.The diffusible signal factor (DSF) family represents an intriguing type of QS signal found in diverse Gram-negative bacteria.…”

Research Progress and Hopeful Strategies of Application of Quorum Sensing in Food, Agriculture and Nanomedicine

“…Moreover, the presence of luxR-solo or luxR-orphan genes were found in different plant-associated bacteria; it is a special condition in which the microbial chromosome harbors the luxR gene, while the gene encoding the corresponding luxI-type AHL synthase is missing. These so-called solo luxR genes may respond to exogenous AHL or even signals from plants, which open a new perspective on the understanding of interkingdom interactions [32].…”