Impact of Quorum Sensing Molecules on Plant Growth and Immune System

Abstract

Bacterial quorum-sensing (QS) molecules are one of the primary means allowing communication between bacterial cells or populations. Plants also evolved to perceive and respond to those molecules. N-acyl homoserine lactones (AHL) are QS molecules, of which impact has been extensively studied in different plants. Most studies, however, assessed the interactions in a bilateral manner, a nature of interactions, which occurs rarely, if at all, in nature. Here, we investigated how Arabidopsis thaliana responds to the presence of different single AHL molecules and their combinations. We assumed that this reflects the situation in the rhizosphere more accurately than the presence of a single AHL molecule. In order to assess those effects, we monitored the plant growth and defense responses as well as resistance to the plant pathogen Pseudomonas syringae pathovar tomato (Pst). Our results indicate that the complex interactions between multiple AHL and plants may have surprisingly similar outcomes. Individually, some of the AHL molecules positively influenced plant growth, while others induced the already known AHL-priming for induced resistance. Their combinations had a relatively low impact on the growth but seemed to induce resistance mechanisms. Very striking was the fact that all triple, the quadruple as well as the double combination(s) with longchained AHL molecules increased the resistance to Pst. These findings indicate that induced resistance against plant pathogens could be one of the major outcomes of an AHL perception. Taken together, we present here the first study on how plants respond to the complexity of bacterial quorum sensing.

Microbial Derived Compounds, a Step Toward Enhancing Microbial Inoculants Technology for Sustainable Agriculture

“…For instance, while long chained AHLs induced tolerance to Pseudomonas syringae pv. in tomato, short chained AHLs had no effect on the same crop, even in combination with long chained AHLs ( Schenk et al, 2014 ; Shrestha et al, 2020 ). However, Liu et al (2012) , reported that, short chained (C6 and C8) AHLs enhanced elongation of the primary root in Arabidopsis thaliana , while long chains (C12 and C14) inhibited root elongation.…”

“…Until recently, the ability of LCO to directly enhance plant growth was unknown. Gram negative bacteria produce N-Acyl-L-Homoserine Lactones (AHLs) to monitor and manage their populations through quorum sensing ( Ortíz-Castro et al, 2009 ; Liu et al, 2012 , 2020 ; Schenk and Schikora, 2014 ; Hanifa et al, 2020 ; Shrestha et al, 2020 ). Some compounds, such as siderophores and bacteriocins, are produced to give the producer an upper hand during competition for resources such as nutrients and niche space, respectively.…”

“…It is a class IId bacteriocin, which inhibits growth of some bacteria, that could otherwise compete with it for resources ( Nazari and Smith, 2020 ). Whatever the reason for producing a particular compound may be, to the microbe, research has shown that plants have evolved mechanisms of perceiving some of these compounds ( Veliz-vallejos et al, 2014 ), and that they can actually enhance plant growth ( Banchio et al, 2009 ), under stressed and non-stressed conditions ( Dyachok et al, 2002 ; Duzan et al, 2005 ; Barriuso et al, 2008 ; Miransari and Smith, 2009 ; Schenk et al, 2012 ; Hanifa et al, 2020 ; Shrestha et al, 2020 ).…”

“…The mode of action may be influenced by factors such as plant and microbe genotype, environmental factors such as soil moisture and temperature, as well as the type and concentration of the compound ( D’Alessandro et al, 2014 ; Palmer et al, 2014 ; Shrestha et al, 2019 , 2020 ). For instance, while long chained AHLs induced tolerance to Pseudomonas syringae pv.…”

“…There is insufficient knowledge regarding how plants perceive some of these compounds ( Liu et al, 2012 , 2020 ; Shrestha et al, 2020 ), which limits their utilization as plant growth stimulants. For instance, in the case of AHLs, plant responses are thought to be are very specific and dependent on the length of the acyl moiety group ( Shrestha et al, 2020 ).…”