Homoserine Lactones Influence the Reaction of Plants to Rhizobia

Abstract

Bacterial quorum sensing molecules not only grant the communication within bacterial communities, but also influence eukaryotic hosts. N-acyl-homoserine lactones (AHLs) produced by pathogenic or beneficial bacteria were shown to induce diverse reactions in animals and plants. In plants, the reaction to AHLs depends on the length of the lipid side chain. Here we investigated the impact of two bacteria on Arabidopsis thaliana, which usually enter a close symbiosis with plants from the Fabaceae (legumes) family and produce a long-chain AHL (Sinorhizobium meliloti) or a short-chain AHL (Rhizobium etli). We demonstrate that, similarly to the reaction to pure AHL molecules, the impact, which the inoculation with rhizosphere bacteria has on plants, depends on the type of the produced AHL. The inoculation with oxo-C14-HSL-producing S. meliloti strains enhanced plant resistance towards pathogenic bacteria, whereas the inoculation with an AttM lactonase-expressing S. meliloti strain did not. Inoculation with the oxo-C8-HSL-producing R. etli had no impact on the resistance, which is in agreement with our previous hypothesis. In addition, plants seem to influence the availability of AHLs in the rhizosphere. Taken together, this report provides new insights in the role of N-acyl-homoserine lactones in the inter-kingdom communication at the root surface.

N-Acyl-Homoserine Lactone Primes Plants for Cell Wall Reinforcement and Induces Resistance to Bacterial Pathogens via the Salicylic Acid/Oxylipin Pathway

“…AHLs with short chain (4 to 10 carbons) promote growth von Rad et al, 2008;Liu et al, 2012); C10-HSL was found to alter root architecture in Arabidopsis (Ortíz-Castro et al, 2008) and after substitution with a ketone group at the C3 position, the derivative, oxo-C10-HSL, was capable of inducing adventitious roots in mung bean (Vigna radiata) (Bai et al, 2012). On the other hand, long-chain AHLs (12 to 16 carbons) were shown to induce resistance in Medicago truncatula, Arabidopsis, and barley plants (Mathesius et al, 2003;Schikora et al, 2011;Zarkani et al, 2013). Besides the numerous effects of the different AHLs on plant development, a few studies have reported global transcriptional changes upon AHL treatment.…”

“…Usually bacteria produce high concentrations of quorum sensing molecules (e.g., AHLs) when growing in biofilms or mature colonies (above OD 600 of 0.5). The production of AHLs on root tissues by bacteria growing in biofilms has been shown (Zarkani et al, 2013), and the production of AHLs in biofilms on leaves is likely to occur, but has not been demonstrated yet. In addition, the application of commercial AHLs induced resistance against bacterial and fungal pathogens in Arabidopsis.…”

“…The first indication that AHLs play a role in plant immunity originated from a study of a Serratia liquefaciens-tomato (Solanum lycopersicum) interaction, in which the wild-type S. liquefaciens strain MG1, but not the corresponding AHLnegative mutant, induced resistance against the fungal pathogen Alternaria alternata (Schuhegger et al, 2006). Likewise, resistance against P. syringae induced by Ensifer meliloti (Sinorhizobium meliloti) in Arabidopsis plants depended on AHL accumulation (Zarkani et al, 2013). Usually bacteria produce high concentrations of quorum sensing molecules (e.g., AHLs) when growing in biofilms or mature colonies (above OD 600 of 0.5).…”

Rhodococcus erythropolis and Its γ-Lactone Catabolic Pathway: An Unusual Biocontrol System That Disrupts Pathogen Quorum Sensing Communication

“…Furthermore, plants seem to influence the amount of NAHSL in the rhizosphere: the presence of plants decreases the concentration of NAHSL in bacterial culture without having a major impact on bacterial growth. This diminution may be due to a quorum quenching activity of root exudates [113]. Finally, plants can also produce NAHSL analogs, which select and promote favorable rhizospheric microflora or, conversely, perturb quorum sensing by pathogenic populations [114].…”

Molecular Patterns of Rhizobacteria Involved in Plant Immunity Elicitation

“…A role of AHLs in plant immunity triggering has been established for several bacteria such Serratia liquefaciens inducing resistance in tomato against Alternaria alternata (Schuhegger et al, 2006) or Ensifer meliloti in Arabidopsis and it is obvious that these QS compounds are readily secreted by biofilm-forming colonies on roots (Zarkani et al, 2013). Interestingly, only long-chain AHLs (oxo-C14-HSL) can induce resistance in Arabidopsis while shorter derivatives promote plant growth (Schenk et al, 2014).…”