OUTER MEMBRANE VESICLES: A NEW PLAYER IN PLANT-PATHOGEN INTERACTIONS

The release of outer membrane vesicles (OMV) by Gram-negative bacteria is reported to have multiple functions, such as toxin delivery, cell-cell communication and host-pathogen interactions (Ellis and Kuehn, 2010). So far, most of the research regarding OMVs was done on bacteria pathogenic to animals and humans. To study the interactions between OMVs and plants, we isolated OMVs from plant-pathogenic bacteria, such as Xanthomonas campestris and Acidovorax citrulli, and examined their effect on Arabidopsis thaliana plants. To see whether OMVs elicit the plant`s immune system, we treated the plants with OMVs and quantified, using qRT-PCR, the expression of two defense marker genes (FRK1 and At5g57220). The expression of both genes was significantly higher in OMV-treated plants, compared to the control. We also used the reactive oxygen species (ROS) assay, which showed that OMVs elicited ROS production. To find which receptors are involved in sensing OMVs, we used various immune receptor gene mutants. A significantly lower marker genes’ expression occurred in bak1-5 mutant, showing the importance of co-receptor BAK1 in OMV sensing. To examine if this immune response affects bacterial proliferation in planta, we pretreated A. thaliana with OMVs, a day before inoculation with Pseudomonas syringae pv. tomato. Plants pretreated with OMVs had significantly lower bacterial titer, compared with mock-pretreated plants. To determine the proteinaceous cargo of OMV we used LC-MS/MS. Hundreds of proteins were identified, many of which were uncharacterized and some had immunogenic properties. To conclude, in this research we started studying plant-OMV interactions, a topic that is very poorly described. Future plans include sequencing the plant`s transcriptome, in order to get a broader picture of the plant`s response to OMV.