Microplastics in the Soil at Sub-Toxic Concentrations Cause Metabolic Changes Decreasing Fungal Pathogen Susceptibility in Arabidopsis thaliana

To unravel the complex interactions between microplastics (MPs), plants, and pathogens, Arabidopsis thaliana plants were grown for 3 weeks in soils containing polyethylene terephthalate (PET) or polyvinyl chloride (PVC) MPs (0.2% and 0.5% w/w), and leaves were then exposed to the PAMP (Pathogen-Associated Molecular Pattern) protein cerato-platanin (CP) or Botrytis cinerea conidia. PET caused a stimulation of stomatal conductance, and PVC decreased the aboveground biomass of A. thaliana plants. PVC (0.2%) triggered a primed state in A. thaliana, enhancing its response to B. cinerea infection and cerato-platanin. This was demonstrated by decreased lesion size, enhanced ROS generation, and elevated camalexin synthesis following PAMP elicitation, and increased levels of defensive isothiocyanate and phenylpropanoid metabolites. Our results indicate that MPs also affect soil structure, ionome balance, and specialised metabolite accumulation. However, MPs did not provide an unambiguous response, underscoring challenges in formulating a model of plant response to MPs when exposed to pathogens.