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Abstract:
Members of the genus Pseudomonas often dominate the phyllosphere of A. thaliana in the wild. A multi-year survey of Pseudomonas in local A. thaliana populations revealed co-colonization of numerous strains in the same population, and even within the same plant (Karasov et al., 2018). We are examining the interactions of such strains both with each other and with a panel of local A. thaliana genotypes, by infecting soil-grown A. thaliana accessions with three synthetic communities: pathogens only, commensals only (both defined based on single strain-plant interactions in vitro), and a mixture of both. Strains were genetically barcoded, allowing precise quantification of all strains. While infections with the pathogen community reduced the weight of all plant genotypes, infections with the mixture of pathogens and commensals gave a host genotype-dependent result; there was no weight reduction in any genotype but one. Pseudomonas strain abundance data implied that commensals suppressed all
pathogenic strains except one. By associating bacterial composition with the plant weight, we managed to find that genotype-dependent control of the unsuppressed strain could explain differential commensal protection. Collectively, our results demonstrate the complexity of interactions among local Pseudomonas strains that co-occur in nature as well as the effect of the host genotype on these interactions. We are now
investigating how which genes are responsible for host and bacterial effects.
