Directed selection of suppressive rhizosphere microbiome community helps to overcome the growth-defence trade-off

To be closer to solve the mystery of plant growth inhibition by SA, we aim to answer the following questions:-When does SA start to be harmful to plant growth?-How high SA impacts the diurnal carbon balance?-How high SA affects the metabolic flow?In particular, assimilation of CO2 into the cuticle, inhibition of anthocyanins, biosynthesis and accumulation of lignin.-Does SA cross-talk with auxin contribute to SA-caused growth inhibition?Rhizosphere microbiome contributes to nutrient acquisition, protection against biotic and abiotic stresses and, ultimately, changes in the development and physiology of plants.We followed the microbial dynamics in the soil of Arabidopsis thaliana infected with the foliar pathogen Pseudomonas syringae pv.tomato DC3000 (Pst).Soil microbial communities were selected using a directed or undirected (i.e.natural) selection approaches .Plants were iteratively cultivated on a pasteurized soil inoculated with the soil microbial community of the previous iteration isolated from the rhizosphere of plants infected with Pst (pst-, or control line) or not (mock-or un-conditioned line).Out of the infected plants, two groups were additionally designated based on disease manifestation in leaves: suppressive and conducive line.Modification of soil microbial communities was assessed through an amplicon-based metagenomic analysis targeting bacterial and fungal diversity.Plant fitness, rosette size and transcript abundance of stress hormone related genes were also analysed.At the tenth and eleventh iterations, we observed a reduction in disease severity in pst-lines as compared to mock-lines, accompanied with the smaller rosette size in the line deriving from the natural selection, but not in the directly selected suppressive line.These changes were associated with (i) altered transcript abundance of genes associated with signaling pathways of salicylic, jasmonic and abscisic acid (ii) a shift in soil bacterial, but not in fungal, composition.Our proof-of concept study shows potential of targeting plant-soil feedbacks to enhance soil suppressiveness against foliar pathogens.