Characterization of microbe-microbe, microbe-plant, and plant-plant interactions in the phyllosphere and their influence on microbiome function

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The SPP DECRyPT contributes to the elucidation of the role of the plant immune system in regulating microbiomes and their services to plants. This DECRyPT project investigates the reciprocal interactions between plant systemic immunity and the phyllosphere microbiome. We found that induced systemic resistance (ISR) triggered by interactions of Arabidopsis thaliana roots with beneficial microbes changes the composition of the leaf microbiota through plant-microbe-microbe interactions. These interactions resulted in the recruitment of new microbiota with plant growth-promoting properties to the leaf. In the work proposed for DECRyPT Phase-II we aim to characterize the molecular mechanisms underlying the microbe-microbe interactions we observed between Pseudomonas simiae and At-L-Sphere Flavobakterium Leaf82, which led to Leaf82 recruitment to A. thaliana leaves and growth promotion of the plants. Additionally, we aim to study the effects of the same bacteria and of additional plant-microbe interactions on the phyllosphere microbiome of Hordeum vulgare (barley). In barley, we will trigger ISR with synthetic communities (SynComs) of beneficial organisms, and study the modulating effects of the pathogen Bipolaris sorokiniana. We will also apply abiotic stress with the overarching aim of identifying phyllosphere microbiome changes in response to multiple stresses. In doing so, we follow the working hypothesis that robust microbiota changes that are associated with abiotic and beneficial and/or pathogenic biotic stimuli, likely fortify broad-spectrum stress tolerance in plants. By studying leaf microbiome dynamics in response to plant-plant interactions, we will further assess if long-distance interactions between plants stabilize the phyllosphere microbiome, harnessing plants and plant communities to better withstand pathogen pressure. The associated microbiota functions will be tested in SynCom experiments. Parallel analyses of plant growth parameters and of the gene expression profiles of both plants and microbiota will provide insights into the effects of microbiome dynamics on plant fitness and health. Together, the results of these experiments will provide insights into microbe-microbe, microbe-plant, and plant-plant interactions, and their role in recruiting and propagating [plant-fitness-promoting] microbiota functions to the phyllosphere.