Biology subjects

Waelchli, J.

Publications and source records attributed to Waelchli, J..

6 recordsLinked to original sources

bioRxiv2026

Paralleled Dynamics of Arabidopsis Root Exudation and SynCom Assembly in a Controlled Environment

Plant roots host defined microbial communities that differ from those found in the surrounding soil and these communities shift dynamically in response to plant development and environmental changes. Whilst it is widely accepted that root exudates play a key role in the assembly and dynamics of root-associated microbial communities, the underlying mechanisms are not well understood. This is partly due to a lack of controlled experimental systems that monitor both exudate- and microbiome-dynamics simultaneously. Here, we compared two microcosm systems commonly used in either root microbiome (clay particle-based) or root exudate studies (glass bead-based) for their suitability to simultaneously monitor both aspects. We evaluated these systems based on plant performance, bacterial growth, and time-resolved community and exudate profiling. In both systems, we reveal an exudate effect, characterised by higher bacterial diversity and Pseudomonas abundances in proximity to plant roots. While clay particles impeded exudate recovery, even when plants were removed from microcosms for exudate collection, the glass bead set-up allowed us to uncover dynamic exudate shifts during bacterial community establishment. This highlighted a transient increase of glucosinolates upon root colonisation by initially dominant Pseudomonas species. Overall, the comparison proved only the glass bead-based semi-hydroponic system to be suitable for the paralleled study of exudate and root microbiome dynamics.

plant biology↗

bioRxiv2026

Soil iron drives beneficial maize microbiome feedbacks inrotations with wheat

BackgroundPlants change their surrounding soil microbiome by root exudates and such conditioned microbiomes impact the performance of the present as well as the next plant generation as for example in crop rotations. The big challenge is that such microbiome feedbacks are highly context-dependent, i.e. they vary in strength and direction dependent on the local soil environment - of which the driving factor(s) remain unknown. Including maize in crop rotations involves benzoxazinoids (BXs), which are exuded from roots and alter the soil microbiome, which in turn affects growth and defence of the following crop. ResultsHere, we grew wild-type and BX-depleted maize in the field to differentially condition their soil microbiome and we found varying feedbacks on wheat performance dependent on the local physicochemical soil parameters. Using multivariate, correlation and modelling approaches and including additional data from two previous field experiments, we identified plant-available (PA) iron to explain BX-dependent microbiome feedbacks on wheat. The BX-conditioned soil microbiome caused wheat to grow taller at low levels of soil PA-iron but smaller at high levels. This finding was generalized testing these maize microbiome feedbacks on the model plant Arabidopsis thaliana using soil batches containing different levels of iron. Consistent with wheat, a significant inverse relationship between soil PA-iron levels and plant growth was found. This relationship was experimentally validated with Arabidopsis grown at low levels of soil iron where iron supplementation abolished the beneficial feedback of the BX-conditioned soil microbiome. ConclusionTogether these findings revealed that beneficial microbiome feedbacks occur at low levels of plant-available iron, i.e. when plants grow in a suboptimal soil, but they are lost when plants are nutritionally well supported. These results underscore the importance of iron availability in soil for beneficial microbial feedbacks on plant growth and predict agronomic benefits of incorporating maize in crop rotations on low iron soils.

microbiology↗

bioRxiv2025

A TNL receptor mediates microbiome feedbacks in Arabidopsis

Plant performance depends on the soil microbiome. While microbiome feedbacks are well documented, the mechanisms by which plants perceive and mediate these feedbacks remain unclear. We established a framework using two distinct microbiomes in the same soil, where one led to enhanced growth of the Arabidopsis thaliana accession Col-0. Screening 410 accessions revealed substantial variation in growth feedbacks, which we used for genome-wide association mapping. We identified the immune receptor Mediator of Microbiome Feedback 1 (MMF1) as a candidate gene involved in microbiota feedbacks. Characterisation in the reference accession Col-0 revealed that mmf1 mutants lost the beneficial growth feedback, had an altered root bacterial community, and failed to induce a defence-related transcriptional response observed in wild-type plants. The discovery of MMF1 implies that integration of microbial signals optimises host microbiome composition and immune status to enhance growth.

plant biology↗

bioRxiv2023

Bacterial tolerance to host-exuded specialized metabolites structures the maize root microbiome

Plants exude specialized metabolites from their roots and these compounds are known to structure the root microbiome. However, the underlying mechanisms are poorly understood. We established a representative collection of maize root bacteria and tested their tolerance against benzoxazinoids, the dominant specialized and bioactive metabolites in the root exudates of maize plants. In vitro experiments revealed that benzoxazinoids inhibited bacterial growth in a strain- and compound-dependent manner. Tolerance against these selective antimicrobial compounds depended on bacterial cell wall structure. Further, we found that native root bacteria isolated from maize tolerated the benzoxazinoids better compared to non-host Arabidopsis bacteria. This finding suggests the adaptation of the root bacteria to the specialized metabolites of their host plant. Bacterial tolerance to 6-methoxy-benzoxazolin-2-one (MBOA), the most abundant and selective antimicrobial metabolite in the maize rhizosphere, correlated significantly with the abundance of these bacteria on benzoxazinoid-exuding maize roots. Thus, strain-dependent tolerance to benzoxazinoids largely explained the abundance pattern of bacteria on maize roots. Abundant bacteria generally tolerated MBOA, while low abundant root microbiome members were sensitive to this compound. Our findings reveal that tolerance to plant specialized metabolites is an important competence determinant for root colonization. We propose that bacterial tolerance to plant-secreted antimicrobial compounds is an underlying mechanism determining the structure of host-specific microbial communities. Significance StatementDiverse microbial communities colonize plant roots. They feed on carbon rich root exudates which contain a diverse mix of chemicals including primary and specialized metabolites. Here we show that specialized metabolites act as selective antibiotics to shape the root bacterial communities. By growing single isolates of maize root bacteria in the presence of benzoxazinoids in vitro, we find that the strains differ greatly in their tolerance to benzoxazinoids. Their different levels of tolerance largely explained their abundance on benzoxazinoid-exuding roots. Our work shows how plant specialized metabolites act to shape the maize root microbial community and thus deepened our mechanistic understanding of how plants shape their microbiome.

microbiology↗

bioRxiv2023

Soil chemical and microbial gradients determine accumulation of root exuded secondary metabolites and plant-soil feedbacks in the field

IntroductionHarnessing positive plant-soil feedbacks via crop rotations is a promising strategy for sustainable agriculture. Plants can influence soil properties including microbes by exuding specialized metabolites. However, the effects are often context dependent and variable. If and how local soil heterogeneity may explain this variation is unknown. Benzoxazinoids are specialized metabolites that are released in high quantities by cereals such as wheat and maize. Benzoxazinoids can alter rhizosphere microbiota and the performance of plants subsequently growing in the exposed soils and are thus an excellent model to study agriculturally relevant plant-soil feedbacks in the field, and to assess how soil factors affect their outcome. Materials & methodsTo understand the importance of local variation in soil properties on benzoxazinoid-mediated plant-soil feedbacks, we conditioned plots with wild-type maize and benzoxazinoid-deficient bx1 mutant plants in a grid pattern across an arable field. We then grew winter wheat across the entire field in the following season. We determined accumulation of benzoxazinoids, root-associated microbial communities, abiotic soil properties and wheat performance in each plot. We also determined benzoxazinoid conversion dynamics in a labelling experiment under controlled conditions, and then assessed associations between soil chemical variation and benzoxazinoid-mediated plant-soil feedbacks. ResultsAcross the field, we detected a marked gradient in soil chemical and microbial community composition. This gradient resulted in significant differences in benzoxazinoid accumulation. These differences were explained by differential benzoxazinoid degradation rather than exudation. Benzoxazinoid exudation modulated alpha diversity of root and rhizosphere bacteria and fungi during maize growth, but not during subsequent wheat growth, while the chemical fingerprint of benzoxazinoid accumulation persisted. Averaged across the field, we detected no significant feedback effects of benzoxazinoid conditioning on wheat performance and defence, apart from a transient decrease in biomass during vegetative growth. Closer analysis however, revealed pronounced feedback effects along the chemical and microbial gradient of the field, with effects gradually changing from negative to positive along the gradient. ConclusionOverall, this study revealed that plant-soil feedbacks differ in strength and direction within a field, and that this variation can be explained by standing chemical and microbial gradients, which strongly affect benzoxazinoid accumulation in the soil. Understanding within-field soil heterogeneity is crucial for the future exploitation of plant-soil feedbacks in sustainable precision agriculture.

plant biology↗

bioRxiv2022

Plant secondary metabolite-dependent plant-soil feedbacks can improve crop yield in the field

Plant secondary metabolites that are released into the rhizosphere alter biotic and abiotic soil properties, which in turn affect the performance of other plants. How such plant-soil feedbacks affect agricultural productivity and food quality in crop rotations is unknown. Here, we assessed the impact of maize benzoxazinoids on the performance, yield and food quality of three winter wheat varieties in a two-year field experiment. Following maize cultivation, we detected benzoxazinoid-dependent chemical and microbial fingerprints in the soil. The chemical fingerprint was still visible during wheat growth, while the microbial fingerprint was no longer detected. Benzoxazinoid soil conditioning by wild-type maize led to increased wheat emergence, tillering, growth and biomass compared to soil conditioning by bx1 mutant plants. Weed cover remained unaffected, while insect damage decreased in a subset of varieties. Wheat yield was increased by over 4% without a reduction in grain quality across varieties. This improvement was directly associated with increased germination and tillering. Taken together, our experiments demonstrate that plant secondary metabolites can increase yield via plant-soil feedbacks under agronomically realistic conditions. If this phenomenon holds across different soils and environmental conditions, optimizing plant root exudation could be a powerful, genetically tractable strategy to enhance crop yields without additional inputs.

plant biology↗