Tolerance and Metabolization of Host-Specific Specialized Metabolites by Maize and Arabidopsis Bacteria

MSc Caitlin Giroud

01/2024

Supervision: Dr. Lisa Thoenen, Prof. Klaus Schlaeppi

Abstract:

Plants exude secondary metabolites, which are known to structure their root microbiome. It has been shown that in maize root bacteria low abundant strains are less tolerant to the maize specific exudates than high abundant strains, which suggests adaptation to these exudates. However, the question arises whether we can also observe this host-specificity in tolerance and metabolization in another interaction of bacteria and exudates isolated from the same host plant, and how this suggested adaptation affects plant fitness. We attempt to answer this question by testing the maize root bacteria collection and the Arabidopsis bacteria collection in the maize-derived benzoxazinoid MBOA and in Arabidopsis exudates, the coumarins scopoletin and fraxetin. We tested the tolerance and metabolization of Arabidopsis and maize root bacteria and their host specialized metabolites in host and non-host context. In in vitro experiments we observed that native bacteria can tolerate the specialized metabolites from their host plant better than non-host bacteria. Furthermore, we observed that more maize root bacteria can metabolize MBOA than Arabidopsis bacteria can. These findings suggest that microbiome members are adapted to host-derived specialized metabolites in terms of tolerance and metabolization. Additionally, we investigated the ecological role of the suggested metabolic adaptation for host fitness through a plate plant growth assay. We observed that the presence of benzoxazinoids has a negative effect on non-benzoxazinoid producing plants in terms of shoot and root growth as well as root elongation. We propose that there is host specificity of bacterial strains to their host plant in terms of tolerance and metabolization of exudates, and we propose that this host specificity has an effect on the ecological fitness of the host plant.