Résumé
The plant growth-promoting rhizobacterium Pseudomonas simiae WCS417 (WCS417) has a positive effect on Arabidopsis thaliana growth and triggers a broad-spectrum induced systemic resistance (ISR) in the leaves. Earlier, we identified a link between the root-specific transcription factor MYB72, coumarin biosynthesis and metabolism, and ISR. Coumarins are Fe deficiency-induced fluorescent phenolics that help plants to acquire Fe from recalcitrant soils. Overexpression of a root coumarin metabolism gene induced a constitutive ISR response, while knockout of this gene resulted in a loss of ISR, indicating that coumarins play a role in the onset of ISR. To further elucidate this mechanism, we studied where coumarins accumulate in the roots and whether root colonization by WCS417 can affect coumarin accumulation in the leaves. To study the spatial accumulation of coumarins in the root, we employed multispectral imaging and found that WCS417 induces a coumarin accumulation pattern that differs from that of Fe deficiency. We then performed HPLC-FLD to investigate whether coumarins accumulate also in leaves upon root inoculation with WCS417. Interestingly, in both tissues we observed a strong transient coumarin accumulation, peaking at 5 days upon treatment. This indicates that coumarin accumulation might play a direct role in the onset of ISR in the shoot, potentially as a root-to-shoot signal. Next, we will investigate coumarin trafficking and their molecular effects in the shoot.