Chitin amendment in potting soil medium alters lettuce physiology and promotes defense response revealed by RNA sequencing

Chitin soil amendment is known to improve soil quality, plant growth and plant resilience. The first goal of this work was to study the effect of chitin soil amendment on the lettuce physiology. Secondly, we analysed the transcriptional reprogramming of lettuce roots in response to chitin treatment. Lettuce grown in chitin-amended soil had a higher flavonoid content two weeks after treatment. After four weeks of chitin treatment, lettuce exhibited a higher chlorophyll content, developed more leaves, and had a higher fresh weight at harvest. Over 300 lettuce genes were found to be significantly differentially expressed upon chitin soil treatment. Consistent with the phytiological changes observed, a GO-term enrichment analysis revealed statistical overrepresentation of GO terms linked to pigment metabolic processes, photosynthesis, and detoxification. Further analysis of the differentially expressed genes showed that the flavonoid pathway is mostly upregulated whereas the upstream phenylpropanoid pathway is mostly downregulated. Our data, in light to what is known in the litterature, suggest that the downregulation of the lignin biosynthetic pathway might lead to a change of flux to the flavonoid pathway – a hypothesis that we aim to test further. Since flavonoids play an important role in plant defense, our results are concurrent with available data describing higher resistance to diverse pathogens upon chitin soil amendment. Together, the work form this project will contribute to a better underdstanding of the modes-of-action of chitin soil amendment that could be used as a biostimulant for a more sustainable agriculture.

This project is supported by grant no. 189340 from the Swiss National Science Foundation (SNSF) and grant no. G063820N from the Fonds Wetenschappelijk Onderzoek (FWO)