Assessment of transcriptional reprogramming of lettuce roots in response to chitin soil amendment

Abstract

Chitin soil amendment is known to improve soil quality, plant growth and stress resilience, but the underlying mechanisms are not well understood. In this study, we monitored chitin’s effect on lettuce physiology every two weeks through an eight-week growth period, analyzed the early transcriptional reprogramming and related metabolomic changes of lettuce, in response to crab chitin treatment in peat-based potting soil. In commercial growth conditions, chitin amendment still promoted lettuce growth, increased chlorophyll content, the number of leaves and crop head weight from week six. The flavonoid content in lettuce leaves was altered as well, showing an increase at week two but a decrease from week six. Transcriptomic analysis showed that over 300 genes in lettuce root were significantly differentially expressed after chitin soil treatment. Gene Ontology-term (GO) enrichment analysis revealed statistical overrepresentation of GO terms linked to photosynthesis, pigment metabolic process and phenylpropanoid metabolic process. Further analysis of the differentially expressed genes (DEGs) showed that the flavonoid pathway was mostly upregulated whereas the bifurcation of upstream phenylpropanoid pathway towards lignin biosynthesis was mostly downregulated. Metabolomic analysis revealed the upregulation of salicylic acid, chlorogenic acid, ferulic acid, and p-coumaric acid in chitin-treated lettuce seedlings. These phenolic compounds (PCs) mainly influence the phenylpropanoid biosynthesis pathway and may play important roles in plant defense reactions. Our results suggest that chitin soil amendments might activate induced resistance by priming lettuce plants and promote lettuce growth via transcriptional changes.

Soil Type and Associated Microbiome Influence Chitin's Growth Promotion Effect in Lettuce

“…Chitin's effect on promoting lettuce growth in PS has been reported previously (Debode et al 2016;Li et al 2023). However, lettuce is mainly cultivated in MS, for which the effectiveness of chitin was not explored yet.…”

“…For the targeted metabolomics analysis the same targets were used which were previously reported to be altered upon chitin soil amendments (Li et al 2023). For both targeted and untargeted metabolomics analysis, the metabolites extraction was performed using the method described previously with slight modification (Li et al 2023).…”

“…For the targeted metabolomics analysis the same targets were used which were previously reported to be altered upon chitin soil amendments (Li et al 2023). For both targeted and untargeted metabolomics analysis, the metabolites extraction was performed using the method described previously with slight modification (Li et al 2023). Briefly, 50 µL internal standard (daidzin, 100ng µL -1 ) and 10 mL pure methanol (ULC/MS grade absolute methanol) was added to 500 mg of freeze-dried tissue powder, vortexed for 1 min, then sonicated using an Elma Transsonic digital S unit (Elma Schmidbauer GmbH, Singen, Germany) at 40 kHz for 15 min.…”

“…Previous research has demonstrated that chitin amendment of peat substrate (PS) could significantly promote the crop production of lettuce (23.8% to 89.5%) (Debode et al 2016;Li et al 2023). Moreover, addition of chitin into PS potentially enriches the population of plant growth promoting rhizobacteria and fungi (De Tender et al 2019;De Tender et al 2023).…”

“…Moreover, addition of chitin into PS potentially enriches the population of plant growth promoting rhizobacteria and fungi (De Tender et al 2019;De Tender et al 2023). Also, chitin / chitosan addition could affect lettuce seedling's growth on transcriptional and metabolite level, modifying the accumulation of several phenolic acids and plant hormones, which might promote lettuce growth and disease resistance (Pusztahelyi 2018;Li et al 2023).…”