LAUSR

Abstract Adverse changes in vegetation occur as the effect of the progressive drying of peatlands, leading to the disappearance of peat mosses (Sphagnum), a key component of these ecosystems. We report gene expression divergence for two putative ecotypes of S. denticulatum collected from contrasted habitats under the threat of drought. We used cDNA-amplified fragment length polymorphism (cDNA-AFLP) as the first screening method. We then used real-time, quantitative PCR to identify genes whose transcription changes in response to drought and rehydration treatments. Using 133 of 900 pretested cDNA-AFLP primer combinations, we have identified 949 drought-induced transcript-derived fragments, 6 (0.6%) of which are significantly differentially expressed genes (DEGs) in the putative ecotypes. We cloned and sequenced 378 fragments using designed fragment-specific primers. Transcription patterns were quantified for 21 target genes using qRT-PCR. When upregulated under drought, nine genes showed fold changes in a range of 4.64–150.03. The DEGs represented functional categories including protein/nucleotide binding, catalytic activity, transporter activity, and enzyme regulation activity. These genes are known to be involved in various metabolic pathways and physiological processes which emphasize the complexity of plant response to stress. Most of the significant differences in transcription patterns were evident in the aquatic plants, suggesting induced responses to drought in these plants. The expression was significantly less pronounced in the terrestrial plants, indicating that they are preconditioned to withstand drought stress. We detected positive selection on individual codons for specific branches using the ratio of substitution rates at nonsynonymous and synonymous sites (dN/dS). For the first time, this study provides insight into the genetic basis of the putative adaptive evolution in Sphagnum and allows for the discovery of genes involved in drought stress response.