Molecular basis of intraspecific differentiation for heavy metal tolerance in the copper moss Scopelophila cataractae

The remarkable capacity of bryophytes to tolerate extremely challenging abiotic conditions allows us to enhance our understanding of the diversity of molecular mechanisms involved in plant stress response. Here, we used next generation sequencing to study DNA methylation and gene expression changes in plants from four populations of the metallophyte moss Scopelophila cataractae experimentally exposed to either Cd or Cu. These populations previously showed differences in tolerance to both metals, so here, we aimed to investigate the molecular basis of this phenotypic differentiation. We found no evidence of genetic differentiation among the populations studied. The epigenetic data, however, showed limited but significant population-specific changes in DNA methylation in response to both metals. Exposure to acute Cu stress in the laboratory led to the downregulation of genes involved in heavy metal tolerance in both the more and the less tolerant populations, but this response was quantitatively higher in the most tolerant. We propose that chronic exposure to varying levels of heavy metals in the field led to potentially non-genetically-based intraspecific differentiation for heavy metal tolerance in S. cataractae. The most tolerant plants invested more in constitutive protection and were more efficient at entering a conservative state when faced with acute Cu stress.