Heavy metal emissions from human activities are a significant environmental problem due to the high toxicity and persistence of these pollutants in soils, water bodies, and the atmosphere. Knowing how living organisms interact with these pollutants is vital to better understanding and managing the effects of pollution in the ecosystems, their components, and their functions. Plants in general and mosses in particular employ highly sophisticated molecular mechanisms to deal with environmental pressures like heavy metal contamination, drought or high levels of ultraviolet radiation. Therefore, they constitute an invaluable biological resource for study, as they are sessile and therefore unable to escape their surroundings. The Bryomics project used mosses to increase scientists’ understanding of the interactions between living organisms and heavy metal pollution and discover genes and gene products for developing biotechnological tools for air quality remediation and crop improvement. This research was undertaken with the support of the Marie Skłodowska-Curie programme.
A new approach
Researchers explored the mechanisms underlying intraspecific variation in heavy metal accumulation and tolerance in two terrestrial moss species with contrasting affinities to heavy metals. They were the copper-moss Scopelophila cataractae, which is mainly restricted to heavy metal enriched substrates, and the wider ranging Ceratodon purpureus, which can live on both polluted and unpolluted substrates. Scientists cultured the mosses in the laboratory using control, cadmium (Cd), and copper (Cu) enriched treatments. They determined the response to these pollutants by measuring Cd and Cu accumulation and plant performance. “We used epigenotyping by sequencing (epiGBS) to create the DNA methylation and genetic profiles of the samples; and used RNA sequencing to detect overall gene expression changes, and specific genes associated with Cu exposure,” says research fellow Teresa Boquete. DNA methylation is a process whereby a methyl group chemical tag can be added or removed from the DNA molecule, causing changes in gene expression without alteration of the DNA basic nucleotide sequence. DNA methylation patterns are flexible, dynamic, and susceptible to environmental stress, which provides plants with a mechanism that potentially allows them to rapidly and efficiently adapt to new environmental conditions. “The role of DNA methylation in the capacity of terrestrial mosses to deal with heavy metal pollution had never been studied before,” Boquete explains.
Benefits for crops and the environment
Results showed for the first time, the existence of intraspecific differences in tolerance to heavy metals in the metal specialist S. cataractae. “Such differences are related to the levels of contamination in their original environments and plants growing in the more contaminated soils showed greater tolerance,” comments Boquete. “We also demonstrated that in C. purpureus female plants are more tolerant to heavy metals than male plants.” These findings will help to give a clearer picture of issues such as contamination and crop production under suboptimal conditions. “The identification of candidate genes involved in heavy metal accumulation and tolerance can also be used to engineer plants that help clean up these contaminants from the environment, for example,” Boquete points out. Finally, BRYOMICS will form the basis for larger projects in which the ecological and evolutionary role of epigenetics could be assessed in depth using a wider range of bryophyte species.
BRYOMICS, heavy metal, mosses, DNA, copper (Cu), Scopelophila cataractae, Ceratodon purpureus, cadmium (Cd), epigenotyping by sequencing (epiGBS), RNA