Trehalose mediates salinity-stress tolerance in a crustacean

Salinization poses an increasing problem worldwide, threatening freshwater organisms and raising questions about ability to adapt. We explore the mechanisms enabling a planktonic crustacean to tolerate elevated salinity. By gradually raising water salinity in clonal cultures from 185 Daphnia magna populations, we showed that salt tolerance strongly correlates with native habitat salinity, indicating local adaptation. A GWAS revealed a major effect of the Alpha,alpha-trehalose-phosphate synthase (TPS) gene, suggesting that trehalose production facilitates salinity tolerance. We found a positive correlation between water salinity and trehalose concentrations in tolerant animals, while intolerant animals failed to produce trehalose. Using CRISPR/Cas9, a silenced TPS gene supported the role of trehalose under salt stress. Our study highlights how a keystone freshwater animal adapts to salinity stress using an evolutionarily conserved mechanism known in plants and bacteria, but not in metabolic-active animals. HighlightsO_LISalinity tolerance is a locally adapted trait in Daphnia magna C_LIO_LIThe trehalose TPS gene shows a strong association with salinity tolerance C_LIO_LITrehalose content increases with water salinity allowing survival of tolerant genotypes C_LIO_LINon-functional TPS genes reduce salinity tolerance by preventing trehalose production C_LI