Regional transcriptomic divergence reveals thermal adaptation mechanisms in the giant kelp Macrocystis pyrifera.

Understanding how gene expression shapes locally adapted phenotypes is pivotal in evolutionary ecology, yet it remains unexplored in keystone marine species like the giant kelp Macrocystis pyrifera. We hypothesized that juvenile sporophytes display transcriptomic signatures of thermal adaptation to their native Chilean habitats (from the regions of Atacama, Southern Chile and Magallanes). Individuals from each region were exposed to 8, 12, and 16 °C and their gene expression profiles were analysed via CLARA clustering and LEfSe discriminant analysis using a statistical framework designed to test for local adaptation, i.e. by comparing "Local versus Foreign" conditions and "Sympatric versus Allopatric" combinations of populations and thermal conditions. The number and biological roles of candidate adaptation genes (i.e. consistently up- or down regulated in the local or sympatric condition) varied across regions, reflecting divergent selective regimes. Individuals from Atacama specifically upregulated genes related to the synthesis of antioxidant compounds and intracellular protein turnover, when exposed to 16 °C. The population of Magallanes coped with low temperatures (i.e. 8 °C) using other mechanisms, such as the activation of the glyoxalase pathway and production of photoprotective pigments. These findings identify transcriptional patterns associated with regional thermal adaptation, providing candidate genes for future functional investigation.