Is Gene Duplication Driving Cold Adaptation in the Antarctic Green Alga <i>Chlamydomonas</i> Sp. UWO241?

Abstract

The frigid lakes and coastal waters of Antarctica are home to an assortment of eukaryotic algae, including psychrophiles, which can withstand intense cold but die at more moderate temperatures. Psychrophilic algae have evolved various survival strategies for coping with their unique environments. The polar diatom Fragilariopsis cylindrus, for example, has high allelic divergence, potentially helping it thrive in the fluctuating conditions of the Southern Ocean. Alternatively, the Antarctic sea ice green alga Chlamydomonas sp. ICE-L has an expanded set of gene families related to a psychrophilic lifestyle and encodes 12 ice-binding proteins. Here, we provide another take on Antarctic psychrophily by examining the ~212 Mb draft nuclear genome of Chlamydomonas sp. UWO241, which resides within the water column of a perennially ice-covered, hypersaline lake. Like its close relative ICE-L, UWO241 encodes a large number (≥37) of ice-binding proteins, putatively originating from horizontal gene transfer. Even more striking, UWO241 harbors hundreds of highly similar duplicated genes involved in diverse cellular processes, some of which we argue are aiding its survival in the Antarctic via gene dosage. Gene and partial gene duplication appear to be an ongoing phenomenon within UWO241, one which might be mediated by retrotransposons. Ultimately, we consider how such a process could be associated with adaptation to low temperatures and hypersalinity.