| Organisms encounter environmental stressors such as nutrient and water deficiencies, salinity, UV, and temperature extremes on a regular basis. Individuals and organisms respond differently to different stressors, some are very sensitive while others have adapted mechanisms for resilience. Sea-ice diatoms thrive under extreme conditions, overcoming freezing temperatures that form internal ice crystals, shut-down metabolic activity, and create cell-wide oxidative stress in most organisms; but they also synthesize a sulfur compound, dimethylsulfoniopropionate (DMSP), that is believed to help mitigate cellular damage through its proposed antioxidant, antifreeze, and salt buffering properties. DMSP also plays important roles in carbon, sulfur and climate cycles. Understanding physiological regulation of DMSP production is fundamental to understanding its role in both cellular and global processes. To date, the specific enzymes controlling DMSP synthesis remain unknown. To overcome this critical gap in knowledge a proteomics approach was undertaken to identify protein changes associated with salinity-induced DMSP elevations in the sea-ice diatom, Fragilariopsis cylindrus (CCMP 1102). The overarching hypothesis was that increases in enzymes associated with the proposed algae methionine-DMSP synthesis pathway would be identified in association with environmentally-induced elevation of intracellular DMSP. Proteomics identified 18 proteins within the four enzyme classes of the proposed DMSP pathway. While sequence homology assigned most to other well-characterized metabolic pathways, five were poorly characterized and therefore presented as candidate DMSP synthesis enzymes. Transcriptional studies found temporal elevations of all candidate DMSP synthesis genes corresponded with salinity-induced DMSP elevations. Transcript studies under nitrogen-induced DMSP accumulation, however, indicated differential regulation of pathway enzymes and perhaps decreased DMSP catabolism was also contributing to observed elevations. |
