Hypometabolism to survive the long polar night in the diatom Fragilariopsis cylindrus

Diatoms, the major eukaryotic phytoplankton in polar regions, are essential to sustain food webs. As such, it is fundamental to understand the physiological mechanisms and associated molecular basis of resilience to polar night of diatoms. Here, we report an integrative approach that reveals that in prolonged darkness, the cell enters a state of hypometabolism associated with reduced transcriptional activity during which no cell division occurs. Minimal energy is provided by respiration via alternative oxidase and progressive degradation of protein, carbohydrate and lipid stores. We also report internal structural changes that manifest the morphological acclimation of cells to darkness. Our results further indicate that immediately after returning to light, the majority of cells were able to use photoprotective mechanisms and resume photosynthesis. Divisions of surviving cells resumed at rates similar to those before darkness. Our study demonstrates the robustness of this species to prolonged darkness at low temperatures. Examination of gene expression (RNA-seq) from the acclimation phase in full light, in prolonged darkness and upon return to light. We analized two experiments: cells kept in the dark for one month (6 samples) or three months (17 samples). We analyzed three biological replicates per sample.