Gene expression during the formation of resting spores in the marine diatom Chaetoceros socialis

Abstract BackgroundDormancy is widespread in both multicellular and unicellular organisms. Among diatoms, unicellular microalgae at the base of all aquatic food webs, several species produce dormant cells (spores or resting cells) that can withstand long periods of adverse environmental conditions. ResultsWe present the first gene expression study during the process of spore formation in the marine planktonic diatom Chaetoceros socialis. Spore formation was induced by nitrogen depletion. Genes related to photosynthesis and nitrate assimilation, including high-affinity nitrate transporters (NTRs), were downregulated. While the former result is a common reaction among diatoms under nitrogen stress, the latter seems to be exclusive of the spore-former C. socialis. The upregulation of catabolic pathways, such as tricarboxylic acid cycle, glyoxylate cycle and beta-oxidation, suggests that this diatom could use lipids as a source of energy during the process of spore formation. Furthermore, the upregulation of a lipoxygenase and several aldehyde dehydrogenases (ALDHs) advocates the presence of oxylipin-mediated signalling, while the upregulation of genes involved in dormancy-related pathways conserved in other organisms (e.g. serine/threonine-protein kinases TOR and its inhibitor GATOR) provides interesting avenues for future explorations. ConclusionsOur results demonstrate that the transition from an active growth phase to a resting one is characterized by marked metabolic changes and provide evidence for the presence of signalling pathways related to intercellular communication.