Physiological and transcriptomic response of dinoflagellate Gymnodinium catenatum to nitrate deficiency

Integrated physiological and transcriptomic analysis reveals mechanism of planktonic dinoflagellate Gymnodinium catenatum response to heat and cold stress

The paralytic shellfish toxin-producing dinoflagellate Gymnodinium catenatum is distributed worldwide and often forms massive blooms in coastal waters, which pose a major threat to economic development and human safety. Temperature is among the factors influencing the growth and toxin production of HABs species. However, the physiological and molecular responses of G. catenatum to cold and heat stress need more investigations. Here, we compared the growth, toxin production, and transcriptomes of G. catenatum (Xiamen Bay, China) at different temperatures. Both cold (15°C) and heat (30°C) stress suppressed the growth and chlorophyll a content of G. catenatum. Transcriptomic analysis revealed that carbon from growth-related processes was redirected toward fatty acid synthesis to enhance energy storage under cold stress; up-regulated cold shock proteins and RNA-binding proteins maintained the stability of nucleic acids. Antioxidant activity was enhanced under heat stress with energy and carbon skeletons derived from the light reaction and starch and leucine degradation. The increase in toxin production probably stemmed from the enhanced transcription of core toxin synthesis genes and the inhibition of cell division under cold stress, whereas heat stress markedly enhanced the expression of genes involved in toxin synthesis. This enhanced the ability of G. catenatum to survive over a range of temperatures, and the increased frequency and toxicity of its blooms have significant ecological and economic implications under future global warming.