Genetic engineering of dinoflagellate algae and the lethality of an introduced plastid terminal oxidase

Dinoflagellate algae are a diverse group of single-celled eukaryotes, often living in marine environments. The majority of species are entirely free-living, but many can become symbionts with corals, jellyfish and other marine organisms. With rising sea temperatures, the function of the dinoflagellate photosynthetic machinery, and the redox state of the photosynthetic electron transport chain are impaired. This photosynthetic impairment is likely to be an important cause of coral bleaching. In the chloroplasts of plants and many algae, disturbance of the chloroplast redox state can be in part alleviated by the Plastid Terminal Oxidase protein (PTOX). Here, we made use of our newly developed genetic modification tools in the free-living dinoflagellate species Amphidinium carterae, which is found in both in temperate and tropical waters. We test if the introduction of PTOX to the chloroplast would allow A. carterae to withstand temperature stress. We find that the expression of the PTOX gene caused a lethal phenotype. Genetic engineering of dinoflagellate algae has long been problematic, and the ability to express heterologous proteins represents a significant advance in the long-term quest to engineer a heat-tolerant dinoflagellate.