Genome editing of marine microalgae for characterization and metabolic engineering

Up to 2018 tens of thousands of transgenic organisms have been produced using gene transformation methods introducing random insertions of transgene material in the genomes of plant and animal cells. New technological developments based on guided insertions in given positions of the genome and simultaneously modification of homologous alleles have opened-up for functional studies and metabolic engineering. Methods like CRISPR/Cas9 and TALEN includes sequences guiding nucleases to the position where a mutation or some other type of modification is to be introduced. Marine microalgae are the major primary producers of the oceans. Over the last 10-20 year´s genome sequencing and development of the genetic tool-box and establishment of algal model species has opened for genetic manipulation of marine algae. One problem of using traditional genetic manipulation of diploid model marine microalgae is the absence in the lab systems of a method to produce homozygous modified cell lines. Breeding, forward genetic screens by random insertion, and chemical mutagenesis are therefore not applicable to the available diatom model species like Phaeodactylum tricornutum. Recently, methods for the use of tailored TALEN and CRISPR/Cas9 endonucleases have been developed for marine algae allowing targeted genetic modifications and the generation of knockout strains (1,2). Such stable mutant strains are extremely valuable for research. We have used CRISPR/Cas technology to knock-out genes involved in the assembly of the pigment-protein complex forming the light harvesting antennae where the aim is to produce cell lines having a higher light energy to biomass conversion rate. We also provide some new insight about genes regulating nutrient starvation responses in marine microalgae (3).