Development of Cyclotella cryptica as new genetic model system for the study of photosynthesis and plastid biogenesis in marine diatoms

Diatoms are among the most successful photosynthetic eukaryotic microalgae in world’s oceans, derived from secondary endosymbiosis event. However, despite their ecological importance as primary producers and a growing biotechnological interest, current understanding about the regulation of diatom photosynthesis is still limited and fundamental questions about plastid biogenesis or activity remain unanswered. Furthermore, the use of genetic approaches for in-depth studies of key chloroplast functions is currently limited because the most studied diatom models are obligate phototrophs and those functions are essential for their survival. In order to fill this important knowledge gap, the centric diatom Cyclotella cryptica was selected as a novel model system for the study of photosynthesis, since it is the only diatom that combine the availability of genomic and genetic resources with the ability to grow heterotrophically in the absence of light, using glucose as a source of reduced carbon, thus potentially allowing the isolation of photosynthetic mutants. In this work, I developed a set of strategies based on CRISPR/Cas9 and homologous recombination to transform C. cryptica and respectively target plastid-localized nucleus-encoded and plastid-encoded genes essential for photosynthesis.