Establishment of genome editing techniques in the marine oleaginous diatom Fistulifera solaris for improved oil accumulation

Biofuel production using microalgae has attracted considerable attention owing to high growth rate and lipid accumulation properties. However, further enhancement in lipid productivity is required to render this economically feasible. CRISPR/Cas9, which is one of the powerful genome editing tools, is an essential technique that may solve this problem. The marine diatom Fistulifera solaris JPCC DA0580 is a promising candidate of the biofuel production, since it accumulates significant amount of lipids. However, genome editing techniques have not yet been established for F. solaris, which prevent the construction of valuable strains. In this study, CRISPR/Cas9-mediated specific gene knockout technique was established in F. solaris, through targeting adenine phosphoribosyl transferase gene (apt) and triacylglycerol (TAG) lipase gene (tgl1). Mutations in the target sequence were detected in apt- and tgl1-edited mutants. Moreover, the mutants showed distinct phenotypes, such as suppression of TAG degradation and resistance to 2-fluoroadenine. These results indicate the successful demonstration of CRISPR/Cas9-mediated genome editing in the oleaginous marine diatom F. solaris. Furthermore, oil degradation was successfully suppressed by knocking-out tgl1. The CRISPR/Cas9-mediated genome editing established in this study provides key molecular tools for both the basic biology and the future biotechnological applications of F. solaris, such as biofuel production.