Knockout of a diatom cryptochrome by CRISPR/Cas9 causes an increase in light-harvesting protein levels and accumulation of fucoxanthin

Abstract

Diatoms are a promising source of fucoxanthin, a carotenoid that has many beneficial effects in human health. However, the gene encoding the last step of the fucoxanthin biosynthesis pathway in diatoms remains unidentified, and the molecular regulatory mechanisms are unknown. In this study, we show that cryptochrome CryP, a blue light-sensitive protein in the diatom Phaeodactylum tricornutum regulates fucoxanthin biosynthesis. CryP transcripts showed a diurnal rhythmic expression pattern; however, CryP protein showed high stability under different photoperiods. Furthermore, CryP not only regulates the expression of genes encoding carotenoid biosynthesis, but also affects the level of fucoxanthin chlorophyll a/c-binding proteins (FCPs). Upon knockout of the CryP gene, no change in cell morphology or growth was observed. However, both fucoxanthin content and FCP levels in P. tricornutum knockout lines increased greatly compared with the wild type. Our study is the first to report cryptochrome knockout in diatoms, which opens the possibility of fucoxanthin production through genome editing in P. tricornutum targeting known crucial steps.