Nannochloropsis oceanica, as other stramenopile microalgae, is rich in long-chain polyunsaturated fatty acids (LC-PUFA) such as eiconsapentaenoic acid (EPA). PUFAs have been proposed to protect membrane systems against oxidative damage and are important nutrients for human health. We observed that blue light is necessary for maintaining LC-PUFA levels in N. oceanica cells, and growth under red light leads to a reduction in EPA content. To investigate the mechanism of blue light regulation of EPA content we carried out a transcriptome analysis of dark adapted cells treated with short pulses of either red or blue light. We had previously identified the fatty acid desaturases (FAD) involved in LC-PUFA biosynthesis in N. oceanica CCMP1779; we now observed that the corresponding FAD genes are specifically induced by blue but not red light in this alga. Aureochromes are stramenopile specific proteins that contain a light-oxygen-voltage-sensing (LOV) domain that associates with a flavin mononucleotide and is able to sense blue light. They also contain a bZIP DNA binding motif and can act as blue light regulated transcription factors. We demonstrate that, in vitro, N. oceanica Aureochromes are able to absorb blue light. Moreover, the loss of or a reduction in any of the three N. oceanica Aureochromes led to a reduction in the blue light specific induction of several FADs in N. oceanica. Taken together, our results indicate that Aureochromes mediate blue light dependent regulation of LC-PUFA content in N. oceanica cells.
Coauthors: Eric Poliner – Michigan State University;Linsey Newton – Michigan State University