Aureochromes are necessary for maintaining polyunsaturated fatty acid content inNannochloropsis oceanica

Abstract

Nannochloropsis oceanica, as other stramenopile microalgae, is rich in long-chain polyunsaturated fatty acids (LC-PUFA) such as eiconsapentaenoic acid (EPA). We observed that fatty acid desaturases (FAD) involved in LC-PUFA biosynthesis were among the strongest blue light induced genes in N. oceanica CCMP1779. Blue light was also necessary for maintaining LC-PUFA levels in CCMP1779 cells, and growth under red light led to a reduction in EPA content. 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. These proteins also contain a bZIP DNA binding motif and can act as blue light regulated transcription factors by associating with a E-box like motif, which we found enriched in the promoters of blue light induced genes. We demonstrated that, in vitro, two CCMP1779 aureochromes were able to absorb blue light. Moreover, the loss or reduction of any of the three aureochromes led to a decrease in the blue light specific induction of several FADs in CCMP1779. EPA content was also significantly reduced in NoAureo 2 and NoAureo 4 mutants. Taken together, our results indicate that aureochromes mediate blue light dependent regulation of LC-PUFA content in N. oceanica CCMP1779 cells.

Blue‐green light is required for a maximized fatty acid unsaturation and pigment concentration in the microalga Acutodesmus obliquus

“…Both effects are putatively related to rearrangement processes in the chloroplasts (Ho et al, 2014; Sánchez‐Saavedra & Voltolina, 2002). Higher unsaturated FA can be found in thylakoid membranes of chloroplasts in high percentages (Hugly & Somerville, 1992; Hultberg et al, 2014; Poliner et al, 2021). Therefore, this part of the light spectrum might increase the thylakoid membrane systems, with a concomitant elevation of pigments and specific PUFA in A. obliquus .…”

“…It is well known that these enzymes in plants and microorganisms are activated by environmental cues, such as light (Kis et al, 1998). In A. obliquus and the stramenopile microalga Nannochloropsis oceanica , this activation of FA desaturases is assumed to be triggered by blue‐green light exclusively (Helamieh et al, 2021; Poliner et al, 2021). This study on A. obliquus also supports this assumption.…”

“…This coincides with a higher observed content of photosynthetic pigments and xanthophylls upon blue light treatment (Fu et al, 2013; Ho et al, 2014; Sharmila et al, 2018). Furthermore, it was postulated that a maximum FA unsaturation in microalgae requires blue or blue‐green light (Helamieh et al, 2021; Poliner et al, 2021). However, the detailed activating waveband was only roughly estimated between 450 and 550 nm (Helamieh et al, 2021).…”

“…If this is the case, the increase of highly unsaturated FA should be coupled with increased photosynthetic pigments. Besides the effects of blue light, the impact of red light on many metabolic processes and the FA composition in eukaryotic microalgae is not yet well understood (Helamieh et al, 2021; Poliner et al, 2021).…”