An update on aureochromes: Phylogeny – mechanism – function

Abstract

Light is important for algae, as it warrants metabolic independence via photosynthesis. In addition to the absorption of light by the photosystems, algae possess a variety of specific photoreceptors that allow the quantification of the light fluxes as well as the assessment of light qualities. About a decade ago, aureochromes have been described in the xanthophyte alga Vaucheria frigida. These proteins represent a new type of blue light photoreceptor as they possess both a light-oxygen-voltage (LOV) domain for light reception as well as a basic region leucine zipper (bZIP) domain for DNA binding, indicating that they represent light-driven transcription factors. Aureochromes so far have been detected only in a single group of algae, photosynthetic stramenopiles, but not in any other prokaryotic or eukaryotic organisms. Recent biophysical work on aureochromes in the absence and the presence of DNA revealed the mechanism of allosteric communication between the sensor and effector domains despite their unusual inversed arrangement. Different molecular models have been proposed to describe the effect of light on DNA binding. Functional characterization of mutants of the diatom Phaeodactylum tricornutum, in which the aureochrome genes have been silenced or deleted, indicate that different aureochromes may have different functions, being involved in central processes like light acclimation and regulation of the cell cycle.

PhaeoNet: A Holistic RNAseq-Based Portrait of Transcriptional Coordination in the Model Diatom Phaeodactylum tricornutum

“…This is reminiscent of circadian gene expression patterns visualized in plant and other algal lineages (e.g., the green alga Ostreococcus and the dinoflagellate Lingulodinium), in which photosynthesis and plastid biogenesis proteins are either expressed at separate times of the day, or show different regulatory responses to circadian and light signals (Wang et al, 2005;Monnier et al, 2010;Noordally et al, 2013). Finally, the gene encoding the Aureochrome 2 protein (Phatr3_J8113), which lacks the conserved flavin-binding domain required for light perception (Takahashi et al, 2007;Kroth et al, 2017), falls within the greenyellow merged module of generally transcriptionally repressed proteins (Figure 3), underlining its independence of chloroplast functions.…”

Identification of circadian rhythms in Nannochloropsis species using bioluminescence reporter lines

“…Nannochloropsis oceanica encodes for three aureochrome genes (Vieler et al, 2012). Aureochromes are stramenopile-specific photoreceptors that have been shown to be involved in blue light-mediated photomorphogenesis in the Vaucheria genus and in the induction of cell division by blue light in diatoms (Takahashi et al, 2007;Kroth et al, 2017). Marine waters are enriched in blue light as light of longer wavelengths cannot penetrate water efficiently (Ragni and Ribera D'Alcal a, 2004;Kirk, 2011), and therefore blue light is likely to play a key role in signaling in marine organisms.…”

Identification of circadian rhythms inNannochloropsisspecies using bioluminescence reporter lines

“…N. oceanica encodes for three Aureochrome genes (Vieler et al , 2012). Aureochromes are stramenopile specific photoreceptors that have been shown to be involved in blue light mediated photomorphogenesis in the Vaucheria genus and in the induction of cell division by blue light in diatoms (Kroth et al , 2017, Takahashi et al , 2007). Marine waters are enriched in blue light since light of longer wave lengths cannot penetrate water efficiently (Kirk 2011, Ragni and Ribera D’Alcalà 2004) and therefore blue light is likely to play a key role in signaling in marine organisms.…”