Abstract
SummaryAureochromes represent a unique type of blue light photoreceptors that possess a blue light sensing flavin-binding LOV-domain and a DNA-binding bZIP domain, thus being light-driven transcription factors. The diatom Phaeodactylum tricornutum, a member of the essential marine primary producers, possesses four aureochromes (PtAUREO1a, 1b, 1c, 2). Here we show a dramatic change in the global gene expression pattern of P. tricornutum wild-type cells after a shift from red to blue light. About 75% of the genes show significantly changed transcript levels already after 10 and 60 min of blue light exposure, which includes genes of major transcription factors as well as other photoreceptors. Very surprisingly, this light-induced regulation of gene expression is almost completely inhibited in independent PtAureo1a knockout lines. Such a massive and fast transcriptional change depending on one single photoreceptor is so far unprecedented. We conclude that PtAUREO1a plays a key role in diatoms upon blue light exposure.
Highlights
Diatoms are unicellular photoautotrophic algae that gained their plastids from secondary endosymbiosis (Archibald, 2015), in which a heterotrophic eukaryote engulfed a primitive unicellular red alga and converted it into a plastid (Cavalier-Smith, 2013)
SUMMARY Aureochromes represent a unique type of blue light photoreceptors that possess a blue light sensing flavin-binding LOV-domain and a DNA-binding bZIP domain, being light-driven transcription factors
We show a dramatic change in the global gene expression pattern of P. tricornutum wild-type cells after a shift from red to blue light
Summary
Diatoms are unicellular photoautotrophic algae that gained their plastids from secondary endosymbiosis (Archibald, 2015), in which a heterotrophic eukaryote engulfed a primitive unicellular red alga and converted it into a plastid (Cavalier-Smith, 2013). Recent genome sequencing analyses showed that the diatom nuclear genome contains genes related to those of both plants and animals, including the green algal lineage, as well as a rather high percentage of bacterial genes due to lateral gene transfer (Bowler et al, 2008; Mock et al, 2017; Moustafa et al, 2009) In addition to their complex genome organization, diatoms differ in many aspects from green algae: Their cell walls consist of silica, the chloroplasts have a peculiar ultrastructure with four surrounding membranes, and the thylakoids are arranged in bands of three (Tanaka et al, 2015). The basic pathways for energy conversion and carbon partitioning show a number of unusual features compared with higher plants and green or red algae (Bailleul et al, 2015; Flori et al, 2017) These genetic and physiological characteristics of diatoms are in line with an extremely fast evolution (Sims et al, 2006), leading to an estimated 100,000 diatom species (Adl et al, 2012). The diversity and environmental adaptability might be explained by the increased genetic background that may allow enhanced and unknown environmental acclimation strategies against a broad spectrum of stressors, e.g., light intensity (Lepetit et al, 2013; Wilhelm et al, 2014), UV-B (Beardall et al, 2009), as well as carbon dioxide and iron limitation (Goldman et al, 2019; Kolody et al, 2019)
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