Project description:Diatoms, albeit being only distantly related with higher plants, harbour a plant-like cryptochrome (CryP) that was proposed to act as a photoreceptor required for the regulation of photosynthetic proteins. Importantly, plant cryptochromes are assumed to be involved in the regulation of developmental processes that are only needed in multicellular organisms; their role in the unicellular diatoms to date is mostly enigmatic. To elucidate the function of this plant-like cryptochrome in a unicellular species, we examined the role of CryP in the regulation of transcription in the diatom Phaeodactylum tricornutum by comparative RNA-seq of wild type and CryP knock-down mutants, under prolonged darkness and one hour after onset of blue light. In total, mRNAs of 12,298 genes were identified and more than 70% of the genes could be sorted into functional bins. We here show that CryP influences gene expression in three different ways: some genes are regulated by CryP under blue light only, others independent of the light condition and surprisingly some are regulated by CryP only in darkness. Changes under blue light included only around 4% of total genes, and genes regulated in any condition were distributed over almost all functional categories. Expression of photosynthesis genes was lowered by CryP under BL, in contrast to the overall enhancement in wild-type cells under the same conditions. Interestingly, CryP also exerted an influence on two other photoreceptors: the genes for phytochrome (Pt-DPH) and CPF1, another cryptochrome of Phaeodactylum tricornutum, were down-regulated by CryP independent of the light condition. However, the regulatory effects of the different photoreceptors on transcriptional output were independent. The influence of CryP on the expression of other photoreceptors hints to the existence of a regulatory signalling network in diatoms that includes several cryptochromes and phytochrome, whereby CryP acts as a regulator of transcript abundance under light as well as in darkness.
Project description:An experiment was performed to determine the similarities on the RNA level between different conditions where cell division stops in the diatom Phaeodactylum tricornutum. Many of these conditions also increase the accumulation of lipids within the cell or impair photosynthesis. The different metabolic responses were evaluated and the dataset was mined for potential transcriptional regulators of these changes. The experimental setup was as follows: Cells from the pennate diatom Phaeodactylum tricornutum were grown in ESAW medium under continous fluorescent light at 21C in baffled shakeflasks. Exponentially growing cells were harvested by centrifugation and washed twice in 21gr/L NaCL to remove nutrients. Cells were subsequently resuspended in the five different media/conditions (control, darkness, no nitrate, no phosphate, nocodazole).
Project description:We have investigated both the response to prolonged darkness and the re-acclimation to “moderate intensity” white irradiance (E = 100 µmol m-2 s-1) in the diatom Phaeodactylum tricornutum, using an integrated approach involving global transcriptional profiling, pigment analyses, imaging and photo-physiological measurements. The responses were studied during continuous white light, after 48 h of dark treatment and after 0.5 h, 6 h, and 24 h of re-exposure to the initial irradiance.
Project description:We have studied the transcriptional, metabolic and photo-physiological responses to light of different spectral quality in the marine diatom Phaeodactylum tricornutum through time-series studies of cultures exposed to equal doses of photosynthetically usable radiation of blue, green and red light. The experiments showed that short-term differences in gene expression and profiles are mainly light quality-dependent. Transcription of photosynthesis-associated nuclear genes was activated mainly through a light quality-independent mechanism likely to rely on chloroplast-to-nucleus signaling. In contrast, genes encoding proteins important for photoprotection and PSII repair were highly dependent on a blue light receptor-mediated signal. Changes in energy transfer efficiency by light-harvesting pigments were spectrally dependent; furthermore, a declining trend in photosynthetic efficiency was observed in red light. The combined results suggest that diatoms possess a light quality-dependent ability to activate photoprotection and efficient repair of photodamaged PSII. In spite of approximately equal numbers of PSII-absorbed quanta in blue, green and red light, the spectral quality of light is important for diatom responses to ambient light conditions.
Project description:Here we use a transcriptomic approach to investigate the molecular underpinnings of thermal acclimation in the model diatom species Phaeodactylum tricornutum by comparing the differential gene expression in cultures acclimated to sub-optimal, optimal, and supra-optimal temperatures (10, 20 and 26.5 °C, respectively).
Project description:Extensive gene methylation correlated strongly with transcriptional silencing and differential expression under specific conditions. DNA methylation and its role in gene regulation is conserved in stramenopile. Methylome of the whole genome of diatom phaeodactylum tricornutum.
