Unknown,Transcriptomics,Genomics,Proteomics

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Genome-wide profiling of responses to cadmium in the diatom Phaeodactylum tricornutum

ABSTRACT: The only group of organisms in which a biological function for cadmium has been shown is the diatoms, which are unicellular phytoplankton. Yet diatoms exhibit similar sensitivity to Cd as other groups of phytoplankton. We have investigated responses of Cd on molecular, metabolic and physiological levels in the diatom Phaeodactylum tricornutum. P. tricornutum apparently has a high tolerance to Cd; only minor responses were observed on growth, pigment and transcriptional changes at cadmium concentrations of 123 µg/l. No significant changes in chlorophyll and xanthophyll levels were observed, and the very few transcripts affected strongly indicate that the cells were able to respond to the increased Cd2+ levels without changing proteins levels. At 10 times this concentration, 1230 µg/l, a much clearer response was observed, including transcripts encoding proteins involved in metal transport, cell signalling and detoxification processes. Our results point towards putative pathways for the removal or detoxification of Cd and its metabolites, as well as a possible Cd uptake mechanism. We predict that ATPase5-1B is involved in removal of Cd by pumping Cd2+ ions out of the cell, whereas VIT1/CCC1 sequesters Cd2+ in the vacuole. Cultures of Phaeodactylum tricornutum were treated with two concentrations of Cd2+, 123 µg/l and 1230 µg/l. The reference samples were grown in artificial seawater base AK modified with added f/2-medium nutrients. Three biological replicates were harvested for all samples.

ORGANISM(S): Phaeodactylum tricornutum

SUBMITTER: Per Winge

PROVIDER: E-GEOD-31131 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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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. Continuous, axenic culturing of P. tricornutum was done as described in Nymark et al. (2009). The cultures were incubated at 15M-BM-0C under cool white fluorescent light (Philips TLD 36W/96) providing a scalar irradiance (EPAR) of 100 M-NM-<mol m-2 s-1 under continuous white light (CWL) conditions. Upon the onset of the experiment the cultures were synchronized by 48 h dark-treatment (D48). Thereafter the algae were exposed to blue light (BL), green light (GL) or red light (RL) provided by a waveband specific LED panel (SL3500, Photon Systems Instruments). The algae were exposed to 0.5 h, 6 h or 24 h of: 1) 230 M-NM-<mol m-2 s-1 of RL, 2) 100 M-NM-<mol m-2 s-1 of GL, 3) 50 M-NM-<mol m-2 s-1 of BL or 4) 100 M-NM-<mol m-2 s-1 of WL respectively. Three biological replicas for each of the treatments were harvested. Data for the white light exposure and 48h dark treatment is described in GSE42039, PMID: 23520530.

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Genome-wide profiling of responses to cadmium in the diatom Phaeodactylum tricornutum

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