The widespread coccolithophore
- NSF-PAR ID:
- Publisher / Repository:
- Date Published:
- Journal Name:
- Environmental Microbiology
- Page Range / eLocation ID:
- p. 1847-1860
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Emiliania huxleyiis a calcifying haptophyte, contributing to both the organic and inorganic marine carbon cycles. In marine ecosystems, light is a major driver of phytoplankton physiology and ultimately carbon flow through the ecosystem. Here, we analysed a Lagrangian time‐series of metatranscriptomes collected in the North Pacific Subtropical Gyre (NPSG) to examine how in situpopulations of modulate gene expression over day–night transitions. Many E. huxleyi contigs had a diel expression pattern, with 61% of contigs clustering into modules with statistically significant diel periodicity. Contigs involved in processes that build up energy stores, like carbon fixation and lipid synthesis, peaked around dawn. In contrast, contigs involved in processes that released energy stores, like respiration and lipid degradation, peaked mid‐day and towards dusk. These patterns suggest an orchestrated cycle of building, then consuming energy stores in E. huxleyi populations in the NPSG. Selected contigs related to the cell cycle also exhibited significant diel periodicity consistent with phased modulations of division observed in culture. Overall, these patterns of gene expression suggest a daily metabolic cascade that could contribute to both organic and inorganic carbon flow in this nutrient depleted ecosystem. E. huxleyi
Temperature and nutrient supply are key factors that control phytoplankton ecophysiology, but their role is commonly investigated in isolation. Their combined effect on resource allocation, photosynthetic strategy, and metabolism remains poorly understood. To characterize the photosynthetic strategy and resource allocation under different conditions, we analyzed the responses of a marine cyanobacterium (
Synechococcus PCC7002) to multiple combinations of temperature and nutrient supply. We measured the abundance of proteins involved in the dark (RuBis CO, rbcL) and light (Photosystem II, psbA) photosynthetic reactions, the content of chlorophyll a, carbon and nitrogen, and the rates of photosynthesis, respiration, and growth. We found that rbcL and psbA abundance increased with nutrient supply, whereas a temperature‐induced increase in psbA occurred only in nutrient‐replete treatments. Low temperature and abundant nutrients caused increased RuBis COabundance, a pattern we observed also in natural phytoplankton assemblages across a wide latitudinal range. Photosynthesis and respiration increased with temperature only under nutrient‐sufficient conditions. These results suggest that nutrient supply exerts a stronger effect than temperature upon both photosynthetic protein abundance and metabolic rates in Synechococcussp. and that the temperature effect on photosynthetic physiology and metabolism is nutrient dependent. The preferential resource allocation into the light instead of the dark reactions of photosynthesis as temperature rises is likely related to the different temperature dependence of dark‐reaction enzymatic rates versus photochemistry. These findings contribute to our understanding of the strategies for photosynthetic energy allocation in phytoplankton inhabiting contrasting environments.
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Skeletonema, three forms of genes encoding high‐affinity nitrate transporters ( ) were newly identified from transcriptomes generated as part of the marine microbial eukaryote transcriptome sequencing project. To examine the expression of each form of NRT2 under different nitrogen environments, laboratory experiments were conducted under nitrate‐sufficient, ammonium‐sufficient, and nitrate‐limited conditions using three ecologically important NRT2 Skeletonemaspecies: S. dohrnii, S. menzelii,and S. marinoi. Primers were developed for each form and species and Q‐ NRT2 RT‐ PCRwas performed. For each form, the three NRT2 Skeletonemaspecies had similar transcriptional patterns. The transcript levels of were significantly elevated under nitrogen‐limited conditions, but strongly repressed in the presence of ammonium. The transcript levels of NRT2:1 were also repressed by ammonium, but increased 5‐ to 10‐fold under nitrate‐sufficient and nitrogen‐limited conditions. Finally, the transcript levels of NRT2:2 did not vary significantly under various nitrogen conditions, and behaved more like a constitutively expressed gene. Based on the observed transcript variation among NRT2:3 forms, we propose a revised model describing nitrate uptake kinetics regulated by multiple forms of nitrate transporter genes in response to various nitrogen conditions in NRT2 Skeletonema. The differential transcriptional responses among species suggest that species‐specific adaptive strategies exist within this genus to cope with environmental changes. NRT2
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Alternative polyadenylation (
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