Project description:Diel proteomes of Trichodesmium colonies sampled from the field on March 10, 2018 from the Eastern subtropical Atlantic at 65 22.420W 17 0.284 N. These proteomes inform a broad study of diel proteome oscillations in Trichodesmium that support simultaneous photosynthesis and nitrogen fixation during the day.
Project description:Investigation of whole genome gene expression level changes in two strains of the cyanobacteria Atelocyanobacterium thalasaa (UCYN-A) from environmental samples. The diel gene expression analyzed in this study is further described in Muñoz-Marin, M., I. N. Shilova, T. Shi, H. Farnelid & J. P. Zehr. 2017. Unicellular cyanobacterial symbiosis facilitates aerobic nitrogen fixation. Science (to be submitted).
Project description:The photosynthetic model marine diatom Phaeodactylum tricornutum was cultured under conditions varying nitrogen content and availability, or varying iron concentrations over diel cycles to elicit shifts in the proteome and phosphoproteome. For the nitrogen experiments, cells were grown to mid-exponential phase on ammonium (880 uM), collected by centrifugation and resuspended in N-free media for 2 hrs, and spiked with nitrate (150 uM) for 90 min. Cells were again collected by centrifugation, washed in N-free media, and resuspended in experimental treatments with no nitrogen (N-) and a nitrogen source (300 uM) provided as ammonium, nitrite, or nitrate. Each experimental treatment was sampled after 15 min, 45 min, and 18 hr. For iron experiments, steady-state axenic cultures were maintained under a diel cycle of 12h light: 12h darkness and at three different concentrations of Fe' (Fe' is the sum of all Fe species not complexed to EDTA): a low concentration (20 pM Fe'), intermediate concentration (40 pM Fe') and at Fe-replete levels (400 pM Fe'). Samples were taken every four hours.
Project description:Although N2 fixation can occur in free-living cyanobacteria, the unicellular endosymbiotic cyanobacterium Candidatus Atelocyanobacterium thalassa (UCYN-A) is considered to be a dominant N2-fixing species in marine ecosystems. Four UCYN-A sublineages are known from partial nitrogenase (nifH) gene sequences. However, few studies have investigated their habitat preferences and regulation by their respective hosts in open-ocean versus coastal environments. Here, we compared UCYN-A transcriptomes from oligotrophic open-ocean versus nutrient-rich coastal waters. UCYN-A1 metabolism was more impacted by habitat changes than UCYN-A2. However, across habitats and sublineages genes for nitrogen fixation and energy production were highly transcribed. Curiously these genes, critical to the symbiosis for the exchange of fixed nitrogen for fixed carbon, maintained the same schedule of diel expression across habitats and UCYN-A sublineages, including UCYN-A3 in the open-ocean transcriptomes. Our results undersore the importance of nitrogen fixation in UCYN-A symbioses across habitats, with consequences for community interaction and global biogeochemical cycles.
Project description:Biological rhythms in response to both endogenous (circadian) and exogenous (e.g. diel) cycles, with a period of ~24 hours, are a prominent feature of many living systems. In green algal species, knowledge on the extent of diel rhythmicity of genome wide gene expression, its evolution, and its cis-regulatory mechanism is limited. In this study, we identified cyclically expressed genes under diel conditions in Chlamydomonas reinhardtii and found that ~50% of the 17,114 annotated genes exhibited cyclic expression. The cyclic expression patterns indicate a clear succession of biological processes during the course of a day. Among 237 functional categories enriched in cyclically expressed genes, >90% were phase-specific, including photosynthesis, cell division and motility processes. By contrasting cyclic expression between C. reinhardtii and Arabidopsis thaliana putative orthologs, we found significant but weak conservation in cyclic gene expression patterns. On the other hand, within C. reinhardtii cyclic expression was preferentially maintained, particularly amongst older duplicates, and the evolution of phase between paralogs is limited to relatively minor shifts in time. Finally, to better understand the cis regulatory basis of diel expression, putative cis-regulatory elements were identified that could predict the expression phase of a subset of the cyclic transcriptome. Our findings demonstrate both the prevalence of as well as the complex regulatory circuitry required to control cyclic expression in a green algal model, highlighting the need to consider diel expression in studying algal molecular networks and in future biotechnological applications.
Project description:Biological rhythms in response to both endogenous (circadian) and exogenous (e.g. diel) cycles, with a period of ~24 hours, are a prominent feature of many living systems. In green algal species, knowledge on the extent of diel rhythmicity of genome wide gene expression, its evolution, and its cis-regulatory mechanism is limited. In this study, we identified cyclically expressed genes under diel conditions in Chlamydomonas reinhardtii and found that ~50% of the 17,114 annotated genes exhibited cyclic expression. The cyclic expression patterns indicate a clear succession of biological processes during the course of a day. Among 237 functional categories enriched in cyclically expressed genes, >90% were phase-specific, including photosynthesis, cell division and motility processes. By contrasting cyclic expression between C. reinhardtii and Arabidopsis thaliana putative orthologs, we found significant but weak conservation in cyclic gene expression patterns. On the other hand, within C. reinhardtii cyclic expression was preferentially maintained, particularly amongst older duplicates, and the evolution of phase between paralogs is limited to relatively minor shifts in time. Finally, to better understand the cis regulatory basis of diel expression, putative cis-regulatory elements were identified that could predict the expression phase of a subset of the cyclic transcriptome. Our findings demonstrate both the prevalence of as well as the complex regulatory circuitry required to control cyclic expression in a green algal model, highlighting the need to consider diel expression in studying algal molecular networks and in future biotechnological applications. Total RNA sequences extracted every 3 hours between ZT (Zeitgeber Time, hours since last doawn) 0 and ZT21 from two biological replicates of C. reinhardtiis dw15.1
Project description:Iron (Fe) is an important growth limiting factor for diatoms and its availability is further restricted by changes in the carbonate chemistry of the water. We investigated the physiological attributes and transcriptional profiles of the diatom Thalassiosira pseudonana grown on a day:night cycle under different CO2/pH and iron concentrations, that in combination generated available iron (Fe’) concentrations of 1160, 233, 58 and 12 pM. We found the light-dark conditions to be the main driver of transcriptional patterns, followed by Fe’ concentration and CO2 availability, respectively. At the highest Fe’ (1160 pM), 55% of the transcribed genes were differentially expressed between day and night, whereas at the lowest Fe’ (12 pM), only 28% of the transcribed genes displayed comparable patterns. While Fe limitation disrupts the diel transcriptional patterns for genes in most central metabolism pathways, the diel periodicity of light- signaling molecules and glycolytic genes, was relatively robust in response to reduced Fe’. Moreover, we identified a non-canonical splicing of transcripts encoding triose-phosphate isomerase, a key-enzyme of glycolysis, generating transcript isoforms that would encode proteins with and without an active site. Transcripts that encoded an active enzyme maintained a diel pattern at low Fe’, while transcripts that encoded the non-active enzyme lost the diel pattern. This work illustrates the interplay between nutrient limitation and transcriptional regulation over the diel cycle. Considering that future ocean conditions will reduce the availability of Fe in many parts of the oceans, our work identifies some of the regulatory mechanisms that may shape future ecological communities.