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Monica Orellana

Research Scientist/Engineer - Principal & Principal Oceanographer





Department Affiliation

Polar Science Center


B.S. Biology, Concepcion (Chile), 1980

M.S. Biological Oceanography, University of Washington, 1985

Ph. D. Biological Oceanography, University of Washington, 1990


2000-present and while at APL-UW

Diatom acclimation to elevated CO2 via cAMP signalling and coordinated gene expression

Hennon, G.M.M., J. Ashworth, R.D. Groussman, C. Berthiaume, R.L. Morales, N.S. Baliga, M.V. Orellana, and E.V. Armbrust, "Diatom acclimation to elevated CO2 via cAMP signalling and coordinated gene expression," Nat. Clim. Change, 5, 761-765, doi:10.1038/nclimate2683, 2015.

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15 Jun 2015

Diatoms are responsible for ~40% of marine primary productivity, fuelling the oceanic carbon cycle and contributing to natural carbon sequestration in the deep ocean. Diatoms rely on energetically expensive carbon concentrating mechanisms (CCMs) to fix carbon efficiently at modern levels of CO2. How diatoms may respond over the short and long term to rising atmospheric CO2 remains an open question. Here we use nitrate-limited chemostats to show that the model diatom Thalassiosira pseudonana rapidly responds to increasing CO2 by differentially expressing gene clusters that regulate transcription and chromosome folding, and subsequently reduces transcription of photosynthesis and respiration gene clusters under steady-state elevated CO2. These results suggest that exposure to elevated CO2 first causes a shift in regulation, and then a metabolic rearrangement. Genes in one CO2-responsive cluster included CCM and photorespiration genes that share a putative cAMP-responsive cis-regulatory sequence, implying these genes are co-regulated in response to CO2, with cAMP as an intermediate messenger. We verified cAMP-induced downregulation of CCM gene δ-CA3 in nutrient-replete diatom cultures by inhibiting the hydrolysis of cAMP. These results indicate an important role for cAMP in downregulating CCM and photorespiration genes under elevated CO2 and provide insights into mechanisms of diatom acclimation in response to climate change.

Genome-wide diel growth state transitions in the diatom Thalassiosira pseudonana

Ashworth, J., S. Coesel, A. Lee, E.V. Armbrust, M.V. Orellana, and N.S. Baliga, "Genome-wide diel growth state transitions in the diatom Thalassiosira pseudonana," Proc. Nat. Acad. Sci. USA, 110, 7518-7523, doi:10.1073/pnas.1300962110, 2013.

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30 Apr 2013

Marine diatoms are important primary producers that thrive in diverse and dynamic environments. They do so, in theory, by sensing changing conditions and adapting their physiology accordingly. Using the model species Thalassiosira pseudonana, we conducted a detailed physiological and transcriptomic survey to measure the recurrent transcriptional changes that characterize typical diatom growth in batch culture. Roughly 40% of the transcriptome varied significantly and recurrently, reflecting large, reproducible cell-state transitions between four principal states: (i) "dawn," following 12 h of darkness; (ii) "dusk," following 12 h of light; (iii) exponential growth and nutrient repletion; and (iv) stationary phase and nutrient depletion. Increases in expression of thousands of genes at the end of the reoccurring dark periods (dawn), including those involved in photosynthesis (e.g., ribulose-1,5-bisphosphate carboxylase oxygenase genes rbcS and rbcL), imply large-scale anticipatory circadian mechanisms at the level of gene regulation. Repeated shifts in the transcript levels of hundreds of genes encoding sensory, signaling, and regulatory functions accompanied the four cell-state transitions, providing a preliminary map of the highly coordinated gene regulatory program under varying conditions. Several putative light sensing and signaling proteins were associated with recurrent diel transitions, suggesting that these genes may be involved in light-sensitive and circadian regulation of cell state. These results begin to explain, in comprehensive detail, how the diatom gene regulatory program operates under varying environmental conditions. Detailed knowledge of this dynamic molecular process will be invaluable for new hypothesis generation and the interpretation of genetic, environmental, and metatranscriptomic data from field studies.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center