Adjusting the Circadian Clock

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Published on: June 3, 2014

As highlighted in Lisa’s excellent weekly Arabidopsis Research Round-up two weeks ago, a paper on the feedback loop mechanisms that give the circadian clock flexibility was recently published in New Phytologist Early View (DOI: 10.1111/nph.12853Open Access) by GARNet 2014 speaker Andrew Millar. Here first author Laura Dixon, post-doctoral researcher in flowering regulation in the Department of Crop Genetics at the John Innes Centre, explains the research.

Dixon May2014
Arabidopsis thaliana (left) and single celled green alga Ostreococcus tauri

The circadian clock is an innate time-keeping mechanism found in most organisms, and has a period of about 24 hours. The circadian rhythm syncs to the environment as the clock mechanism adjusts to long or short photoperiods, or environmental summer and winter, and so co-ordinates many biological processes with respect to time of day and season. How quickly these adjustments can occur varies between species, and is believed to be a property of how many interlocking feedback loops the circadian clock mechanism is comprised of.

To empirically test the idea that clock flexibility is linked to the number of interlocking feedback loops within the circadian clock mechanism, we compared the fairly complex Arabidopsis thaliana clock to the very reduced clock of the smallest free-living eukaryote, unicellular green alga Ostreococcus tauri. We use A. thaliana as a plant model as it is a simple system relative to often very complex crop species. Many crop species are polyploid and so have very complicated signalling pathways; Arabidopsis is simpler but still contains complex regulation which can inform crop research. The Arabidopsis clock is a network of interlocking feedback loops. Groups of gene families encode clock components and at least 10 photoreceptor proteins.

We switched photoperiod conditions directly between short day and long day and observed what happened in the two systems. In combination with network analysis through mathematical modelling of the proposed possible clock structures, we showed that flexibility of entrainment to environmental conditions is a property of both the number of interlocking loops and the number of light inputs to the clock mechanism. Our research highlights one of the mechanisms through which circadian clock transcriptional and translational loops are flexible and adaptable in response to environmental conditions.

Images: A. thaliana from GARNet; TEM of Ostreococcus from Eikrem and Throndsen University of Oslo

Photosynthesis for fresh water

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Published on: February 10, 2014

Annegret Honsbein is a post-doc in Anna Amtmann‘s lab at the University of Glasgow. As she explains in this guest post, she is working on an EPSRC project that hopes to harness the power of photosynthesis to desalinate sea water. 

Water covers more than 70% of Earth’s surface but less than 2% of it is available as freshwater. Many of the driest regions of our planet are close to the sea but irrigating fields with seawater – even if diluted – leads to build-up of salt in the soil to levels toxic to all common food crops. Current desalination technologies, such as membrane-based reverse osmosis, are successfully used in large-scale desalination plants, but they are expensive and energy inefficient.

desalinationOur multi-disciplinary EPSRC-funded project takes a synthetic biology approach to the development of an innovative desalination technology based on biological processes. We are a team of biologists and engineers from the Universities of Glasgow, Sheffield, Newcastle, Robert Gordon University at Aberdeen and Imperial College London, led by Dr. Anna Amtmann from Glasgow University.

Our idea is solar energy-fuelled desalination – with a twist. Instead of using solar panels we intend to let photosynthetic microorganisms desalinate the sea water. Cyanobacteria are ideal candidates, and we are currently working with two strains that are naturally able to adapt to a wide range of salt concentrations from fresh to sea water.

In principle, salt is toxic to all living cells, which is why most living systems have developed means to actively export sodium. In some cyanobacteria species that grow to very high densities, this ability means they actually form a low-salt reservoir within their saline environment.

We intend to use this low-salt reservoir as ion exchanger to extract the salt from the surrounding seawater. We aim to engineer cyanobacteria so we can switch off the endogenous salt export mechanism towards the end of their growth cycle, and activate a synthetic intracellular sodium accumulation unit. This synthetic unit will be assembled from membrane transport proteins evolved by different organisms to import sodium and chloride ions.

Our team’s engineers are developing techniques to manipulate the surface properties of the cyanobacteria and effectively separate the ‘salty’ cells from the desalinated water before they die, preventing release of the accumulated salt back into the ‘fresh’ water.

The final stage of the project will be to build a model version of the actual plant that could house our photosynthesis-driven bio-desalination process.

This work is published in: Jaime M. Amezaga, Anna Amtmann, Catherine A. Biggs, Tom Bond, Catherine J. Gandy, Annegret Honsbein, Esther Karunakaran, Linda Lawton, Mary Ann Madsen, Konstantinos Minas and Michael R. Templeton (2014) Biodesalination: A Case Study for Applications of Photosynthetic Bacteria in Water Treatment. Plant Physiology 164: 1661-1676; doi: http:/​/​dx.​doi.​org/​10.​1104/​pp.​113.​233973.

Image c/o Annegret Honsbein.

Staying together: green beginnings

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Published on: November 5, 2013
This seaweed, Ulva linza, would only exist as undifferentiated cells if not for bacterial signals

The second of our series of blog posts Celebrating Basic Plant Science is written by Juliet Coates, Lecturer in Molecular Genetics at the University of Birmingham.

Living organisms can be categorised in a number of ways, but one very obvious “either/or” distinction is between organisms that are made up of a single cell – unicellular organisms – and those that are many-celled, or multicellular.

The multicellular state arose many times during evolution: animals, plants, algae, amoebae, fungi and bacteria can all be multicellular. Multicellular organisms completely underpin life on Earth as we know it today – and they all must have evolved from single-celled ancestors. We understand a little of why they might have done so, as being multicellular gives a number of competitive advantages: increased size and improved nutrient collection being just two. Yet how multicellular organisms came to be is a key biological problem that is still largely unanswered.

I am a plant scientist, so I am particularly interested in the origins of multicellular green things: plants and algae. Without becoming multicellular, plants would never have colonised the land, and the evolution of multicellular plants and algae was key in shaping our climate, our ecosystems and our oxygen-rich atmosphere. How green multicellularity arose seems to me to be a really fundamental thing to understand, but it is a little-addressed question. Here I’ll give an overview of the important findings to date about the evolution of multicellularity.



Thinking about phytoplankton

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Published on: October 16, 2012
H. akashiwo on the right, with predator Favella sp.

I’m aware phytoplankton are not usual subjects for plant science research, but these small algae are quite plant-like, in general – although they don’t have organs to complicate things. Like plants, they photosynthesize and are able to respond to their environment. Importantly, unlike plants, phytoplankton are mobile, hence the name which in Greek means ‘drifting plants’. Being extremely tiny ‘plants’, phytoplankton present an excellent opportunity for plant scientists to consider synthetic biology, which seems more feasible on a cell-scale rather than an entire plant. The super-theme of the FP7 2013 funding call was ‘The Oceans of Tomorrow,’ and while that call closes in a few short months, synthetic biology, water security and bio-sensors are important research themes which are here to stay.

Highlighted article: Elizabeth L. Harvey and Susanne Menden-Deuer (2012) Predator-Induced Fleeing Behaviors in Phytoplankton: A New Mechanism for Harmful Algal Bloom Formation? PLoS ONE 7(9): e46438. doi:10.1371/journal.pone.0046438

This research focuses on toxic phytoplankton Heterosigma akashiwo, a known cause of harmful algal blooms (HABs; for a fairly recent review of HABs and their effects on human health, see Backer and McGillicuddy Jr., 2006). (more…)

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