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Team:Purdue/Oxygen Sequestration to Inhibit Photorespiration in C3 Plants
From 2010.igem.org
Contents |
The problem
Photorespiration is an unwanted chemical process that occurs in C3 plants that wastes ATP and organic nitrogen. While many species have evolved to avoid photorespiration (C4 and CAM plants), attempts to transfer these methods to C3 plants have been unsuccessful due to the drastic physiological differences between species. Photorespiration occurs when O2 concentrations increase relative to CO2. In relatively dry conditions, the stomata of plants close to preserve moisture. Unfortunately, these stomata are used for the exchange of atmospheric CO2 with photosynthetically-derived O2. When the stomata close, the light-independent reactions of photosynthesis, notably the Calvin cycle, continue. The Calvin cycle's purpose is to fix inorganic carbon (CO2) to generate a three-carbon sugar (G3P). The key enzyme in the carbon-fixation process is RuBisCO. Normally, RuBisCO directly fixes the CO2 to RuBP (an intermediate of the Calvin cycle) to produce G3P. However, RuBisCO also has a significant affinity for O2, and can oxygenate RuBP instead. This generates less G3P and produces a toxic intermediate. Eliminating this toxic intermediate requires 1 ATP and causes the formation of NH3, which diffuses out of the plant.
The solution
Hemoproteins (such as hemoglobin and leghemoglobin) are capable of binding O2 with various affinities. By combining a hemoprotein with a sequence that codes for protein import into the stroma of the chloroplast (a sequence found in the RuBisCO protein), excess oxygen produced during photosynthesis can be sequestered. In theory, this would reduce oxygen concentrations and inhibit photorespiration. A promoter for high dissolved oxygen concentrations could increase production of the hemoprotein during times that photorespiration is likely to occur in excess.
Resources
Photorespiration and Calvin cycle review
[http://khanexercises.appspot.com/video?v=EQvTEFCANTM Khan Academy video lecture]
Potentially useful articles
[http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.arplant.043008.091948?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dncbi.nlm.nih.gov Processes Relevant to Photorespiration] - Addresses metabolic pathways associated to photorespriation
[http://dx.doi.org/10.1016/j.copbio.2005.02.001 Great article on plant response to abiotic stress] - Discusses applications of genetic engineering to improving stress tolerance
[http://www.uni-tuebingen.de/plantphys/AFGN/atgenex.htm Arabidopsis study on gene expression under a variety of conditions] - Of particular interest is the gene expression during oxidative and heat stress.
[http://www3.interscience.wiley.com/cgi-bin/fulltext/121356215/HTMLSTART Changes in gene expression in Arabidopsis due to available oxygen]
Brainstorming Page: Purdue Oxygen Sequestration Brainstorming & Thoughts
Purdue-Home: Team:Purdue
Discussion
I've found a book on abiotic stress response that had a chapter based on the Arabidopsis study mentioned above. The responses to oxidative stress had more to do with [http://wikipedia.org/Paraquat Paraquat], an herbicide that interferes with electron transfer. The response to heat stress may be more important, and given what we know about when photorespiration occurs, that's probably a more reasonable pursuit. I'd be somewhat surprised if genes specific to high oxygen concentrations exist. [http://www.ncbi.nlm.nih.gov/gene/827496 Arabidopsis thaliana heat-shock factor 1] seems like a good candidate. --Jmason
Also, the activity of heat-shock transcription factors seems to be conserved among all eukaryotes. --Jmason
Searching 'oxygen' in the [http://www.partsregistry.org parts registry] gives a number of parts related to oxygen sensitive detection, binding, and regulation. It is a good idea to look at these to determine if there is something here that would accomodate our ideas. --Skearney
<partinfo>BBa_K258005</partinfo>
Here are some files on Algal photorespiration, algal biofuels, and another on biofuels. --Lgyoung
