Team:FAFU-CHINA/Experiments
Module 1: Phyto-route
Module 2: Metal-trap
Module 3: Safeguard
Phytoremediation is the use of plants and associated soil microbes to reduce the concentrations or toxic effects of heavy metals in the environments. It is a relatively recent technology and is perceived as cost-effective, efficient, novel, eco-friendly, and solar-driven technology with good public acceptance. In our project, we have selected hyperaccumulator- Sedum alfredii Hance to uptake heavy metals in the metalliferous soil and increased ability of plants expressing the bacterial enzyme ACC deaminase(BB0J_00链接到part页面) to accumulate heavy metals.
Overview
Hyperaccumulator was coined for plants that, differently from the excluder plants, actively take up exceedingly large amounts of one or more heavy metals from the soil. Moreover, the heavy metals are not retained in the roots but are translocated to the shoot and accumulated in aboveground organs（链接到生测实验部分）, especially leaves and stem at concentrations 100–1000-fold higher than those found in non-hyperaccumulating species.
The major processes involved in hyperaccumulation of trace metals from the soil to the shoots by hyperaccumulators include: (a) bioactivation of metals in the rhizosphere through root–microbe interaction; (b) enhanced uptake by metal transporters in the plasma membranes; (c) detoxification of metals by distributing to the apoplasts like binding to cell walls and chelation of metals in the cytoplasm with various ligands, such as phytochelatins, metallothioneins, metal-binding proteins; (d) sequestration of metals into the vacuole by tonoplast-located transporters.
Fig. 1 Hyperaccumulator- Sedum alfredii Hance grown in the growth chamber with a 16/8 h (22/18 ℃) day/night regimes at 120 molm-2 s-1 irradiation during our phyto-experiment.(Picture by FAFU-CHINA team 2017).
Ethylene is a gaseous plant growth hormone produced endogenously by almost all plants. Apart from being a plant growth regulator, ethylene has also been established as a stress hormone. Under stress conditions like those generated by salinity, drought, waterlogging, heavy metals（链接到Bacground） and pathogenicity, the endogenous production of ethylene is accelerated substantially which adversely affects the root growth(链接到拟南芥lab部分) and consequently the growth of the plant as a whole.
1-aminocyclopropane-1-carboxylate (ACC) deaminase(链接ACCD part部分), which regulates ethylene production by metabolizing ACC (an immediate precursor of ethylene biosynthesis in higher plants) into α-ketobutyrate and ammonia，simultaneously enhances plant growth and biomass by P solubilization and uptake particularly under stress condition by heavy metals.
Fig. 2 Plants growth promoting parameters. Abbreviations: indole-3-acetic acid (IAA), methionine-S-adenosylmethionine (SAM), 1-aminocyclopropane-1-carboxylate (ACC).
Reference
Yang, X., Feng, Y., He, Z., & Stoffella, P. J. (2005). Molecular mechanisms of heavy metal hyperaccumulation and phytoremediation, 18, 339–353. https://doi.org/10.1016/j.jtemb.2005.02.007
Ma, Y., Prasad, M. N. V, Rajkumar, M., & Freitas, H. (2011). Plant growth promoting rhizobacteria and endophytes accelerate phytoremediation of metalliferous soils Phytoremediation Bioremediation Rhizoremediation, 29, 248–258. https://doi.org/10.1016/j.biotechadv.2010.12.001
Saleem, M., Arshad, M., Hussain, S., & Saeed, A. (2007). Perspective of plant growth promoting rhizobacteria ( PGPR ) containing ACC deaminase in stress agriculture, 635–648. https://doi.org/10.1007/s10295-007-0240-6
Zhang, Y., Zhao, L., Wang, Y., Yang, B., & Chen, S. (2008). Chemosphere Enhancement of heavy metal accumulation by tissue specific co-expression of iaaM and ACC deaminase genes in plants, 72, 564–571. https://doi.org/10.1016/j.chemosphere.2008.03.043
Fig 1 Toggle switch, a mechanism that is triggered if a human operator becomes incapacitated, allows cells to live as long as an operator compound (anhydrotetracycline, ATc) is present.
Biochtainment systems that couple enviromental sensing with circuit-based control of cell viability could be used to prevent escape of genetically modified microbes into the enviroment. In order to guarantee our chassis’ safety of the application in reality , we have taken a robust and significant strategy, dubbed ‘Toggle Switch’(BB0J_00part页面), based on a circuit which the LacI and TetR transcription factors are reciprocally repressive.
Overview
For Human Practice-Discussion Panel(链接到HP的部分), we have come up with a common question to President Shi that “If our project needs to be applied in practice, what will be the specific operation processes? And of what aspects shall we be conscious? ”. It is a essential reminder of his answers tha there is the need for constant care. We decided to customize a ‘kill switch’ as a safeguard for our project, simultaneously harbors a neutral statet that allows billions of microbes to happily thrive and avoid unexpectedly escaping of GEMs into the enviroment and transferring of non-natural plasmid DNA to existing soil bacteria. ‘Toggle Switch’, based on a circuit which the LacI and TetR transcription factors are reciprocally repressive, but in which the expression off TetR is favoured owing to modifications in the strength of the ribosommal binding sites of the two transcription factors. Inhibition of TetR expression by anhydrotetracycline(ATc), a compound that is not normally found in nature, is necessary of expression of LacI. LacI directly inhibits expression of a lethal toxin or indirectly prevents inhibition of the expression of our target genes. Removal of ATc from the enviroment activates the expression of TetR, which leads to cell death. For more information about lab, please click here.(链接到lab页面）
Reference
Haynes, K. A. (2016). Synthetic biology: Building genetic containment. Nature Publishing Group, 12(2), 55–56. https://doi.org/10.1038/nchembio.2004
Osório, J. (2015). Genetic kill switches — a matter of life or death. Nature Publishing Group, 1979(December), 2015. https://doi.org/10.1038/nrg.2015.29
Chan, C. T. Y., Lee, J. W., Cameron, D. E., Bashor, C. J., & Collins, J. J. (2015). for bacterial containment. Nature Chemical Biology, (December), 1–7. https://doi.org/10.1038/nchembio.1979
