Team:HKUST-Rice/Description
Project
Overview
Nitrogen (N), phosphorus (P) and potassium (K) are three plant macronutrients, and deficiencies in any of these can lead to plant diseases. By creating a biological sensor that can quickly provide soil status to plant owners, we can prevent plant diseases due to the lack of nutrients. In view of this, our team constructed a biological sensor in E. coli, which can detect NPK levels in the surrounding environment and give responses in the form of colors. In addition, we characterized the effects of a dual output system, in contrast to a single output system, in order to anticipate the expression of multiple outputs in a single system.
Nitrate Sensor
PyeaR is normally cross-regulated by the Nar two-component regulatory system (Nohno et al., 1989; Lin et al., 2007) and NsrR, a regulatory protein. When there is nitrate and nitrite, it will be converted into nitric oxide. The nitric oxide will bind to NsrR and relieve the repression on the PyeaR. As a result, any genes that are downstream of the PyeaR promoter will be expressed.
Figure 3. Construct for nitrate sensing. PyeaR with GFP generator.
Phosphate Sensor
PphoA and PphoBR promoters are cross-regulated by phoB and phoR and repressed under high phosphate concentrations (Hsieh & Wanner, 2010). PhoR behaves as an activator as well as an inactivator for PhoB. When phosphate is limited, PhoR will phosphorylate PhoB and the phosphorylated PhoB will directly activate the PphoA and PphoBR promoters.
Figure 2. Phosphate sensor constructs. (a) PphoA with GFP generator and (b) PphoBR with GFP generator.
Potassium Sensor
kdpFABC transporter is a high affinity K+ uptake system (Siebers & Altendorf, 1988). The promoter upstream of kdpFABC operon,PkdpF, works under low K+ concentrations (Polarek et al., 1992; Walderhaug et al., 1992). The goal is to characterize PkdpF and build a device which is able to sense different concentrations of K+ and express different levels of GFP accordingly.
Figure 1. K+ sensing construct with reporter.
Parallel Sensors
In order to characterize the output difference between a single expression system and co-expression system from one vector, we built two inducible systems and compared the dose response of each of the individual system in a single construct plasmid to that of a double construcst plasmid. Fluorescence was used as the readout.
ParaBAD
We build one of the inducible system using ParaBAD. However discoved that there are different opinions on the mode of response of this widely used promoter. As such we decided to investigate on this promoter.
Figure 4. Brief diagrams of single and double constructs.
References
Nohno, T., Noji, S., Taniguchi, S., & Saito, T. (1989). The narX and narL genes encoding the nitrate-sensing regulators of Escherichia coli are homologous to a family of prokaryotic two-component regulatory genes. Nucleic acids research,17(8), 2947-2957.
Lin, H. Y., Bledsoe, P. J., & Stewart, V. (2007). Activation of yeaR-yoaG operon transcription by the nitrate-responsive regulator NarL is independent of oxygen-responsive regulator Fnr in Escherichia coli K-12. Journal of bacteriology, 189(21), 7539-7548.
Hsieh, Y. J., & Wanner, B. L. (2010). Global regulation by the seven-component P i signaling system. Current opinion in microbiology, 13(2), 198-203.
Siebers, A. and Altendorf, K. (1988). The K+-translocating Kdp-ATPase from Escherichia coli. European Journal of Biochemistry, 178, 131–140.
Walderhaug, M. O., Polarek, J. W., Voelkner, P., Daniel, J. M., Hesse, J. E., Altendorf, K., & Epstein, W. (1992). KdpD and KdpE, proteins that control expression of the kdpABC operon, are members of the two-component sensor-effector class of regulators. Journal of Bacteriology, 174(7), 2152–2159.
Green, A.A., Silver, P.A., Collins, J.J., & Yin, P. (2014). Toehold Switches: De-Novo-Designed Regulators of Gene Expression. Cell, 157(4), 925-935.