Submitted to: Plant Biotechnology Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/25/2011
Publication Date: 8/13/2011
Publication URL: http://handle.nal.usda.gov/10113/54533
Citation: Adams, J.P., Adeli, A., Hsu, C., Harkness, R.L., Page, G.P., Depamphilis, C.W., Schultz, E.B., Yuceer, C. 2011. Plant-based FRET biosensor discriminates enviornmental zinc levels. Plant Biotechnology Journal. 10:207-216. Interpretive Summary: Zinc (Zn) levels can build up in the environment and adversely impact both animal and plant communities. Some extreme contaminated sites are easily identified by biota mortality or by biota exhibiting classic contamination signs (e.g. foliar chlorosis, necrosis and loss of turgor). Nonpoint sources causing gradual metal accumulation in soil and the food chain or heterogeneity of the metal distribution can pose a larger threat because of inabilities to diagnose contamination. Realization of threats from Zn accumulation or other similar metals (i.e. heavy metals that are group IIB transition metals on the periodic table), such as cadmium, is vital for the protection of food production and soil management. In current agricultural practices, soil sampling is a vital, widely used tool for monitoring and managing soil. While this enables identification of heavy metals, such tests are static in time and are costly across large land areas. Also, soil leaching can lead to metal movement beyond sampled areas causing sampling to miss areas of contamination. Plants have many benefits for use in this method. One benefit is that they produce large amounts of biomass that provide adequate amounts of tissue for sampling. Also, they are stationary and can provide large, expansive root systems allowing for nutrient acquisition from a broad area of soil. While plants, and especially tree species, can provide large sinks for various substrates, sampling tissues would still incur costs similar to soil nutrient analysis. A real-time method is potentially feasible using currently available fluorescent proteins (FPs) and genetic modification techniques. This fluorescent resonance energy transfer (FRET) provides a means for substrate monitoring. Real-time monitoring has been absent in proposed soil health measurement methods including fungal produced crystal counts and plant phytochelatin counts. However, current FRET technologies have been shown to potentially fill this gap; though, such a technique has not been implemented in plant species for the intent of soil.
Technical Abstract: Heavy metal accumulation in the environment poses great risks to flora and fauna. However, monitoring sites prone to accumulation poses scale and economic challenges. In this study, we present and test a method for monitoring these sites using fluorescent resonance energy transfer (FRET) change in response to zinc (Zn) accumulation in plants as a proxy for environmental health. We modified a plant Zn transport protein by adding flanking fluorescent proteins (FPs) and deploying the construct into two different species. In Arabidopsis thaliana, FRET was monitored by a confocal microscope and had a 1.4-fold increase in intensity as the metal concentration increased. This led to a 16.7% overall error-rate when discriminating between a control (1 lM Zn) and high (10 mM Zn) treatment after 96 h. The second host plant (Populus tremula x Populu salba) also had greater FRET values (1.3-fold increase) when exposed to the higher concentration of Zn, while overall error-rates were greater at 22.4%. These results indicate that as plants accumulate Zn, protein conformational changes occur in response to Zn causing differing interaction between FPs. This results in greater FRET values when exposed to greater amounts of Zn and monitored with appropriate light sources and filters. We also demonstrate how this construct can be moved into different host plants effectively including one tree species. This chimeric protein potentially offers a method for monitoring large areas of land for Zn accumulation, is transferable among species, and could be modified to monitor other specific heavy metals that pose environmental risks.