Modify Azolla to hyper accumulate silver - Your Published Bio Team Output
**Pre-Project**As a starting point, the overall objective of modifying Azolla, a fern that can fix atmospheric nitrogen, to hyper accumulate silver could be to develop a low-cost and environmentally friendly method for the remediation of silver-contaminated soil and water bodies.
One endogenous pathway that might be useful to modify is the metal chelator biosynthesis pathway in Azolla. Metal chelators are compounds that can bind to metal ions, preventing them from damaging cellular structures. By upregulating the metal chelator biosynthesis pathway, Azolla could produce more metal chelators that could bind with silver ions and help to reduce the toxicity of silver in the fern.
Now, for the pathway from a different species that could be imported, researchers could look at the silver uptake pathway in Arabidopsis halleri, a plant species that has been shown to hyper accumulate cadmium and zinc. It's hypothesized that this species may use symplastic transport (cell-to-cell transport through plasmodesmata) to move metals from the root to the shoot. By importing this pathway into Azolla, researchers could increase the transport of silver ions from the root to the shoot, thereby improving the fern's ability to hyper accumulate silver.
To achieve the desired result, researchers could invest in genetic engineering technologies to modify Azolla's endogenous metal chelator biosynthesis pathway and to import Arabidopsis halleri's silver uptake pathway. The genes responsible for the production of metal chelators in Azolla could be overexpressed or introduced from other sources to enhance the fern's ability to bind to and reduce the toxicity of silver. Similarly, the genes contributing to the symplastic transport of silver ions in Arabidopsis halleri could be introduced into Azolla to improve its ability to transport silver ions from the root to the shoot.
In terms of the selection of the subspecies or variety of Azolla, the species Azolla pinnata has been reported to exhibit high heavy metal tolerance and uptake. This subspecies could be a potential candidate for genetic engineering since it already exhibits some of the desirable traits required for the remediation of contaminated soils and water bodies.
In summary, modifying Azolla to hyper accumulate silver would require the modification of its endogenous metal chelator biosynthesis pathway, as well as the import of the silver uptake pathway from another species such as Arabidopsis halleri. Genetic engineering technologies could be used to introduce or overexpress the relevant genes in Azolla, with the selection of the subspecies Azolla pinnata being a potential starting point.
**Genes:** 1. AtPCS1 - This gene encodes for phytochelatin synthase, an enzyme responsible for the biosynthesis of phytochelatins, a type of metal chelating compound. By overexpressing AtPCS1 in Azolla, the production of phytochelatins could be enhanced, leading to an increase in the ability of the fern to bind with silver ions.
2. HMA4 - This gene encodes for a protein involved in the transport of heavy metals, including silver, from the roots to the shoots in Arabidopsis. By introducing HMA4 into Azolla, the transport of silver ions from the root to the shoot could be improved, thereby enhancing the fern's ability to hyperaccumulate silver.
3. NAS1 - This gene encodes for nicotianamine synthase, an enzyme involved in the biosynthesis of nicotianamine, a metal chelator. Overexpression of NAS1 in Azolla could lead to the production of more nicotianamine, increasing the fern's ability to bind with silver ions.
4. NRAMP3 - This gene encodes for a protein involved in the transport of heavy metals, including silver, into the root cells. By overexpressing NRAMP3 in Azolla, the uptake of silver ions could be increased, leading to a higher accumulation of silver in the fern.
5. ACA9 - This gene encodes for a calcium-transporting ATPase, a type of protein involved in the transport of metals. By overexpressing ACA9 in Azolla, the accumulation of calcium ions could be increased, improving the fern's ability to cope with the stress of heavy metal toxicity.
6. GSTU19 - This gene encodes for glutathione S-transferase, an enzyme involved in the detoxification of heavy metals. By overexpressing GSTU19 in Azolla, the fern's ability to detoxify silver ions could be increased, reducing the toxicity of the metal in the fern.
**Regulatory Elements:** Promoter sequences:
1. CaMV 35S promoter – This promoter is derived from the Cauliflower mosaic virus and is known to work well in a wide range of plant species, including Azolla. It has been used extensively in plant genetic engineering studies and can drive strong and constitutive expression of the genes of interest in Azolla.
2. UBQ10 promoter – The UBQ10 promoter is derived from the Arabidopsis thaliana ubiquitin gene and is known to have a strong and constitutive expression in a variety of plant species, including Azolla. It has been used extensively in plant genetic engineering studies and can drive strong and constitutive expression of the genes of interest in Azolla.
3. P. patens actin 1 promoter – The actin 1 promoter derived from the moss Physcomitrella patens has been shown to have a strong and constitutive expression in mosses and other plant species. This promoter may be useful in driving strong and constitutive expression of the genes of interest in Azolla.
1. Octopine synthase enhancer – The octopine synthase enhancer (OSE) is derived from Agrobacterium tumefaciens and has been shown to enhance the expression of genes in a variety of plant species, including Azolla. The OSE has been used in numerous plant genetic engineering studies to increase gene expression levels.
2. Cauliflower mosaic virus enhancer – The cauliflower mosaic virus enhancer (CaMV-enh) has been shown to enhance gene expression in a variety of plant species, including Azolla. The CaMV-enh sequence is often used in combination with the CaMV 35S promoter to drive high levels of gene expression.
3. Asparagus officinalis fructose-1,6-bisphosphatase enhancer – The fructose-1,6-bisphosphatase enhancer from Asparagus officinalis has been shown to enhance gene expression in a variety of plant species, including Azolla. The enhancer sequence has been used in plant genetic engineering studies to drive high levels of gene expression.
1. Nopaline synthase terminator – The nopaline synthase terminator (NOS-t) is commonly used in plant genetic engineering studies as it has been shown to be functional in a wide range of plant species, including Azolla. The NOS-t sequence effectively terminates transcription of the transgene, preventing read-through of the transcript.
2. T7 terminator – The T7 terminator sequence is commonly used in bacterial expression systems and has been shown to be functional in some plant species, including Azolla. The T7 terminator is known to effectively terminate transcription of the transgene, preventing read-through.
3. Pisum sativum rbcS-E9 terminator – The rbcS-E9 terminator from pea (Pisum sativum) has been shown to be useful for terminating transcription of transgenes in some plant species, including Azolla. This terminator sequence may be useful in keeping the transcript of the transgene stable and preventing read-through.
Using these regulatory elements in the genetic modification of Azolla can enhance the desired outcome in various ways. The use of strong and constitutive promoters such as CaMV 35S, UBQ10, and P. patens actin 1 promoters can ensure that the genes of interest are expressed at high levels throughout the plant. This high level of expression can lead to an increase in the production of metal-chelating compounds such as phytochelatins and nicotianamine, as well as the transporters such as HMA4
**Vector & Delivery:** , NRAMP3, and ACA9 that are necessary for the plant to hyperaccumulate silver.
Additionally, the use of enhancer sequences such as OSE, CaMV-enh, and Asparagus officinalis fructose-1,6-bisphosphatase enhancer can further enhance the expression of the transgenes, leading to even higher levels of gene expression and ultimately increasing the fern's ability to hyperaccumulate silver.
The use of terminator sequences such as NOS-t, T7 terminator, and Pisum sativum rbcS-E9 terminator can ensure that the transcript of the transgene is stable and does not undergo read-through, leading to unwanted effects.
As for the vector, a binary vector system such as the pCAMBIA vector system could be used. This vector system contains multiple cloning sites and the ability to incorporate both the T-DNA and the helper plasmid, allowing for efficient transformation of the plant. Additionally, the T-DNA borders can be designed to incorporate the regulatory elements necessary for the expression of the transgenes.
The method of delivery would depend on the species of Azolla being used. If a strain of Azolla that can be grown in vitro is utilized, agrobacterium-mediated transformation could be used. This method involves introducing the binary vector system into the agrobacterium, which is then used to infect the plant tissue. However, if a strain of Azolla that grows only in water is used, biolistics could be utilized. Biolistics involve using a gene gun to transfer the DNA construct into the plant.
In summary, the use of strong and constitutive promoters, enhancer sequences, and terminator sequences can increase the expression of the transgenes responsible for hyperaccumulation of silver in Azolla. A binary vector system such as the pCAMBIA vector system can be used for efficient transformation, and the method of delivery would depend on the species of Azolla being used. By using these specific vectors and delivery methods, the desired genetic modifications can be optimized and ultimately lead to a successful hyperaccumulation of silver in Azolla.
**Selection Marker:** If a selection marker is deemed necessary for this project, we will use a visual marker such as Green Fluorescent Protein (GFP). This selection marker allows for the visual identification of successfully transformed cells, making it easier to select for and identify positive transformants. GFP does not confer any antibiotic resistance, and its expression can easily be detected non-destructively, allowing for the screening of a large number of transformants without harming the plant. In particular, using GFP can allow the selection of cells that exhibit the phenotypes of interests before the regeneration phase. Furthermore, the use of a visual marker like GFP eliminates the need for time-consuming and potentially hazardous antibiotic selection methods.
1. Preparing the Agrobacterium culture: Grow an Agrobacterium culture containing the binary vector with the desired transgenes and the selectable marker (if necessary), as well as the helper plasmid in appropriate media according to standard protocols.
2. Preparing the Azolla plant tissue: The Azolla plant tissue should be sterilized using appropriate surface sterilization protocols.
3. Transformation via Agrobacterium-mediated transformation: Take the sterilized Azolla plant tissue and place it into the Agrobacterium culture overnight in the dark. The bacteria will infect the plant tissue and transfer the T-DNA with the transgenes and selectable marker (if necessary) into the plants.
4. Post-transformation selection and regeneration: After the infection, the plant tissue should be washed with sterile water to remove any excess bacteria. The transformed tissue should then be placed on a selection medium containing the selective agent for the selectable marker (if used). After selection, the tissue can be regenerated into plants.
5. Genetic analysis of transgenic plants: Verification of transgene integration, expression, and inheritance using PCR, RT-PCR or other methods should be performed to confirm the presence, expression, and stability of the transgenes in the plant.
6. Phenotypic analysis of transgenic plants: The transformed plants should be analyzed for their ability to hyperaccumulate silver. The plants should be grown in media containing varying concentrations of silver to determine the optimal concentration for hyperaccumulation. The level of accumulation can be measured by atomic absorption spectroscopy or other appropriate methods. Finally, transgenic and control plants can be compared for their ability to accumulate silver to confirm the successful hyperaccumulation of silver in the transgenic plants.
1. Appropriate sterilization techniques should be used to ensure that no contamination occurs during the transformation process.
2. Specific precautions should be taken to prevent the release of genetically modified organisms and should comply with local and national regulations.
3. Careful monitoring and measurement of silver accumulation levels should be taken to ensure that the transgenic plants are accumulating silver safely and not causing environmental damage.
**Gene cassette**: The 5' to 3' list of elements in the multi-purpose cassette are as follows:
1. CaMV 35S promoter - to drive strong and constitutive expression of the genes of interest 2. AtPCS1 gene - responsible for the biosynthesis of phytochelatins 3. OSE enhancer - to enhance gene expression 4. HMA4 gene - involved in heavy metal transport from roots to shoots 5. NOS-t terminator - to effectively terminate transcription of the transgene 6. NAS1 gene - involved in biosynthesis of nicotianamine 7. GFP selection marker - to visually identify successfully transformed cells 8. UBQ10 promoter - to drive strong and constitutive expression of the genes of interest 9. NRAMP3 gene - involved in the transport of heavy metals into root cells 10. CaMV-enh enhancer - to enhance gene expression 11. T7 terminator - to effectively terminate transcription of the transgene 12. ACA9 gene - involved in the transport of metals 13. Pisum sativum rbcS-E9 terminator - to ensure stable transcript of transgene 14. GSTU19 gene - involved in detoxification of heavy metals 15. P. patens actin 1 promoter - to drive strong and constitutive expression of the genes of interest
The vector of choice is the pCAMBIA vector system, containing multiple cloning sites and the ability to incorporate both the T-DNA and the helper plasmid, allowing for efficient transformation of the plant. Agrobacterium-mediated transformation or biolistics could be utilized depending on the species of Azolla used.
If a selection marker is necessary, a GFP visual marker will be used to allow for the non-destructive screening of positive transformants.
**Paper Abstract:** The main objective of this project is to genetically modify Azolla to hyperaccumulate silver by introducing specific genes responsible for the production of metal-chelating compounds and the transport of heavy metals, and optimizing their expression using strong and constitutive promoters, enhancer sequences, and terminator sequences. The use of a binary vector system such as the pCAMBIA vector system and agrobacterium-mediated transformation or biolistics for delivery could be used, and a visual selection marker like GFP could be incorporated. The genes of interest include AtPCS1, HMA4, NAS1, NRAMP3, ACA9, and GSTU19. The successful hyperaccumulation of silver in Azolla could have implications for its use in phytoremediation of silver-contaminated environments, as well as potential commercial applications such as the production of silver nanoparticles.
**Growth, Selection & Stabilization:** Optimal Conditions for Growth and Selection:
Once the Azolla plants have been genetically modified, it is important to provide the optimal conditions for their growth and selection. Azolla is an aquatic fern that thrives in a symbiotic relationship with the cyanobacterium Anabaena azollae. Thus, it requires light, CO2, and nutrients in the water for growth.
The fern grows best in temperatures between 25-30°C, with pH levels between 5.5 to 7.5. Under these conditions, it is possible to grow Azolla in large quantities without causing stress to the plant, which can affect the effectiveness of the hyperaccumulation.
For the selection process, it is important to ensure the appropriate level of metal ion concentration. The optimal concentration of silver ions for selection will depend on the specific transformants produced. For example, If the modified Azolla is already strongly efficient in silver uptake, relatively low doses of silver, in the range of 5 to 10 μM, should be sufficient to inhibit non-modified, non-tolerant cells. Alternatively, if the overexpression of tolerance genes is not efficient, higher doses (above 10 μM) may be necessary to clearly discriminate between resistant and non-resistant lines.
Specific measures for stabilization:
Once the hyperaccumulation of silver in the Azolla has been achieved to satisfactory levels, it is important to stabilize the modified organisms to ensure that the altered traits are passed down through successive generations. One way to do this is by cultivating the modified organisms continuously in conditions that favor their growth and reproduction.
Furthermore, asexual reproduction via fragmentation can help to ensure that the modified traits are passed down to offspring. Additionally, regular screening of plants to ensure that the modified traits remain stable over generations can help to detect any instabilities at an early stage and enable corrective measures to be taken.
Overall, by ensuring the provision of optimal growing conditions and stabilizing the modified traits, the modified organisms can be made to thrive, leading to successful hyperaccumulation of silver by Azolla.
**Proliferation Method:** To proliferate the final transformants once stabilized, the method of tissue culture can be utilized. This involves growing plant cells or tissues in aseptic conditions on a nutrient medium supplemented with proper hormones and nutrients necessary for growth and proliferation. The tissue culture can be initiated from transformed explants such as leaves, callus, or shoot tips, which have been screened for the presence of the transgene using GFP or other selection markers.
Once the cells or tissues have grown and formed new shoots or roots, they can be transferred to another nutrient medium for further growth and development. This process can be repeated multiple times to proliferate the transformants and generate a population of plants with the desired genetic modifications. The use of tissue culture can ensure efficient proliferation of the transformants, as well as maintaining the stability of the transgenes in the resulting population.
Overall, the use of tissue culture can allow for efficient proliferation of stable transformants with the desired genetic modifications in Azolla, leading to successful hyperaccumulation of silver in the fern.
**Conclusion:** In conclusion, the project focused on genetically modifying the Azolla fern to hyperaccumulate silver, which can have significant implications for phytoremediation of silver-contaminated environments and potential commercial applications. The use of a binary vector system, a selection marker, and the introduction of specific genes such as AtPCS1, HMA4, NAS1, NRAMP3, ACA9, and GSTU19 could lead to successful hyperaccumulation. Optimal growth and selection conditions, as well as stabilization methods, can ensure efficient proliferation of the modified organisms. Future directions for research can include the optimization of gene expression, testing the viability of the modified organisms in the field, and exploring the potential for other heavy metal hyperaccumulation using similar methods. Overall, the project can be considered a success in demonstrating a potential solution to the problem of heavy metal pollution in the environment.