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Polymeric nanocarriers improve crop engineering by delivering proteins across cell walls

(Nanowerk Spotlight) Advances in plant biotechnology have long been frustrated by a stubborn obstacle: the impermeable cell walls that shield plant cells from foreign molecules. Delivering functional proteins into these cells has remained a formidable challenge, stalling progress in areas like crop improvement and stress monitoring. Traditional methods, such as viral vectors and gene guns, often fall short due to their limitations in host range and potential to damage plant tissues.
However, a new frontier in nanotechnology is beginning to crack this barrier, offering a novel approach to plant engineering that could redefine the field.
In recent research, published in Advanced Materials ("Polymeric Nanocarriers Autonomously Cross the Plant Cell Wall and Enable Protein Delivery for Stress Sensing"), scientists have developed polymeric nanocarriers (PNCs) that autonomously traverse plant cell walls, delivering functional proteins directly into the cells with unprecedented efficiency. These nanocarriers, engineered to be cationic – positively charged – are designed to bind tightly with proteins and transport them through the plant’s natural defenses.
These PNCs are engineered with a high aspect ratio, meaning they are long and thin, which is essential for their ability to penetrate the plant cell wall. The study found that PNCs with a width below approximately 14 nanometers can pass through the cell wall, carrying their protein cargo into the cell without requiring external forces or additional chemical treatments.
Synthesis and characterization of cationic high aspect ratio polymer nanocarrier for protein delivery in plants and their complexation with protein
Synthesis and characterization of cationic high aspect ratio polymer nanocarrier (PNC) for protein delivery in plants and their complexation with protein. a) Synthesis procedure of high aspect ratio bottlebrush polymer nanocarriers with permanent positive charge. b) Protein grafting onto cationic PNCs. (Image: Adapted from DOI:10.1002/adma.202409356, CC BY)
To demonstrate the practical application of these PNCs, the researchers utilized a reduction-oxidation (redox) sensitive green fluorescent protein (roGFP) as a model cargo. This protein acts as a stress sensor by changing its fluorescence in response to reactive oxygen species (ROS), which are generated in plant cells under stress conditions such as wounding, pathogen attack, or heat exposure.
In their experiments, the researchers successfully delivered the roGFP into three plant species: Nicotiana benthamiana (a model plant), tomato, and maize. These species were chosen to represent both dicotyledonous (dicot) and monocotyledonous (monocot) plants, showcasing the versatility of the PNC platform. After delivery, the roGFP allowed the researchers to monitor plant responses to various stressors in real-time, a capability that could be transformative for agricultural practices.
One of the critical findings of the study is that the efficiency of protein delivery is highly dependent on the size and charge of the PNCs. PNCs with a width greater than 14 nanometers or with insufficient positive charge were less effective at penetrating the plant cell wall and delivering their protein cargo. This insight into the physical requirements for successful protein delivery could guide the design of future nanocarriers for a wide range of plant engineering applications.
Moreover, the PNCs developed in this study offer several advantages over traditional methods of protein delivery. They enable the delivery of functional proteins directly into mature plants, bypassing the need for transgenic methods that involve modifying the plant's DNA. This not only speeds up the process of plant engineering but also avoids some of the ethical and regulatory concerns associated with genetically modified organisms (GMOs).
The implications of this research are broad and significant. By enabling the direct delivery of functional proteins into plants, these PNCs could be used to enhance crop resilience to environmental stresses, improve yields, and reduce the need for chemical inputs such as fertilizers and pesticides. Additionally, this technology could be applied to the development of "sentinel plants" that can monitor environmental conditions and provide early warnings of stress, disease, or pest infestations, allowing for more targeted and sustainable agricultural practices.
While the study primarily focused on the delivery of stress sensor proteins, the potential applications of this technology extend far beyond stress monitoring. For example, the delivery of proteins involved in photosynthesis could enhance the efficiency of this critical process, leading to higher crop yields. Alternatively, proteins that confer resistance to pathogens could be delivered to crops in regions where diseases are a significant threat to food security.
Schematic illustration of polymer nanocarrier enables protein uptake into plant cell
Schematic illustration of polymer nanocarrier enables protein uptake into plant cell. (Image: Adapted from DOI:10.1002/adma.202409356, CC BY)
Despite these promising developments, challenges remain. The study notes that while the PNCs were effective in delivering relatively small and stable proteins like roGFP, larger and less stable proteins, such as the Cas9 ribonucleoprotein (a tool used in gene editing), may present additional challenges. Future research will need to focus on optimizing PNCs for the delivery of these more complex proteins.
Another area for further exploration is the development of portable and field-deployable detection systems that can utilize the stress-sensing capabilities of proteins like roGFP. While the current study used confocal laser scanning microscopy to monitor the delivered proteins, this approach is not practical for large-scale agricultural applications. Developing affordable, portable sensors that can be used in the field will be essential for translating this technology into real-world agricultural practices.
The development of polymeric nanocarriers that can autonomously cross the plant cell wall and deliver functional proteins represents a significant advancement in the field of plant biotechnology. This technology holds the potential to revolutionize plant engineering by providing a practical, scalable method for delivering a wide range of proteins into plants. As research continues, these PNCs could play a critical role in addressing some of the most pressing challenges in agriculture, including improving crop resilience, increasing yields, and reducing the environmental impact of farming practices.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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