Targeting the chloroplasts of plants, instead of their nucleus, this revolutionary method provides a super-precise, safer, stable and low-cost chloroplast-transformation in crops, using 1,000 times less DNA.

Singapore – Scientists at the Singapore-MIT Alliance for Research and Technology (SMART) at CREATE in Singapore, have invented an innovative nanotube carrier that is absorbed by the leaf of the plant to transform the genes of its chloroplast. Depending on the DNA inserted, this nanotube carrier can help bring about an improvement to the plant’s agronomic traits and disease resistance. And because this carrier only targets the chloroplast of the plant, it ensures that the natural hereditary genetics of the plant is not compromised at all.

This research, “Chloroplast-selective Gene Delivery and Expression in planta using Chitosan-complexed Single-walled Carbon Nanotube Carriers” was led by SMART Interdisciplinary Research Group (IRG) – Disruptive & Sustainable Technologies for Agricultural Precision (DiSTAP) – and will be published by early March 2019, in the prestigious academic journal Nature Nanotechnology. It is the first demonstration of a nanoparticle-mediated approach capable of enabling chloroplast-selective gene delivery for transgene expression in mature plants, without the aid of external chemical or mechanical force.

DiSTAP IRG, a collaboration between SMART and Temasek Life Sciences Laboratory (TLL), aims to address deep problems in food production in Singapore and the world. The DiSTAP programme is developing a suite of impactful and novel analytical, genetic and biosynthetic technologies that will fundamentally change how plant biosynthetic pathways are discovered, monitored, engineered and ultimately translated to meet the global demand for food and nutrients.

Mechanism of nanotube carrier
Through a method called lipid exchange envelope penetration, SMART scientists injected the Single-Walled Carbon Nanotubes (SWCNT) to the underside of the leaf via a watery solution which is absorbed through tiny pores called stomata. The transfer across the lipid membrane of the chloroplast was made possible by coating the nanotubes in negatively charged DNA. The team found that nanoparticles that are either strongly negative or positively charged can traverse the fatty membrane of the chloroplast. The lipids that make up the membrane grab onto the particle surface and draw it into the organelle. Once inside, the nanoparticle can function as a molecular sensor or in the case of this work, can release a genetic payload that allows for the engineering of the plant.

Lead author, SMART Research Scientist, Dr Seon-Yeong KWAK [郭善英], said: “This technology is the first-of-its-kind as it allows chloroplasts transformation to take place without killing the plant or its leaf. We able to use 1,000 times less DNA compared to conventional plant genetic engineering methods to genetically modify the chloroplasts. By specifically targeting the chloroplasts, there is significantly reduced risk of accidental cross-pollination to undesired plants.”

Co-lead author at MIT, Mr Tedrick Thomas Salim LEW [林志德], elaborated: “Using the mathematical model that we developed, we can design nanoparticles that can efficiently target the chloroplasts while carrying and protecting the DNA payload from cellular degradation. We demonstrated that the technique can be applied to various plant species such as spinach, watercress and arugula, offering new opportunities in aiding crop improvement and plant biology studies.”

DiSTAP Lead Principal Investigator, Prof Michael Strano said: "This new tool should reduce the work and time needed to engineer plants for human use. Scientist and farmers alike will benefit from a carrier that can access the chloroplast and do so across many different plant species. This work highlights the power of nanotechnology to solve longstanding challenges in the biological sciences."

Prof Chua Nam Hai, Deputy Chairman of TLL said: “We are excited to work with the SMART research team to develop novel technologies for enhancing food sustainability by combining plant biology with nanotechnology. This discovery of this nanotube technology will help shorten the time needed for candidate genes screening and contribute to the development of improved plant products for the efficient and sustainable production of food for Singapore and globally.”

The research was funded by the Singapore National Research Foundation (NRF) through SMART at the Campus for Research Excellence And Technological Enterprise (CREATE).

For more, please see media coverage on Straits Times, Lianhe Zaobao and Channel NewsAsia.