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The DOST-Biosafety Committee, in support of its continuing knowledge enhancement, invited Prof. Neena Mitter, Director of the Centre for Horticultural Science of the University of Queensland (UQ), Australia to give a presentation during its January meeting to discuss the use of RNA to protect crops from pest and diseases via Zoom platform.  

Prof. Mitter is also the Director of the Australian Research Council Industrial Transformation Research Hub for Sustainable Crop Protection. She is globally renowned for her leadership on innovative platforms, examples of which are the ‘environmentally sustainable BioClay platform for crop protection’ and ‘clonal propagation of avocado using plant stem cells’.  These are ground-breaking platform technologies influencing agricultural production, environmental sustainability, and socio-economic dynamics of the global farming community. Her career and passion for delivering real world solutions has received recognitions as Fellow of the Australian Academy of Technology and Engineering, 2021 Pravasi Fellow of the Indian National Academy of Agricultural Sciences, Australian Women in Technology Outstanding Life Sciences Award and Gates Grand Challenges Explorations Award. Prof. Mitter has been selected to champion a UQ wide initiative on ‘Protected Cropping for Tropics and Subtropics’ and across the University, is leading the development of clean technologies for the agriculture of tomorrow.  She has more than 120 publications and since 2011 has supervised more than twenty (20) PhD students.  As Chairperson of UQ Cultural Inclusion Council and Deputy Council member of the Australian Human Rights Commission Leadership Council on Cultural Diversity, Prof. Mitter is at the forefront of diversity and inclusion initiatives.

Prof. Mitter started her presentation with a question “why do we need to protect our crops from pest and diseases?” She emphasized the damages brought by these pest and diseases amounting to 40% wastage of global crops yields, understanding the need of the small farmers wanting to yield more healthy produce. The damages brought by these pest and diseases also contribute to the growing number of children that go to school with an empty stomach. She mentioned that it would take thirteen (13) years to conduct research, develop and register a new crop protection product, with an estimate of 1 out of 39,000 chemicals making it from the laboratory to the farmers.

Prof. Mitter then cited the challenges of using crop pesticides, such as resistance development, pesticide residues that are not healthy for human consumption and the environment. Said residues could also lead to runoff to waterways that could cause contamination to the environment. Another is lack of specificity. As much as we want to exterminate the pest, Prof. Mitter stated that beneficial organisms such as bees, butterflies and other useful microorganism must be safeguarded. With these challenges at hand, it is also worrisome that new chemicals are hard to come by to immediately address the problem.  

Prof. Mitter recalled that the 2013 news article from Reuters about pesticide contaminated meal that killed 25 Indian children, triggered her interest to look for a safe method of crop protection and work in the area of RNA.

“RNA interference or Gene silencing”

Gene silencing is a method of targeting and immobilizing a critical gene in the pest or pathogen, and once the gene is not able to function, the pest will not be able to survive. Dr. Mitter mentioned that this technology is not new, that it started with the genetic modification of crops. The genetically modified plant will express the double stranded RNA which silence the gene of the pest or pathogen when it attacks the genetically modified plants. Prof. Mitter acknowledged that this technology will have issues, such as regulatory issues, cost and time involved in developing the GM plant, and eventually when it reaches the market/consumers in terms of public acceptance. She also recognized the difficulty in developing other tropical fruit crops/trees such as mango, bananas, pineapples and avocados, due to lack of transformation protocols.

The concept was then born using RNA- based biopesticides or RNA vaccines for crops as a topical or spray application. Prof. Mitter mentioned that since 2003, there are papers/researches that show group of scientists experimenting on virus-infected leaf, half of it is sprayed with biopesticides and the other half unsprayed.  

She recognized that there are limitations of using dsRNA because it is easily degraded by sunlight within 2-3 days it is affected by UV, sunlight, can be easily degraded on plant surface, easily washed off leaves and has a short protection window of just about 3-5 days.

The challenge was how to stabilize the dsRNA and convert into a commercially viable system that is environment-friendly, non-toxic, easy to adopt and no runoff issues. In the new plartform called BioClay, RNA is the biological active ingredient and the clay particles serve as carriers. Once RNA is loaded on the clay particles, it can make it stable and last longer without leaving any residue. The project was initially funded by the Bill and Melinda Gates Foundation and work on its commercialization is on-going.

So how does BioClay work? They used inert biodegradable clay to deliver the RNA. It is applied as a spray application without the need to alter the plant genome. The clay layers are made up of Mg and Fe, which serves as nutrition for the plant as well. It degrades naturally, leaving no residue, therefore, it has no toxicity issue. It has extended stability and slow release of dsRNA on plant surface. It is almost like nature vs nature because they are using the dsRNA of the pest/pathogen to kill itself.  

Prof. Mitter presented the technology to the scientific community to convince them that BioClay works by demonstrating that a) BioClay dsRNA survives on leaf surface even after 30 days of spray; b) the sprayed dsRNA can enter the plant system; c) BioClay does not get washed off by water/rain; and d) the sprayed leaves are protected from virus even after 20 days of spray.

To date, a lot of work has been done on a number of virus diseases such as tomato and capsicum plants infected with tomato spotted wilt virus, zucchini yellow mosaic virus, viruses of cucurbits, cucumbers, potatoes, squash and melon. They are also working on insect pests as well, such as in cotton and other horticultural crops damaged by the silverleaf whitefly.

They are also looking at a number of biosecurity risks, and some of the pest and pathogens which are really causing damage are fall army worm and fruit flies which is a major export issue. They have also extended the platform to include fungal diseases because they saw that fungi can take up RNAs from the environment. Some fungal pathogens of interest are Botrytis spp., myrtle rust, Phytophthora root rot and heart rot in pineapple and avocado

As for safety considerations such as risks to the environment, non-formulated dsRNA rapidly degrades in the environment, presenting few risks related to persistence and there is no basis for concentration of topically-applied dsRNA in higher organisms in the food chain. 

There is also no concern on its risk to human health since there are multiple and redundant biological barriers to absorption and/or biodistribution. People have been consuming significant quantities of dsRNAs and siRNAs via a diet of fruit and vegetables without detectable effect and miRNA studies indicate insufficient uptake for biologically relevant effects.

The Food Standards Australia New Zealand (FSANZ) has already issued a statement on dsRNA consumption stating that  1) gene silencing or RNAi is a universal mechanism that is naturally present in eukaryotic organisms; 2) dsRNAs are a normal constituent of the human diet; 3) a number of barrier exist to the systemic and cellular uptake of exogenous nucleic acids, including small RNAs, by humans; and 4) there is no scientific basis for presuming that dsRNAs produced by GM plants would pose a greater risk than dsRNAs naturally present in food.

Prof Mitter likewise informed the Committee that on 8th October 2019, the Australian Parliament formally agreed with the Office of the Gene Technology Regulator’s (OGTR) that topically-applied dsRNA be exempt from GMO regulations.

Prof. Mitter in closing, stated that RNA-based biopesticides is a paradigm shift in a sense that it can be used both during pre- and post-harvest application, it has increased pest/pathogen specificity, that new genetic sequences can be easily deploy to address resistance, it has a finite amount of dsRNA and more importantly, it is considered non-GM.