Crop vaccines could help secure our global food supply, as new threats are constantly evolving. Preventing plant-disease outbreaks is an urgent matter — as urgent as having a rapid response strategy for human viruses. The same factors that quickly allow new human viruses to spread world-wide — global trade, traffic, and transport — also allow crop pathogens to spread.
We will never forget 2020 as the year of the coronavirus pandemic, but less remembered is the 2007-08 world food crisis that lead to poverty, malnutrition, and economic and social unrest in 48 countries. The United Nation declared 2020 the “Year of Plant Health,” as an effort to draw attention to this problem, but still little progress has been made in translating important scientific discoveries about plant immune systems into crops in the field. 2Blades Foundation is one organization that is on a mission to change that, through training young plants scientists and nurturing scientific discoveries through the plant science “valley of death” to commercialization.
Plants and plant pathogens have been locked in a millennia-long arms race. Plants have evolved natural defenses, but they turn spotty and ugly when they fight off pathogens. Not great for the supermarket shelf!
We use pesticides to grow beautiful produce, but they are costly, can be dangerous, and may damage the environment. For example, the world’s banana production is currently mortally threatened by Panama disease, the only way to fight it is with a pesticide that is toxic to soil. One of the most serious plant diseases in the world, citrus greening disease, is spread by infected insects, and there is no cure.
An often-cited statistic is that the world population is expected to exceed 9 billion people by 2050, and currently 800 million people do not have adequate food. We can expect that food production will only get more complicated by climate change and the loss of arable land. It has been estimated that 20 percent of the global harvest is lost to plant diseases.
The plant immune system has evolved to fight off pathogenic bacteria, nematodes, aphids, and fungi. There are two immune mechanisms in plants. One responds to slowly evolving dangers (like microbes) and sits on the outside of the plant cell. The other — “resistance” proteins — acts inside plant cells.
We know most of the resistance genes that code for those proteins. And they look a LOT like the proteins in the human immune system. They work much the same way, like a lock (protein) and key (pathogen). When the key fits into the lock, plants rally their troops to scuttle the invaders. Unlike the human immune system, plants are stuck with the genes they have. They cannot be adapted on the go to fight off new threats. Resistance genes are passed down from parent plants to offspring plants. The more genetic diversity there is, the healthier plants are, because there will be more variants of the resistance genes that can respond to a wide variety of threats.
If plants can fight off infections better, less pesticide can be used, and potential problems, like poisoning the good “predators of pests” and pests developing resistance to chemical treatments can be avoided. Crop “vaccines” could be the answer to fighting off quickly evolving pathogens, without genetically engineering the crop itself.
When a virus infects a plant cell, it often releases RNA — either in the form of messenger RNA or double-stranded RNA — which travels through the cell, helping the virus replicate. The resistance proteins can act like targeted scissors, that find the invader RNA and slice it to small pieces. Those small pieces (small interfering RNAs) are then used by the plant to find and target the viral RNA for destruction.
The sequence of small interfering RNAs can be predicted by computers and synthesized in a lab. The resulting nucleic acid cocktail can be applied directly to plant leaves — as a spray.
Studies are being carried out for these “non-transformative” (i.e. not genetic engineering) approaches to control insects, diseases, nematodes, and weeds, and it is expected that RNAi-based products will reach the market in the form of sprayable products for foliar application, trunk injection, root dipping, or seed treatment as direct control agents soon.
Monsanto is developing the use of RNAi through a technology called “BioDirect,” in which dsRNA formulation is applied to plants to protect against insect and pathogens. Syngenta scientists are also developing lines of biocontrol products based on RNAi to protect potato plants from the attack of the Colorado potato beetle. These technologies will help growers to improve pest control in crops, resulting in increased yields and improved quality.
In 2000, Eden Bioscience of Bothell, Washington, released Messenger, an EPA approved based on harpin — the protein byproduct of a bacterial pathogen. Plants think they are being invaded, so they rally their natural immunity, simply activating their immune systems. This protein-based (not RNA-based) technology performs well on cucurbits, potatoes, strawberries, and tobacco, but not as well on cherries, apples and grapes. It’s incredible to think this technology is already 20 years old!
Many more examples like these should be developed, and governments worldwide should coordinate on rapid response initiatives for when the next global food crisis or crop pandemic strikes. As terrifying and economically devastating as the coronavirus pandemic has been, there actually are much worse scenarios to worry about. Raising awareness of the issues, technologies, and commercialization “valley of death” is simply the first step in securing the future of food for our planet.
Besides developing vaccines for plants themselves, plants could one day manufacture vaccines for us!