On Christmas Eve 2020, a group of scientists released a report on a revolutionary new method for battling COVID-19. As a couple of ag researchers read through the findings, they became more and more excited. The potential of the described technology seemed almost limitless. Nanobodies, a tiny piece of the antibody cells found in the camelid animal family (camels, llamas, and so on), could interfere with just about any cellular organism, including bacteria and viruses.
One of those scientists reading the study results was Michelle Heck, PhD, Emerging Pests and Pathogens Research Molecular Biologist, USDA-ARS, who quickly reached out to her Florida colleagues, Robert Shatters, PhD, Research Molecular Biologist, USDA-ARS, and Marco Pitino, Lead Project Scientist at AgroSource. They were leading a team trying to find a way to battle citrus greening.
Heck, Shatters, and Pitino set out to do the following: See if plants and symbionts could produce nanobodies against COVID-19 and citrus greening disease, and find a cost-effective way to deliver nanobodies to trees to fight against the disease.
The trio recently released their own study showing proof of concept for these ideas.
Naturally, I had a lot of questions on nanobodies. Here is a small part of a Q&A with Heck and Shatters.
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How do nanobodies work?
Heck: [In citrus greening], the bacteria express these little weapons proteins called effector molecules/ effector proteins. [An effector molecule is a small molecule that selectively binds to host molecules and regulates their biological activity and this activity can induce disease symptoms.]
If the bacterial infection starts here in the plant or on this leaf, the bacteria will secrete effector proteins that move to the other part of the plant to dampen the plant’s immune system and create an environment that supports pathogen growth.
And so, we hypothesized that if we developed a way to block those bacterial effector molecules from working, we could stop the infection process in its track.
Your paper mentions using symbionts — living cells that need the plant to live but don’t harm it — as a delivery system. How does that work?
Shatters: One of the things that came up over and over was this idea of, what if we could make something like an insulin pump they strap on a tree and it delivers a proper dose over time? But we’ve got to do it biologically, because we can’t afford to put a mechanical pump on every tree.
But if the tree could do that…
And so we came up with this concept of rethinking how people make transgenic plants. And that’s what the symbiont is.
We take some cells from the plant, we modify them with genes to produce growth hormones, so they grow into what we call a symbiont. It’s a group of citrus cells that grow where they are attached to the tree and do not move from that location. So we engineer them to produce things that we want them to produce, molecules such as nanobodies or other molecules that can act as a defense against the bacterium that causes citrus greening disease.
You say this symbiont can be used on just about anything, including citrus trees and tomatoes. But how? A tree has bark, a cambium – its vascular system is significantly different from a tomato’s.
Heck: The application method we use involves sort of creating a small site of injury, a small bark flap, where we apply that group of cells. Since that group of cells is expressing plant growth regulators amazingly, it’s enough to recruit the development of new vascular tissue right to that site of growing cells. They essentially adapt in their size and structure and texture to whatever host it attaches to.
For more of the conversation, continue reading the full article featured as part of our special Global Insight Series report on Soil Health. In addition, check out the previous reports in Meister’s Global Insight Series covering a range of topics.
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