Clint Chapple, Ph.D.—
From Genomes to Plant Plastics Factories!

Clint Chapple, Ph.D., a product of the University of Guelph in Ontario, Canada, has been a professor of biochemistry at Purdue University since 1993. His research group—part of Purdue’s highly respected Plant Biology Program—recently made headlines when it was announced that Chapple, in conjunction with DuPont and Co., had collaborated on isolating and cloning a gene which would allow DuPont to grow crops that could be used to make plastics. We recently spoke with Dr. Chapple to learn more about his fantastic discovery and the fantastic, next-generation plastics which may result.

FoodTechSource.com: Exactly what role did your research group play in all this?

Clint Chapple, Ph.D.: We isolated the gene responsible for the synthesis of UV protective compounds in the common laboratory plant Arabidopsis. Our work is primarily basic research. However, DuPont learned about what we were doing and realized they might be able to use the gene we had isolated in the context of their research.

FTS: What does this gene do?

Chapple: The gene encodes an enzyme responsible for the last step in the biosynthesis of the UV protective metabolites. Essentially it catalyzes the step that makes the UV protective substance soluble in the vacuoles of the plant cells.

FTS: Vacuoles?

Chapple: Vacuoles are small structures within the cells which isolate compounds such as the UV protectants from the rest of the biochemical processes going on in the plant.

FTS: How does that fit into the DuPont work?

Chapple: DuPont had bioengineered a tobacco plant which could produce a new compound they wanted to use for the synthesis of plastics. The problem was, the compound was not accumulating at sufficiently high levels; it was being converted to a number of other metabolites in the plant cell and shunted off in different directions. DuPont hoped that by putting our gene into the mix, the compound they were interested in making would be converted to a much less metabolically active product, allowing it to accumulate as a single substance at higher concentrations. And our gene did exactly that.

“DuPont has bioengineered a tobacco plant which can be used for the synthesis of plastics.”

FTS: Is that as far as your work with DuPont went?

Chapple: We need to give credit where credit is due: The idea to use our gene in the context of plastics monomer production was entirely the idea of a gentleman by the name of Knut Meyer at DuPont. He had previously been a post doctoral research associate of mine, which is why he was aware of the research we were doing. So, our work with DuPont is continuing. We are isolating more genes of the same type with the hope that we’ll be able to make different kinds of conjugates that might be of use by DuPont.

FTS: Are you involved at all in the processing of the plastic monomers?

Chapple: No. It is important to realize we are at the very early, proof-of-concept stage of research. There is a lot more research to be done regarding the downstream processes. The challenge is now to the DuPont polymer chemists to explore what sort of new plastics they can make with these new monomers.
     Until now, polymer chemists have primarily made plastics and other polymers from petroleum derivatives, and petroleum offers the organic chemist a limited selection of monomers. Plants, on the other hand, are amazing chemical factories that produce a mind-boggling number of interesting chemicals—compounds the organic chemists haven’t previously been able to use for polymer synthesis. It presents the possibility for an array of new, innovative plastics.

FTS: You said DuPont was using the tobacco plant for their research. What plant do you use for your gene research?

Chapple: Arabidopsis. It is a common lab plant.

FTS: Is your work immediately applicable to all other plants?

Chapple: For the most part, yes. We work on the phenylpropanoid pathway in Arabidopsis. All plants have this pathway. So, the research we are doing in terms of understanding the catalysts in that pathway and how that pathway is regulated has application in regards to our understanding of how that pathway operates in other plants.
     To give you an example, other research we do focuses on lignin biosynthesis in Arabidopsis. Lignin is a polymer in the plant’s secondary cell wall that rigidifies the water conductive tissues of the plant and provides pathogen resistance. It also helps to hold the plant upright—the difference between a piece of celery and a piece of wood is the presence of lignin in the wood. During our research on the lignin biosynthetic pathway we have found ways of modifying lignin for the benefit of agriculture and forestry. It is a pathway common to all plants—one which effects the survival of all plants—so the work is applicable to other plants as well.

FTS: Why did DuPont choose tobacco?

Chapple: Tobacco is frequently the plant researchers will use first because it is an easy plant for inserting genes. It is easily transformable. So, you can take genes from Arabidopsis and put them into tobacco. On the other hand, you can put the same genes into corn, and you can put the corn genes into Arabidopsis...and they all, with very few exceptions, will function just fine. So, here again the genes we have isolated absolutely cross boundaries into other plants.

“You can take genes from Arabidopsis and put them into tobacco or corn or other crops and they will function just fine.”

FTS: How long have you been working on your Arabidopsis research?

Chapple: About ten years. We’ve been pursuing this particular aspect of research for the past three. And I’m happy to say we just received funding from the National Science Foundation to continue working to understand how these biochemical pathways function.

FTS: What was your initial reason for doing it?

Chapple: We’ve chosen to study this one particular pathway because of its importance to plant survival. In our lab we study the synthesis in plants of materials known as secondary metabolites. Your readers would recognize many of these compounds by smell or by flavoring if not by name or chemical structure. These are flavor components, odor components, pigments, alkaloids, etc. There are thought to be almost 100,000 different secondary metabolites and we were interested in identifying and understanding the genes responsible for the synthesis of these compounds; also, how their synthesis is regulated, and what these compounds do in plants. Once we have isolated the genes we can use them to manipulate metabolic pathways in order to improve plants for agriculture or forestry.

FTS: Research involving genetically modified organisms (GMOs) is a very politically sensitive area right now.

Chapple: That’s true. However, there is nothing I would like better than to see our basic research have some sort of impact. And while I respect the concerns of people worried about genetically modified organisms, I believe that biotechnology holds tremendous promise for the future. So long as appropriate safety measures are taken, this is not an inherently dangerous technology.

FTS: What kinds of precautions are you required to take in the lab?

Chapple: There are licensing requirements that we have to meet. Any person using recombinant DNA technology in a university lab must have their work approved by a university board. Part of that approval involves proper handling procedures associated with recombinant organisms, which means the bacteria we use in the lab and the plants we end up generating. Those recommended human procedures are designed to prevent release of any of these organisms into the environment.

FTS: How exactly do you go about identifying and cloning a gene?

Chapple: Paradoxically, it turns out that one of the best ways to understand what the function of a particular compound is in plants is to identify a plant that can’t make it. In the case of our UV protective metabolite you could certainly do this at a circumstantial level by looking at the compound and saying yes, it absorbs ultraviolet light and yes, it’s accumulated in the leaves so it is probably UV protective. However, the scientific evidence remains circumstantial. On the other hand, when we identified a mutant plant that was unable to make that compound we could actually test it and sure enough that plant was UV sensitive. You can then take that plant and use it to locate and identify the corresponding gene.
     We initially began studying Arabidopsis because it is a really good genetic organism. It also has the smallest genome of any known plant, which is what prompted the effort to sequence the genome—the results of which were released about a month ago. So, we look for Arabidopsis plants that are defective in the pathway we are studying, and once we have a mutant we can determine where that mutation exists on the genome. Is it on the top of chromosome 1 or on the bottom of chromosome 3? And using various molecular techniques we can focus on a narrower and narrower region where the gene must lie and eventually isolate the gene itself.

“We look for Arabidopsis plants that are defective in the pathway we are studying, and once we have a mutant we can determine where that mutation exists on the genome.”

FTS: And by isolating it you can then determine what its makeup is?

Chapple: Yes, you sequence the gene, and since the entire genome is sequenced this is getting to be an easier and easier task. You can determine what gene it is and then study how that gene is regulated; you can change the expression of that gene, you can turn it on at higher levels or you can knock it down in other plants; you can take that sequence information you derive from Arabidopsis and isolate the corresponding genes from other crop plants and study them there.

FTS: What do you foresee as the future of your research? How much farther do you think you’ll be able to go with what you’re doing right now?

Chapple: We’ve translated and determined the function of a handful of genes from Arabidopsis. There are many similar genes in Arabidopsis: for example one class of gene is called cytochrome P450-dependent monooxygenase (P450). There are almost 300 P450s in Arabidopsis and we know the function of only about a dozen. So, we have many more genes to explore; many new potential applications of those genes in other plants to look into.

FTS: How far do you think DuPont will be able to take the work you’ve given them?

Chapple: DuPont is only just starting. They have the opportunity to look at the synthesis of all sorts of different types of plastic monomers, and all sorts of different conjugates, such as the one we are working on together to try to synthesize. And then there are the challenges to the polymer chemists to find out what sorts of plastics they might be able to make with those monomers. We may see outcomes from this work in as little as five years if things go very very well. But there is plenty to keep researchers busy for years to come.

FTS: And how long has this concept been under examination?

Chapple: The idea of making new products from plants is something people have been looking into for probably ten years. This happens to be just a new spin on that idea.