Plants make two types of lignin, syringyl lignin and guaiacyl lignin. The lignins are alike in many ways, but there's a difference in the way they break down. Syringyl lignin is relatively easy to digest and degrade. Guaiacyl lignin is tougher stuff.
The genes Chapple found and is in the process of patenting cause plants to make only easy-to-degrade syringyl lignin. He is convinced that they can be used to transform and breed trees that are easier to process, helping processors get more pulp per tree and reducing the need for some harmful chemicals. He also believes that the same genes can make alfalfa, corn and grass more digestible for livestock. A number of companies already have expressed interest in licensing the genes from Purdue.
Chapple's findings sprouted from his fascination with the unusual chemicals that plants make to help themselves, but which people also find useful. Pyrethrins, for example, are compounds that plants make to ward off insect pests -- and which people extract from plants for the same purpose. Opium poppies make morphine to stop animals from feeding on them, but people use morphine and its derivatives for pain relief.
"We want to understand how and why plants make chemicals like these," Chapple says, "because of their potential agricultural importance."
Chapple chose to work with Arabidopsis , a tiny member of the mustard family that grows, flowers and dies in just two months. It has the smallest number of genes of any flowering plant. For these and many other reasons, Arabidopsis is one of the best-studied plants on the globe.
"Arabidopsis is an excellent model for research partially because so many people are currently working with it," Chapple says. "We've learned a lot about all plants by working with Arabidopsis ."
Chapple found that Arabidopsis made a chemical, sinapoylmalate, that protects it from ultraviolet (UV) light. Without such protection, UV light would kill the plant.
In 1990, Chapple started working to create mutant Arabidopsis plants that lacked the UV-absorbing compound. By 1991 he had created such a mutant, and he added a marker gene that pinpointed the location of the genetic defect. With the marker, he went back into the DNA of normal Arabidopsis plants, found the location of the corresponding gene, and using techniques of biotechnology, pulled out a normal, nonmutated copy. Then he figured out what had gone haywire in the biochemical pathway that leads to the production of the UV-absorbing compound.
About halfway through that pathway Chapple found the enzyme ferulate-5-hydroxylase (F5H). It was F5H that his mutant plants lacked. Without F5H the plants couldn't create the UV-absorber.
As Chapple studied the enzyme chain, he stumbled across another important discovery: The F5H enzyme is key in determining whether plants make the easy-to-degrade syringyl lignin or hard-to-degrade guaiacyl lignin.
When Arabidopsis systems are working normally, much of the lignin they make is in the form of easy-to-degrade syringyl lignin. When F5H is missing or scarce, as it is in Chapple's UV-sensitive mutants, they mostly make guaiacyl lignin, the type that is hard to degrade.
Chapple knew that no manufacturers would beat a path to his door for this discovery. Nobody wants trees that are harder to process or plants that are harder to digest.
On the other hand, thought Chapple, maybe he could use what he had learned about F5H to increase, rather than decrease, the levels of the F5H enzyme. Plants with more of the F5H enzyme might produce more of the easily degradable syringyl lignin.
Chapple, an associate professor of biochemistry, and his co-workers immediately set out to make an F5H-rich Arabidopsis plant.
After a couple of tries, they produced a plant that made only the easy-to-degrade syringyl lignin. They also found that plants rich in syringyl lignin grew and looked exactly like normal Arabidopsis . The genes responsible for the transformation worked similarly in tobacco plants, which led Chapple to believe they will work in trees, alfalfa, corn, grass and other plants and spurred him to pursue a patent.
Patents didn't appear in even his wildest dreams when Chapple started working on UV-protection in Arabidopsis . He began by pursuing a fascinating bit of basic research. Chapple says he has an abiding faith that good minds asking good questions about basic processes can bring to light problems that people haven't yet thought of solving. Sometimes scientists even find answers before they define a problem.
"When they invented the laser back in the 1950s, nobody dreamed that it would save grandma's vision in the 1990s, but it did," Chapple says. "Basic science is like that. We can't always tell where the next scientific advance is going to come from."
Source: Clint Chapple, (765) 494-0494; e-mail, firstname.lastname@example.org
Writer: Rebecca J. Goetz, (765) 494-0461; e-mail, email@example.com
Purdue News Service: (765) 494-2096; e-mail, firstname.lastname@example.org
Purdue biochemist Clint Chapple raises Arabidopsis
plants in a growth chamber. His research with the plants could help the wood industry
produce paper with less waste and fewer harmful chemicals. (Agricultural Communication
Service Photo by Mike Kerper)
Color photo, electronic transmission, and Web and ftp download available. Photo ID: Chapple/Lignin
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