Researchers Discover Gene That Could Be Key in Hardwood Evolution
Researchers in the School
of Forestry and Wood Products have discovered a gene that may have played
a key role in the evolution of hardwood trees such as oaks and maples.
Their work is featured on the cover of the July issue of The Plant
Cell, which ranks first in impact among plant science-related journals.
Millions of years ago, gymnosperms--including
conifers such as pines and redwoods--were the only type of plants on earth.
Then angiosperms--the flowering plants--appeared, among them hardwood
trees.
While angiosperms are considered
more advanced than gymnosperms, their origins largely remain a mystery.
At least a part of that mystery may now be solved, thanks to the work
of lead author Research Assistant Professor Laigen Li and researchers
at the School's Plant Biotechnology Research Center.
The researchers, including
Professor Vincent Chiang, the center's director, have described the genetic
pathway used to create syringyl lignin, a type of lignin that is unique
to angiosperms. Lignin is found in all trees and is the substance that
makes them stiff. But in gymnosperms, also known as softwoods, only guaiacyl
lignin is present. In hardwoods, both guaiacyl and syringyl lignin are
found.
The researchers identified
and, for the first time, cloned a gene from aspen, an angiosperm, which
they suspected was responsible for producing syringyl lignin. They introduced
the gene into E. coli bacteria, and found that it produced a protein
with a very specific purpose: It assembled hardwoods' syringyl lignin.
For years, most scientists
have believed that another gene controlled the production of both lignin
types. "But we thought it didn't make sense for plants to evolve
new proteins and still use the old gene," Chiang said. "Our
discovery of a syringyl-specific gene overturns that traditional model;
it's been very exciting."
The researchers also have identified
two characteristics of syringyl lignin that could give hardwoods an evolutionary
advantage. Before angiosperms appeared, the function of lignin in plants
was primarily to conduct water and other nutrients. In angiosperms, however,
syringyl lignin took on an important mechanical role, serving as the "skeleton"
for angiosperm trees. In addition, Chiang notes, the syringyl lignin molecule
includes additional methoxyl (H3CO) groups that the researchers suspect
increase its toxicity. A tree with this type of lignin could be less vulnerable
to disease, Chiang said.
To view the article, visit
http://www.plantcell.org/
The
article, "The Last Step of Syringyl Monolignol Biosynthese in Angiosperms
Is Regulated by a Novel Gene Encoding Sinapyl Alcohol Dehydrogenase,"
is the first on the subject of a tree species to appear in The Plant
Cell since the journal was first published twelve years ago. In addition
to Li and Chiang, the coauthors are Postdoctoral Research Scientist Xio
Fei Cheng, Research Assistant Professor Scott Harding (SFWP), Jacqueline
Leshkevich (formerly of Michigan Tech), and Toshiaki Umezawa of Kyoto
University.
