News Services
North Carolina State University
Campus Box 7504 Raleigh, NC 27695
(919) 515-3470
Media Contacts:
Dr. Ronald R. Sederoff, 919/515-7800 or [email protected]
Dr. David M. O'Malley, 919/515-7800 or [email protected]
Tim Lucas, News Services, 919/515-3470 or [email protected]
July 21, 1997
Mutant Pine's Abnormal Wood May Yield Environmental Benefits
FOR IMMEDIATE RELEASE
Breeding trees that can be more easily processed into paper, with less harm to the environment, has long been a goal of researchers. Now, thanks to the discovery of abnormal, brown-colored wood in a mutant pine tree, scientists at North Carolina State University may be a step closer to achieving that goal.
"Preliminary experiments suggest this mutant wood contains lignin that can, under certain circumstances, be removed from wood pulp with less waste, using fewer chemicals, than normal lignin," says Dr. Ronald R. Sederoff, director of NC State's Forestry Biotechnology Program.
Lignin is a substance that gives trees their stiffness. It must be removed before wood pulp can be made into paper. Conventional removal processes for normal lignin require the use of high temperatures, high pressure and harsh chemicals. Tests at NC State suggest the abnormal lignin can be efficiently removed from wood in a soda-pulping process.
The mutation -- the first ever identified in a woody plant -- was found in a healthy, 40-year-old loblolly pine. Scientists from NC State and the U.S. Dairy Forage Research Center at the University of Wisconsin-Madison worked jointly to identify and characterize it.
The researchers published their findings in the July 11 issue of Science. They will publish a second article in the July 22 issue of Proceedings of the National Academy of Sciences.
While Sederoff and his colleagues still don't know for sure why the wood in the mutant tree turns brown, they do know what causes the mutation and how it is passed along to a tree's progeny.
"Mutant plants must be homozygous, which means they're the product of inbreeding in which both parents pass along the recessive gene needed for the mutation," says Dr. David M. O'Malley, research assistant professor in NC State's Forestry Biotechnology Program. The wood of trees receiving a recessive gene from only one parent does not exhibit the characteristic brown color, he says. Instead, it is nearly white, like the wood of normal pines.
In homozygous mutants, expression of the cinnamyl alcohol dehydrogenase (CAD) gene is greatly reduced. CAD plays a key role in the conversion of coniferaldehyde, a CAD substrate, into coniferyl alcohol, an important lignin precursor in pines. When expression of CAD is deficient, this synthesis does not occur. Instead, unconverted coniferaldehyde builds up and is incorporated into the lignin, altering its chemical composition.
In a previous experiment in 1995, NC State scientists successfully cloned the gene that encodes the CAD enzyme in loblolly pines. This ability, coupled with the new knowledge gleaned from characterizing the abnormal lignin, should speed researchers' effort to make their findings practicable for industry, O'Malley says.
In addition to its possible benefits for pulping, the discovery of the abnormal lignin opens new avenues of investigation for plant geneticists and biological engineers, says Sederoff, a member of the National Academy of Sciences. "Previously, we thought if we altered lignin too much, it would be lethal to the plant. Yet here's a mutation that goes far beyond what we thought possible in a healthy plant. It lets us know lignin can be manipulated, naturally or by genetic engineering, far more than we ever expected."
That could mean scientists will one day be able to genetically tailor the concentration or type of lignin in a tree to its end use. "Conceivably, we could engineer some trees to be superior for pulping, others for lumber production," says O'Malley. The benefits would also extend beyond the forest products industry, he notes. Forage plants with less lignin would be more digestible by dairy cattle and other grazing livestock.
Other NC State researchers who contributed to the article in Proceedings of the National Academy of Sciences are Dr. Ross W. Whetten, research assistant professor of forestry; Dr. Fitzgerald L. Booker, crop science researcher; Dr. Malcolm M. Campbell, formerly of NC State and now at Oxford University; Dr. John J. MacKay, a former doctoral candidate in genetics; and Dr. Timothy Presnell, formerly of the Department of Wood and Paper Science and now at Westvaco.
Co-authors of the Science article from the U.S. Dairy Forage Research Center are Drs. John Ralph and Ronald D. Hatfield.
-- lucas --
NOTE TO EDITORS: Abstracts from the papers published in Science and Proceedings of the National Academy of Sciences, follow. For a copy of the articles, contact Tim Lucas, NC State News Services, at (919) 515-3470 or [email protected]
Inheritance, Gene Expression and Lignin Characteristics in a
Mutant Pine Deficient in Cinnamyl Alcohol Dehydrogenase
by John J. MacKay, David M. O'Malley, Fitzgerald L. Booker, Timothy Pressnell,
Malcolm M. Campbell, Ross W. Whetten and Ronald R. Sederoff
published in the July 22, 1997, Proceedings of the National Academy of Sciences
ABSTRACT: We have discovered a mutant loblolly pine (Pinus taeda L. ) in which expression of the gene encoding cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) is severely reduced. The products of CAD, cinnamyl alcohols, are the precursor of lignin, a major cell wall polymer of plant vascular tissues. Lignin composition in this mutant shows dramatic modifications, including increased incorporation of the substrate of CAD (coniferaldehyde), indicating that CAD may modulate lignin composition in pine. The recessive cad-1 allele, which causes this phenotype, was discovered in a tree heterozygous for this mutant allele. It is inherited as a simple Mendelian locus that maps to the same genomic region as the cad locus. In mutant plants, CAD activity and abundance of cad RNA transcript are low, and free CAD substrate accumulates to a high level. The wood of the mutant is brown, whereas the wood in wild types is nearly white. The wood phenotype resembles that of brown midrib (bm) mutants and some transgenic plants in which xylem is red-brown due to a reduction in CAD activity. However, unlike transgenics with reduced CAD, the pine mutant has decreased lignin content. Wood in which the composition of lignin varies beyond previous expectations still provides vascular function and mechanical support.
Abnormal Lignin in a Loblolly Pine Mutant
by John Ralph, John J. MacKay, Ronald D. Hatfield,
David M. O'Malley, Ross W. Whetten and Ronald R. Sederoff
published in the July 11, 1997, issue of Science
ABSTRACT: Novel lignin is formed in a mutant loblolly pine (Pinus taeda L.) severely depleted in cinnamyl alcohol dehydrogenase. (E.C. 1.1.1.195) which converts coniferaldehyde to coniferyl alcohol, the primary lignin precursor in pines. Dihydroconiferyl alcohol, a monomer not normally associated with the lignin biosynthetic pathway, is the major component of the mutant's lignin, accounting for ~30% (vs. ~3% in normal pine) of the units. The level of aldehydes, including new 2-methoxybenzaldehydes, is also elevated. The mutant pines grew normally indicating that, even within a species, extensive variation in lignin composition need not disrupt lignin's essential functions.
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