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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Suppression of 4-Coumarate-CoA Ligase in the Coniferous Gymnosperm Pinus radiata^1,[W]

Scion, Rotorua 3010, New Zealand (A.W., L.D., L.P., H.F., D.S., K.T.); Department of Biochemistry and the Great Lake Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53706 (H.K., J.R.); and Federal Research Center for Forestry and Forest Products, 21031 Hamburg, Germany (G.K., U.S.)

Severe suppression of 4-coumarate-coenzyme A ligase (4CL) in the coniferous gymnosperm Pinus radiata substantially affected plant phenotype and resulted in dwarfed plants with a "bonsai tree-like" appearance. Microscopic analyses of stem sections from 2-year-old plants revealed substantial morphological changes in both wood and bark tissues. This included the formation of weakly lignified tracheids that displayed signs of collapse and the development of circumferential bands of axial parenchyma. Acetyl bromide-soluble lignin assays and proton nuclear magnetic resonance studies revealed lignin reductions of 36% to 50% in the most severely affected transgenic plants. Two-dimensional nuclear magnetic resonance and pyrolysis-gas chromatography-mass spectrometry studies indicated that lignin reductions were mainly due to depletion of guaiacyl but not p-hydroxyphenyl lignin. 4CL silencing also caused modifications in the lignin interunit linkage distribution, including elevated β-aryl ether (β-O-4 unit) and spirodienone (β-1) levels, accompanied by lower phenylcoumaran (β-5), resinol (β-β), and dibenzodioxocin (5-5/β-O-4) levels. A sharp depletion in the level of saturated (dihydroconiferyl alcohol) end groups was also observed. Severe suppression of 4CL also affected carbohydrate metabolism. Most obvious was an up to approximately 2-fold increase in galactose content in wood from transgenic plants due to increased compression wood formation. The molecular, anatomical, and analytical data verified that the isolated 4CL clone is associated with lignin biosynthesis and illustrated that 4CL silencing leads to complex, often surprising, physiological and morphological changes in P. radiata.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Armin Wagner (armin.wagner{at}scionresearch.com).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.125765

^* Corresponding author; e-mail armin.wagner{at}scionresearch.com.

Received July 3, 2008; accepted October 26, 2008; published October 29, 2008.

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Plant Physiol. 2009 149: 352-353. [Full Text]