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Published on October 29, 2008; 10.1104/pp.108.125765

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Received July 3, 2008
Accepted October 26, 2008

Lignin manipulations in the coniferous gymnosperm Pinus radiata

Armin Wagner *, Lloyd Donaldson , Hoon Kim , Lorelle Phillips , Heather Flint , Diane Steward , Kirk Torr , Gerald Koch , Uwe Schmitt , and John Ralph

Scion, Private Bag 3020, Rotorua, New Zealand; Department of Biochemistry, and the Great Lake Bioenergy Research Center, University of Wisconsin, Madison, Wisconsin 53706, USA; Federal Research Centre for Forestry and Forest Products, Leuschnerstr. 91, 21031 Hamburg, Germany

* Corresponding author; email: armin.wagner{at}scionresearch.com.

Severe suppression of 4-Coumarate-CoA ligase (4CL) in the coniferous gymnosperm Pinus radiata substantially impacted plant phenotype and resulted in dwarfed plants with a ‘bonsai-tree-like’ appearance. Microscopic analyses of stem sections from two-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 NMR studies revealed lignin reductions between 36-50% in the most severely affected transgenic plants. 2D-NMR and Pyrolysis-GC/MS 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 {beta}-aryl ether ({beta}–O–4-unit) and spirodienone ({beta}–1) levels, accompanied by lower phenylcoumaran ({beta}–5), resinol ({beta}–{beta}), and dibenzodioxocin (5–5/{beta}–O–4) levels. A sharp depletion in the level of saturated (dihydroconiferyl alcohol) endgroups was also observed. Severe suppression of 4CL also affected carbohydrate metabolism. Most obvious was an up to ~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.






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