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New Phytol. 2019 Apr;222(1):244-260. doi: 10.1111/nph.15505. Epub 2018 Oct 27.

CAD1 and CCR2 protein complex formation in monolignol biosynthesis in Populus trichocarpa.

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State Key Laboratory of Tree Genetics and Breeding, Chinese Academy of Forestry, Beijing, 100091, China.
Research Institute of Forestry, Chinese Academy of Forestry, Beijing, 100091, China.
Forest Biotechnology Group, Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, 27695, USA.
Department of Biochemistry and DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, University of Wisconsin, Madison, WI, 53726, USA.
State Key Laboratory of Tree Genetics and Breeding, Northeast Forestry University, Harbin, 150040, China.
Department of Forestry, Beihua University, Jilin, 132013, China.
W.M. Keck FT-ICR Mass Spectrometry Laboratory, Department of Chemistry, North Carolina State University, Raleigh, NC, 27695, USA.
Department of Life Sciences, Institute of Plant Biology, College of Life Science, National Taiwan University, Taipei, 10617, Taiwan.


Lignin is the major phenolic polymer in plant secondary cell walls and is polymerized from monomeric subunits, the monolignols. Eleven enzyme families are implicated in monolignol biosynthesis. Here, we studied the functions of members of the cinnamyl alcohol dehydrogenase (CAD) and cinnamoyl-CoA reductase (CCR) families in wood formation in Populus trichocarpa, including the regulatory effects of their transcripts and protein activities on monolignol biosynthesis. Enzyme activity assays from stem-differentiating xylem (SDX) proteins showed that RNAi suppression of PtrCAD1 in P. trichocarpa transgenics caused a reduction in SDX CCR activity. RNAi suppression of PtrCCR2, the only CCR member highly expressed in SDX, caused a reciprocal reduction in SDX protein CAD activities. The enzyme assays of mixed and coexpressed recombinant proteins supported physical interactions between PtrCAD1 and PtrCCR2. Biomolecular fluorescence complementation and pull-down/co-immunoprecipitation experiments supported a hypothesis of PtrCAD1/PtrCCR2 heterodimer formation. These results provide evidence for the formation of PtrCAD1/PtrCCR2 protein complexes in monolignol biosynthesis in planta.


Populus trichocarpa ; co-immunoprecipitation; enzyme activity; monolignol biosynthetic pathway; nuclear magnetic resonance (NMR); stem-differentiating xylem protein


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