Plant Molecular Biology

, Volume 49, Issue 2, pp 199-214

First online:

The western red cedar (Thuja plicata) 8-8′ DIRIGENT family displays diverse expression patterns and conserved monolignol coupling specificity

  • Myoung K. KimAffiliated withInstitute of Biological Chemistry
  • , Jae-Heung JeonAffiliated withInstitute of Biological Chemistry
  • , Masayuki FujitaAffiliated withInstitute of Biological Chemistry
  • , Laurence B. DavinAffiliated withInstitute of Biological Chemistry
  • , Norman G. LewisAffiliated withInstitute of Biological Chemistry

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The isolation and characterization of a multigene family of the first class of dirigent proteins (namely that mainly involved in 8-8′ coupling leading to (+)-pinoresinol in this case) is reported, this comprising of nine western red cedar (Thuja plicata) DIRIGENT genes (DIR1–9) of 72–99.5% identity to each other. Their corresponding cDNA clones had coding regions for 180–183 amino acids with each having a predicted molecular mass of ca. 20 kDa including the signal peptide. Real time-PCR established that the DIRIGENT isovariants were differentially expressed during growth and development of T. plicata (P<0.05). The phylogenetic relationships and the rates and patterns of nucleotide substitution suggest that the DIRIGENT gene may have evolved via paralogous expansion at an early stage of vascular plant diversification. Thereafter, western red cedar paralogues have maintained an high homogeneity presumably via a concerted evolutionary mode. This, in turn, is assumed to be the driving force for the differential formation of 8-8′-linked pinoresinol derived (poly)lignans in the needles, stems, bark and branches, as well as for massive accumulation of 8-8′-linked plicatic acid-derived (poly)lignans in heartwood.

8-8′ DIRIGENT multigene family lignans and lignins real-time PCR recombinant protein stereoselective phenoxy radical coupling western red cedar (Thuja plicata)