Figure 1.

Schema of the Proposed Oxidative-Dehydrogenation and Phenoxy-Coupling, and the Reactions Catalyzed by Phenolic O-Methyltransferases.

(A) The active radical intermediates are generated from the monolignol (coniferyl alcohol) by oxidation of its phenol. The phenoxy radicals couple together or, more importantly, with the growing lignin oligomer/polymer yielding units with different interunit linkages in lignins.

(B) The 4-O-methylation of phenylpropenes catalyzed by IEMT.

(C) The engineered monolignol 4-OMT (MOMT) (in gray box); note the structural analogy between the monolignol coniferyl alcohol and the phenylpropene isoeugenol.

[See online article for color version of this figure.]