Figure 3.

Biosynthetic map depicting the metabolic relationship between the formation of p-hydroxybenzoate groups (blue) and the monolignols via the shikimate pathway (green), the aromatic amino acid pathway (AAA, yellow), and the phenylpropanoid pathway (purple). p-Coumaroyl-CoA is a common precursor that links syringyl lignin units and p-hydroxybenzoate groups in a metabolic trade-off. A significant negative correlation was observed between cell-wall-bound p-hydroxybenzoate (from 0.9 to 35 mg/g lignin) and syringyl lignin (62.8 to 79.2%) amongst 316 unrelated genotypes of Populus trichocarpa.