Fig. 1

Putative lignin biosynthesis pathway with identification of species-specific reactions. Generic reactions, mainly from studies in the model dicot Arabidopsis thaliana, are shown in grey. Other enzymatic reactions are color coded based on the plant species where they were documented. Multicolored arrows represent reactions present in more than one species. PAL phenylalanine ammonia-lyase, TAL tyrosine ammonia-lyase, C4H cinnamate 4-hydroxylase, C3H p-coumarate 3-hydroxylase, C3′H p-coumaroyl shikimate 3-hydroxylase, COMT caffeic acid O-methyltransferase, F5H ferulate 5-hydroxylase, 4CL 4-coumarate:CoA ligase, HCT hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyl transferase, CCoAOMT caffeoyl-CoA O-methyltransferase, CCR cinnamoyl-CoA reductase, CAD cinnamyl alcohol dehydrogenase, CSE caffeoyl shikimate esterase. Interestingly, some monocots, such as Brachypodium and maize, do not have CSE ortholog genes. Dashed arrows are currently considered less efficient metabolic reactions in vivo