Fig. 1
The monolignol pathway in B. distachyon. In this model, two different pools of 4-coumarate are shown, one originating from the PAL + C4H reactions, the other directly from the reaction catalyzed by TAL. The two pools are shown as being in equilibrium, but they may not be equivalent [20]. The reactions of the shikimate shunt involving the forward “HCTFor” and reverse “HCTRev” HCT reactions are shown in green. The direct pathway through the non-esterified hydroxycinnamic acids, involving a soluble 4-coumarate 3-hydroxylase [7] is shown in red. The enzymes shown in bold capitals are: PAL, L-phenylalanine ammonia-lyase; TAL, L-tyrosine ammonia-lyase; C4H, cinnamate 4-hydroxylase; HCT, hydroxycinnamoyl CoA: shikimate/quinate hydroxycinnamoyl transferase; 4CL, 4-coumarate:CoA ligase; C3´H, 4-coumaroyl shikimate 3´-hydroxylase (cytochrome P450); C3H, 4-coumarate 3-hydroxylase (ascorbate peroxidase); F5H, ferulate/coniferaldehyde 5-hydroxylase; CCoAOMT, caffeoyl-CoA 3-O-methyltransferase; COMT, caffeic acid/5-hydroxyconiferaldehyde 3-O-methyltransferase; CCR, cinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase. CSE, caffeoyl shikimate esterase [5], reported to be absent in some grass species [6], is shown with a question mark