Journal: Frontiers in Plant Science

Article Title: Metabolic engineering strategies for optimized lignan production in plants

doi: 10.3389/fpls.2026.1827862

Figure Lengend Snippet: Integrated overview of lignan biosynthesis and “Push-Pull-Release” strategies for plant lignan metabolic engineering. (A) Overview of the phenylpropanoid pathway leading to flavonoids, lignin, and lignan precursors. Sequential enzymatic conversions start from L-phenylalanine and branch into flavonoid biosynthesis and monolignol production for lignin monomer (H-, G-, and S-lignin). The principal enzymes and end products depicted are as follows: PAL, phenylalanine ammonia-lyase; C4H, cinnamate 4-hydroxylase; 4CL, 4-coumarate:CoA ligase; CHS, chalcone synthase; HCT, hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyl transferase; C3’H, p -coumaroyl shikimate 3’-hydroxylase; CSE, caffeoyl shikimate esterase; C3H, coumarate 3-hydroxylase; COMT, caffeic acid O-methyltransferase; F5H, ferulate 5-hydroxylase; CCoA-OMT, caffeoyl-CoA O-methyltransferase; CCR, cinnamoyl-CoA reductase; CAD, cinnamyl alcohol dehydrogenase; LAC, laccase; PRX, peroxidase; H-lignin, hydroxyphenyl-lignin; G-lignin, guaiacyl lignin; S-lignin, syringyl-lignin. The pathway also highlights interconnections leading to lignan biosynthesis. Enzyme names are shown at each reaction step, and the main product classes are indicated at pathway termini. (B) Chemical structures of monolignol precursor (coniferyl alcohol) and representative lignans derived from phenylpropanoid pathway. (C) Biosynthetic pathway from coniferyl alcohol to sesamin and podophyllotoxin derivatives. This panel illustrates the enzymatic conversion steps starting from coniferyl alcohol as the precursor of lignan biosynthesis. Key enzymes and their full names are as follows: DIR, dirigent protein; PLR, pinoresinol-lariciresinol reductase; SDH, secoisolariciresinol dehydrogenase; CYP81Q1, (+)-piperitol/(+)-sesamin synthase; CYP719A23, (–)-pluviatolide synthase; OMT3, (–)-pluviatolide-O-methyltransferase; CYP71CU1, (–)-5’-desmethoxy-yatein hydroxylase; OMT1, (–)-5’-desmethyl-yatein O-methyltransferase; 2-ODD, 2-oxoglutarate/Fe(II)-dependent dioxygenase; CYP82D61, (–)-deoxypodophyllotoxin 4-hydroxylase; CYP71BE54, (–)-4’-desmethyl-deoxypodophyllotoxin hydroxylase. Each step highlights the enzyme responsible for the specific biochemical reaction ( Gasper et al., 2016 ; ; Yao et al., 2021 ). (D) Schematic representation of the “Push-Pull-Release” framework for lignan metabolic engineering. “Push” promotes precursor supply, “Pull” redirects flux by blocking competing pathways, and “Release” removes negative regulators to relieve pathway repression. These strategies are linked with synthetic biology tools for modular assembly, multiplex CRISPR, and spatiotemporal control to support lignan production and plant fitness (See Table 1 for a comparative overview of major engineering strategies and their risks and considerations).

Article Snippet: Caffeoyl-CoA O-methyltransferase ( CCoA-OMT ) downregulation in alfalfa ( Medicago sativa ) redirected flux toward the isoflavonoid pathway, thereby improving resistance to F. oxysporum ( ).

Techniques: Derivative Assay, Blocking Assay, Multiplex Assay, CRISPR, Control