Developmental changes in lignin composition are driven by both monolignol supply and laccase specificity.

Area of Science:

• Plant biology
• Biochemistry
• Biomaterials science

Background:

• Lignin composition is crucial for plant cell walls and industrial applications.
• Catechyl (C)-lignin, a caffeyl alcohol homopolymer, has unique properties but its biosynthesis control is unclear.
• The *Cleome hassleriana* seed coat exhibits a developmental switch from guaiacyl (G)-lignin to C-lignin.

Purpose of the Study:

• To elucidate the regulatory mechanisms controlling the shift in lignin composition during seed coat development in *Cleome hassleriana*.
• To understand the roles of substrate availability and enzyme activity in directing monolignol fate towards G- or C-lignin synthesis.

Main Methods:

• Analysis of lignin composition during seed coat development.
• Investigation of monolignol pathway rerouting and substrate accumulation.
• Biochemical assays to assess enzyme kinetics and substrate interactions (e.g., laccase activity).

Main Results:

• Lignin synthesis in *Cleome hassleriana* seed coats switches from G-lignin to C-lignin around 12-14 days after pollination.
• Caffeyl alcohol synthesis is limited before 12 DAP, while coniferyl alcohol accumulates after 14 DAP.
• Caffeyl alcohol was found to non-competitively inhibit coniferyl alcohol oxidation by laccases, potentially limiting coniferyl alcohol's movement to the apoplast.

Conclusions:

• A model is proposed where developmental changes in substrate availability and laccase specificity govern the switch to C-lignin.
• Caffeyl alcohol's inhibitory role on coniferyl alcohol oxidation is key to regulating lignin composition.
• This provides insight into the biosynthesis of C-lignin and its potential applications.