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

Abstract

The factors controlling lignin composition remain unclear. Catechyl (C)–lignin is a homopolymer of caffeyl alcohol with unique properties as a biomaterial and precursor of industrial chemicals. The lignin synthesized in the seed coat of Cleome hassleriana switches from guaiacyl (G)– to C-lignin at around 12 to 14 days after pollination (DAP), associated with a rerouting of the monolignol pathway. Lack of synthesis of caffeyl alcohol limits C-lignin formation before around 12 DAP, but coniferyl alcohol is still synthesized and highly accumulated after 14 DAP. We propose a model in which, during C-lignin biosynthesis, caffeyl alcohol noncompetitively inhibits oxidation of coniferyl alcohol by cell wall laccases, a process that might limit movement of coniferyl alcohol to the apoplast. Developmental changes in both substrate availability and laccase specificity together account for the metabolic fates of G- and C-monolignols in the Cleome seed coat.

Different combinations of laccase paralogs non-redundantly control the lignin amount and composition of specific cell types and cell wall layers in Arabidopsis

“…Our results clearly localised the activity of different LAC paralogs in distinct cell wall layers and cell types, such as LAC12 in the CC of IFs (figures 2, 5). In vitro LAC activity assays using heterologously expressed LACs have moreover yielded unexpected results, with either LACs showing no activity (Sato et al 2001), activities that were at odds with the enzyme’s in vivo effect (He et al 2019), or showing activity only after adding water soluble xylem extracts to the reaction buffer (Zhuo et al 2022). Performing activity assays directly in situ avoids these effects by maintaining the native reaction environment of LACs and provides results that directly reflect the function of the enzyme in planta .…”

“…In fact, different LACs show highly distinct binding pocket and active site topologies, suggesting differences in catalytic efficiency, pH optimum and/or substrate specificity (Blaschek and Pesquet 2021). Indeed, LACs involved in the formation of specialised lignins in seed coats and compression wood were recently shown to exhibit a certain degree of substrate specificity for monomers with different ring substitutions (Wang et al 2020; Hiraide et al 2021; Zhuo et al 2022). The role of LAC specificity in the main developmental lignification of xylem however remains unclear.…”

Multi-omic characterization of bifunctional peroxidase 4-coumarate 3-hydroxylase knockdown in Brachypodium distachyon provides insights into lignin modification-associated pleiotropic effects

“…The substantial decrease in abundance of laccase proteins observed from proteomics measurement in C3H/APX-KD compared to controls suggests that the C3H/APX-KD may have reduced ability to oxidize monolignols, which might contribute to their low total lignin. Besides lignin quantity, lignin composition can also be controlled at the polymerization level ( Tobimatsu and Schuetz, 2019 ; Zhuo et al., 2022 ). Our proteomics and transcriptomics analyses identified several peroxidases co-regulated with C3H/APX.…”

Dual Mechanisms of Coniferyl Alcohol in Phenylpropanoid Pathway Regulation

“…A series of aromatic hydroxylations, O-methylations and side-chain reductions then lead to the formation of the three major lignin monomers (monolignols) p-coumaryl alcohol, coniferyl alcohol (CA) and sinapyl alcohol (Bonawitz and Chapple, 2010). After transport across the plasma membrane, most likely by a passive diffusion mechanism (Perkins et al, 2022;Zhuo et al, 2022), monolignols are oxidatively polymerized by laccases and peroxidases in the apoplastic space (Lee et al, 2013;Zhao et al, 2013).…”

“…It is intuitive that the regulation of lignin biosynthesis might involve sensing of ligninspecific precursors. It was recently shown that CA biosynthesis can be maintained in the absence of guaiacyl or syringyl lignin biosynthesis (Zhuo et al, 2022), suggesting that CA may serve roles beyond simply being a lignin building block. In this study, we explored the function of CA in the regulation of lignin biosynthesis.…”