Localised laccase activity modulates distribution of lignin polymers in gymnosperm compression wood

Abstract

Summary The woody stems of coniferous gymnosperms produce specialised compression wood to adjust the stem growth orientation in response to gravitropic stimulation. During this process, tracheids develop a compression‐wood‐specific S2L cell wall layer with lignins highly enriched with p‐hydroxyphenyl (H)‐type units derived from H‐type monolignol, whereas lignins produced in the cell walls of normal wood tracheids are exclusively composed of guaiacyl (G)‐type units from G‐type monolignol with a trace amount of H‐type units. We show that laccases, a class of lignin polymerisation enzymes, play a crucial role in the spatially organised polymerisation of H‐type and G‐type monolignols during compression wood formation in Japanese cypress (Chamaecyparis obtusa). We performed a series of chemical‐probe‐aided imaging analysis on C. obtusa compression wood cell walls, together with gene expression, protein localisation and enzymatic assays of C. obtusa laccases. Our data indicated that CoLac1 and CoLac3 with differential oxidation activities towards H‐type and G‐type monolignols were precisely localised to distinct cell wall layers in which H‐type and G‐type lignin units were preferentially produced during the development of compression wood tracheids. We propose that, not only the spatial localisation of laccases, but also their biochemical characteristics dictate the spatial patterning of lignin polymerisation in gymnosperm compression wood.

Phenoloxidases in Plants—How Structural Diversity Enables Functional Specificity

“…The cluster with LAC paralogs known to oxidise flavonoids had the smallest binding pockets with moderate (AtLAC15) to minimal (ADE/LAC) compactness and pocket mouth areas (Figure 7E). Another cluster grouped paralogs pivotal for vascular lignification (AtLAC4 and AtLAC11) as well as CoLAC1 shown to preferentially oxidise lignin hydroxyphenyl (H) residue precursors of lignin (Hiraide et al, 2021). This group presented intermediate sized binding pockets of generally low compactness gated by mostly small mouth area (Figure 7E).…”

“…Other LAC paralogs such as AtLAC1, 3, 5, and 13 also specifically accumulate in the casparian strip of endodermal cells (Rojas-Murcia et al, 2020). In Chamaecyparis obtusa, CoLAC1 and CoLAC3 were respectively localised in the inner and outer S2 layers of tracheid compression wood (Hiraide et al, 2021). Beside cell wall localisation, LACs can be targeted to vacuoles in litchi (Fang et al, 2015), to the cytoplasm in hairy roots of Brassica juncea (Telke et al, 2011), but are also predicted to mitochondria in Pinus taeda, Oryza sativa, and Gossypium spp.…”

“…The distinction between constitutive and inducible phenoloxidases, generally defined at the transcriptional level, provides long-term and shortterm responses respectively. When considering lignin formation for example, the function(s) of phenoloxidases will either be constitutive during growth (formation of vascular tissues- Zhao et al, 2013), inducible for growth under constraints (altered by gravity in reaction wood- Hiraide et al, 2021) or induced during biotic stress response (bacterial infection in leaves- Lee et al, 2019). We can subcategorise constitutive phenoloxidases into "in action" or "in waiting, " as phenoloxidases can be regulated by proteolytic activation and/or substrate availability.…”

Phylogenetic Occurrence of the Phenylpropanoid Pathway and Lignin Biosynthesis in Plants

“…Gymnosperms also produce a compression layer within xylem that enriched in H-lignin in tracheid. A recent study showed that spatial patterning of H-and G-lignin during wood formation is related to different localizations and enzyme activities of lignin polymerization enzymes, laccases (Hiraide et al, 2021). Interestingly, some gymnosperm species, such as Gentales, can also synthesize S-lignin (Renault et al, 2019).…”

Plant biomechanics and resilience to environmental changes are controlled by specific lignin chemistries in each vascular cell type and morphotype

“…Due to the low spatial resolution, standard lignin analyses have led to consider lignin polymerisation as a random process only regulated by monomer supply (Barros et al 2015). However, recent works challenged this model by showing that lignification is a genetically controlled process regulating the amounts, linkages and composition of lignin in each cell type and their different cell wall layers Blaschek, Champagne, et al 2020;Yamamoto et al 2020;Hiraide et al 2021). Indeed, different TE morphotypes have been shown to contain lignins with different amounts and differently positioned G CHO (Blaschek, Champagne, et al 2020;Yamamoto et al 2020).…”