LACCASE14 is required for the deposition of guaiacyl lignin and affects cell wall digestibility in poplar

Abstract

Background The recalcitrance of lignocellulosic biomass provided technical and economic challenges in the current biomass conversion processes. Lignin is considered as a crucial recalcitrance component in biomass utilization. An in-depth understanding of lignin biosynthesis can provide clues to overcoming the recalcitrance. Laccases are believed to play a role in the oxidation of lignin monomers, leading to the formation of higher-order lignin. In plants, functions of only a few laccases have been evaluated, so little is known about the effect of laccases on cell wall structure and biomass saccharification. Results In this study, we screened a gain-of-function mutant with a significant increase in lignin content from Arabidopsis mutant lines overexpressing a full-length poplar cDNA library. Further analysis confirmed that a Chinese white poplar (Populus tomentosa) laccase gene PtoLAC14 was inserted into the mutant, and PtoLAC14 could functionally complement the Arabidopsis lac4 mutant. Overexpression of PtoLAC14 promoted the lignification of poplar and reduced the proportion of syringyl/guaiacyl. In contrast, the CRISPR/Cas9-generated mutation of PtLAC14 results in increased the syringyl/guaiacyl ratios, which led to integrated enhancement on biomass enzymatic saccharification. Notably, the recombinant PtoLAC14 protein showed higher oxidized efficiency to coniferyl alcohol (precursor of guaiacyl unit) in vitro. Conclusions This study shows that PtoLAC14 plays an important role in the oxidation of guaiacyl deposition on cell wall. The reduced recalcitrance of the PtoLAC14-KO lines suggests that PtoLAC14 is an elite target for cell wall engineering, and genetic manipulation of this gene will facilitate the utilization of lignocellulose.

Genome-Wide Identification of Switchgrass Laccases Involved in Lignin Biosynthesis and Heavy-Metal Responses

“…The irregular xylem phenotype was observed in the stem of an Arabidopsis lac4 lac17 double mutant with 40% less lignin content [ 9 ]. The phylogenetically related laccase genes in different plant species, including Miscanthus sinensis [ 10 ], Brachypodium distachyon [ 11 ], and Populus tomentosa [ 12 ], were also found to be involved in lignification. More recent research identified two laccase genes from Japanese cypress ( Chamaecyparis obtusa ) with different oxidation activities towards H-type and G-type monolignols, contributing to the precise localization of H-type and G-type lignin in distinct cell-wall layers [ 13 ].…”

Genome-Wide Comprehensive Analysis of PtLACs: Prediction and Verification of the Functional Divergence of Tandem-Duplicated Genes

“…After transferring PtLAC22, PtLAC25, and PtLAC26 genes into lac2, the roots of the transgenic plants grew normally and responded to osmotic stress caused by PEG. The deposition of lignin usually occurs on the secondary cell walls of growing plants [65]. Excessive lignin deposition reduces the diameter of xylem ducts, restricting the transport of water and nutrients [66].…”

The role of JrLACs in the lignification of walnut endocarp

“…Previous studies found that in poplar, PtoLAC14 is mainly expressed in lignified tissues in the vascular bundles, such as the stem xylem, and that the overexpression of PtoLAC14 resulted in smaller cells with secondary wall thickening and an increased lignin content [ 56 ]. In Arabidopsis , AtLAC4 in interfascicular fibers and seed coat columella, AtLAC15 in seed coat cell walls, AtLAC14 in vascular tissues, such as roots, stems, leaves, petals and leaves but not in siliques (the fruit of Arabidopsis ), are uniquely expressed [ 34 ].…”