Disruption of LACCASE4 and 17 Results in Tissue-Specific Alterations to Lignification of Arabidopsis thaliana Stems

Abstract

Peroxidases have been shown to be involved in the polymerization of lignin precursors, but it remains unclear whether laccases (EC 1.10.3.2) participate in constitutive lignification. We addressed this issue by studying laccase T-DNA insertion mutants in Arabidopsis thaliana. We identified two genes, LAC4 and LAC17, which are strongly expressed in stems. LAC17 was mainly expressed in the interfascicular fibers, whereas LAC4 was expressed in vascular bundles and interfascicular fibers. We produced two double mutants by crossing the LAC17 (lac17) mutant with two LAC4 mutants (lac4-1 and lac4-2). The single and double mutants grew normally in greenhouse conditions. The single mutants had moderately low lignin levels, whereas the stems of lac4-1 lac17 and lac4-2 lac17 mutants had lignin contents that were 20 and 40% lower than those of the control, respectively. These lower lignin levels resulted in higher saccharification yields. Thioacidolysis revealed that disrupting LAC17 principally affected the deposition of G lignin units in the interfascicular fibers and that complementation of lac17 with LAC17 restored a normal lignin profile. This study provides evidence that both LAC4 and LAC17 contribute to the constitutive lignification of Arabidopsis stems and that LAC17 is involved in the deposition of G lignin units in fibers.

SND1 Transcription Factor-Directed Quantitative Functional Hierarchical Genetic Regulatory Network in Wood Formation in Populus trichocarpa

“…The five Ptr-LACs and Arabidopsis LAC4 are homologs and were shown to control lignin quantity in P. trichocarpa (Lu et al, 2013) and Arabidopsis (Berthet et al, 2011), respectively. At-LAC4 is a predicted direct target of At-MYB46 based on the MYB46-responsive cis-acting binding site (RKTWGGTR) in the At-LAC4 gene promoter.…”

“…The four MYBs include a pair of paralogs, Ptr-MYB002 and Ptr-MYB021 (Li et al, 2012), and two other MYB related TFs (DEG004 and 005). Ptr-MYB002 and Ptr-MYB021 are the two orthologs of Arabidopsis MYB46, predicted to directly regulate several laccase genes that are associated with lignin biosynthesis (Berthet et al, 2011;Kim et al, 2012a).…”

Small Glycosylated Lignin Oligomers Are Stored in Arabidopsis Leaf Vacuoles

“…The other enzymes of the biosynthetic pathway have no particular targeting signal, but immunolocalization has confirmed the cytoplasmic localization for some of them (Takabe et al, 1985;Chen et al, 2000). Once synthesized, monolignols are transported to the cell wall (Alejandro et al, 2012;Liu, 2012) where they are oxidized by peroxidases (Fagerstedt et al, 2010;Lee et al, 2013) and/or laccases (Berthet et al, 2011;Lu et al, 2013;Zhao et al, 2013). The resulting electron-delocalized monolignol radical can couple at several positions with another monolignol radical or, more often, with a radical at the free-phenolic end of the growing polymer.…”

A Key Role for Apoplastic H2O2 in Norway Spruce Phenolic Metabolism

“…Although there is some degree of variation among species in the architecture of the monolignol biosynthetic pathway, it is largely consistent across different plant groups (Mottiar et al, 2016). In Arabidopsis (Arabidopsis thaliana), both laccases and peroxidases are required for monolignol oxidation in lignin polymerization, possibly acting sequentially, and/or in different tissues (Berthet et al, 2011;Lee et al, 2013;Novo-Uzal et al, 2013;Zhao et al, 2013;Barros et al, 2015;Shigeto and Tsutsumi, 2016). In Norway spruce, numerous peroxidase and laccase isoenzymes have been reported in the cell walls of developing xylem and in the culture medium of the ligninforming cell culture utilized in this study (Kärkönen et al, 2002;Fagerstedt et al, 2010;Koutaniemi et al, 2015).…”