Involvement of AtLAC15 in lignin synthesis in seeds and in root elongation of Arabidopsis

Abstract

Laccase, EC 1.10.3.2 or p-diphenol:dioxygen oxidoreductase, has been proposed to be involved in lignin synthesis in plants based on its in vitro enzymatic activity and a close correlation with the lignification process in plants. Despite many years of research, genetic evidence for the role of laccase in lignin synthesis is still missing. By screening mutants available for the annotated laccase gene family in Arabidopsis, we identified two mutants for a single laccase gene, AtLAC15 (At5g48100) with a pale brown or yellow seed coat which resembled the transparent testa (tt) mutant phenotype. A chemical component analysis revealed that the mutant seeds had nearly a 30% decrease in extractable lignin content and a 59% increase in soluble proanthocyanidin or condensed tannin compared with wild-type seeds. In an in vitro enzyme assay, the developing mutant seeds showed a significant reduction in polymerization activity of coniferyl alcohol in the absence of H(2)O(2). Among the dimers formed in the in vitro assay using developing wild-type seeds, 23% of the linkages were beta-O-4 which resembles the major linkages formed in native lignin. The evidence strongly supports that AtLAC15 is involved in lignin synthesis in plants. To our knowledge, this is the first genetic evidence for the role of laccase in lignin synthesis. Changes in seed coat permeability, seed germination and root elongation were also observed in the mutant.

LACCASE Is Necessary and Nonredundant with PEROXIDASE for Lignin Polymerization during Vascular Development in Arabidopsis

“…Unlike the high number of peroxidase genes in plant genomes, there are only 17 laccase genes annotated in Arabidopsis (Turlapati et al, 2011). The first genetic evidence of laccase involvement in monolignol polymerization came from analysis of the LAC15-deficient Arabidopsis mutant, which showed significant lignin reduction in the seed coat (Liang et al, 2006). However, because the seed coat is not a highly lignified tissue in Arabidopsis, LAC15 has not been considered to be the major lignin laccase.…”

Transcriptome Sequencing Identifies SPL7-Regulated Copper Acquisition Genes FRO4/FRO5 and the Copper Dependence of Iron Homeostasis in Arabidopsis

“…If the decrease in a ferroxidase activity under Cu deficiency is the cause of the observed impairment in root-to-shoot Fe translocation, then the primary accumulation of Fe will occur in the ferrous oxidation state. This may explain the low intensity of the Perls' stain that is specific for (McCaig et al, 2005;Pourcel et al, 2005;Cai et al, 2006;Liang et al, 2006;Berthet et al, 2011). Direct testing of our current working model will require the identification of the genes that account for the Cu requirement in plant Fe homeostasis.…”

MicroRNA-mediated Systemic Down-regulation of Copper Protein Expression in Response to Low Copper Availability in Arabidopsis

“…In each subgroup some of the genes are expressed in a constitutive fashion, and others are expressed in specific tissues at a particular stage of development (22). Proposed functions of laccases in plants include roles in lignin synthesis (23)(24)(25)(26), wound healing (24), iron acquisition (27), response to stress (28), and the maintenance of cell wall structure and integrity (25). Plantacyanin is a plantspecific protein that contains a single copper ion and belongs to the phytocyanin family of secreted blue copper proteins (29).…”