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ARS Home » Pacific West Area » Logan, Utah » Poisonous Plant Research » Research » Publications at this Location » Publication #189809
Title: Involvement of AtLAC15 in lignin synthesis in seeds and in root elongation of Arabidopsis

Author
item LIANG, MINGXIANG - USU
item DAVIS, ELIZABETH - USU
item Gardner, Dale
item CAI, XIAONING - USU
item WU, YAJUN - USU

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2006
Publication Date: 6/30/2006
Citation: Liang, M., Davis, E., Gardner, D.R., Cai, X., Wu, Y. 2001. Involvement of AtLAC15 in lignin synthesis in seeds and in root elongation of Arabidopsis. Planta.

Interpretive Summary: Lignin is, after cellulose, the second most abundant biopolymer on earth. A great effort has been made to reduce lignin content in plants in order to improve nutrition uptake of feeding animals or make cellulose suitable for biofuel production or paper production in a more environmentally-friendly way. Laccase is believed to be involved in the last step of lignin synthesis. Using approaches in genetics, biochemistry and plant physiology, we demonstrated that AtLAC15, one of the laccases in Arabidopsis thaliana, controls the lignin content in the seeds. A chemical component analysis revealed that the laccase mutant seeds had a 30% reduction in lignin. In addition, we found the mutant seeds had more than a 2-fold increase in proanthocyanidin (PA) or condensed tannin than wild-type seeds. To our knowledge, our study provided the first genetic evidence for laccase in lignin synthesis and also uncovers its new function in PA metabolism. Down-regulation of laccase expression in other seeds can have potential application for producing seeds with less lignin. Over-production of PA in seeds could benefit human health since PA can function as antioxidants.

Technical Abstract: Laccase 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 tests (tt) mutant phenotype. A chemical component analysis revealed that the mutant seeds had a 30% decrease in lignin content and more than a 2-fold increase in proanthocyanidin (PA) or condensed tannin compared with wild-type seeds. The content of anthocyanin remained unchanged. In an in vitro enzyme assay, the developing mutant seeds showed a significant reduction in polymerization activity of coniferyl alcohol in the absence of H2O2. Among the dimmers formed in the in vitro assay using developing wild-type seeds, 20% of the linkages were '-O-4 which resembles the major linkages formed in native lignin. Thus, we identified a new function for AtLAC15, i.e. in lignin synthesis, in addition to a newly reported function for AtLAC15 in PA synthesis (Pourcel et al., 2005). To our knowledge, this is the first genetic evidence for the role of laccase in lignin synthesis. Associated with the change in biochemical composition in the mutant seed coat, changes in seed coat permeability and seed germination were observed.