Effects of Polychlorinated Biphenyls on Lignin Biosynthesis in Arabidopsis thaliana

Growing bioenergy feedstock plants on contaminated land for the combined benefits of bioenergy production and land remediation is an attractive strategy to increase the cost-efficiency of plant-based biofuel. However, prior research has suggested that toxic stress increases the lignin content in exposed plants, which may affect the biomass digestibility and its conversion into bioethanol. In this study, we have conducted a transcriptomic analysis to determine the effect of a polychlorinated biphenyl (PCB), 2,5-dichlorobiphenyl (2,5-DCB), and its hydroxylated derivative, 4'-hydroxy-2,5-dichlorobiphenyl (4'-OH-2,5-DCB), on lignin biosynthesis in the model plant, Arabidopsis thaliana. Both 2,5-DCB and 4'- OH-2,5-DCB induced many genes involved in lignin biosynthesis. A 5.1- and 4.9-fold enrichment of genes involved in the phenylpropanoid pathway were observed in plants exposed to 2,5-DCB and 4'- OH-2,5-DCB, respectively. The upregulated expression of peroxidase, glutathione S-transferase, and glycosyltransferase genes also suggested an activation of the metabolism of xenobiotics in the plant tissues. The lignin content in exposed plants was analyzed using Fourier-transformed infrared spectroscopy (FTIR), confirming that exposure to the two compounds significantly increased the lignin content. Our results suggest for the first time that the exposure of plants to persistent organic pollutants (POPs) may cause an increase of lignin biosynthesis.