Fraxinus mandshurica galacturonosyltransferase 1 and 12 play negative roles in cadmium tolerance via cell wall...

Cadmium (Cd) contamination poses critical risks to soil ecosystems, agricultural productivity, and human health. Fraxinus mandshurica, a widely cultivated tree species in landscaping and afforestation, exhibits heightened sensitivity to Cd toxicity. The cell wall, composed of various biological macromolecules, acts as a primary defense mechanism against Cd stress. Galacturonosyltransferase (GAUT) is crucial in cell wall component synthesis and biomass accumulation. However, the involvement of GAUT in metal stress resistance has remained unreported. In this study, FmGAUT1 and FmGAUT12 were obtained from F. mandshurica treated by Cd. Transgenic tobacco overexpressing FmGAUT1 and FmGAUT12 exhibited increased Cd sensitivity, as evidenced by inhibited plant height, reduced fresh weight, and increased reactive oxygen species (ROS) production. In overexpression plants, the cellulose and pectin contents in the cell wall decreased to 52.33 %-55.56 % and 4.30 %-5.17 %, respectively. The reduction in uronic acid, pectin (especially low-methylated pectin), cellulose, and hemicellulose content compromised cell wall binding ability to Cd. Furthermore, the translocation factor and related gene expression levels significantly declined in FmGAUT1 and FmGAUT12 overexpressing lines, resulting in excessive Cd accumulation (1.84-fold and 1.95-fold) in roots. Conversely, silencing FmGAUT1 and FmGAUT12 in F. mandshurica facilitated cell wall remodeling and improved Cd tolerance. These findings reveal the roles of GAUTs in metal stress responses and suggest their potential as targets for genetic improvement strategies to enhance Cd tolerance in plants.