HaLAC15, a laccase gene from Haloxylon ammodendron, enhances plant tolerance to pollutants via lignification and substrate degradation

Haloxylon ammodendron, a drought- and salt-tolerant desert shrub, is a valuable plant resource in arid ecosystems. Laccase plays a crucial role in lignin biosynthesis and adaptation of plants to abiotic stress, including heavy metals and organic pollutants; however, the specific functions of laccase genes in the highly stress-tolerant H. ammodendron remain largely unexplored. Therefore, this study focused on a novel laccase gene, HaLAC15, cloned from H. ammodendron, to investigate its role in mitigating the effects of copper (CuSO₄), phenolic acids (sinapic acid, syringic acid, vanillic acid), and 2,4,5-trichlorophenol (TCP) stress. The results indicated that HaLAC15 encoded a secreted laccase protein. Overexpression of HaLAC15 in Arabidopsis enhanced growth and water status under CuSO₄ stress. This improvement was associated with increased activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as reduced accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), thereby indicating a protective effect against oxidative damage and membrane lipid peroxidation. Furthermore, HaLAC15 overexpression increased lignin accumulation in roots, potentially limiting Cu^2 + uptake and translocation. Mg, Mn, and Fe transport coefficients were also higher in HaLAC15-overexpressing lines. HaLAC15 overexpression conferred increased tolerance to phenolic acids, likely due to enhanced sinapic acid and syringic acid degradation. Overexpression of HaLAC15 also exhibited improved growth under TCP stress. Overall, these findings highlight the potential of HaLAC15 in enhancing plant stress resistance to Cu²⁺, phenolic acids and TCP, and its possible application in phytoremediation strategies for contaminated soils.