A Cotton Laccase Confers Disease Resistance Against Verticillium dahliae by Promoting Cell Wall Lignification

Verticillium wilt (VW), caused primarily by Verticillium dahliae, is a significant threat to cotton production. Lignification of the plant cell wall, a defence response triggered by pathogen invasion, is critical for plant resistance to numerous diseases. Laccases are known to participate in the lignification of secondary cell walls, but their role in cotton resistance to V. dahliae is not fully understood. In this study, we identified a cotton laccase gene, GhLAC14-3, that was significantly upregulated during early V. dahliae infection and was closely related to a gene previously reported to respond to V. dahliae infection in Arabidopsis. Silencing of GhLAC14-3 in cotton increased disease susceptibility and reduced lignin deposition and the expression of lignin-related genes. By contrast, overexpression of GhLAC14-3 in transgenic Arabidopsis increased lignin content and the expression of lignin-related genes, thereby enhancing VW resistance. We identified an interaction between GhLAC14-3 and the mitogen-activated protein kinase GhMAPKKK2 at the cell membrane. GhMAPKKK2 expression was also significantly induced by V. dahliae infection in cotton, and its overexpression in Arabidopsis activated multiple key resistance genes, thus improving V. dahliae resistance. Transient co-expression of GhMAPKKK2 and GhLAC14-3 in Nicotiana benthamiana leaves significantly increased lignin content. Conversely, silencing of AtMAPKKK2, the homologue of GhMAPKKK2, in GhLAC14-3-overexpressing Arabidopsis reduced both lignin levels and disease resistance. Our findings suggest that GhLAC14-3 is a promising target for enhancing VW resistance, as its interaction with GhMAPKKK2 at the cell membrane modulates defence-induced lignification.