Functional characterization of NtSCL18 knockout reveals its role in tobacco resistance to bacterial wilt

Ralstonia solanacearum , a soil-borne pathogen with global distribution, infects over 310 plant species including economically important crops such as tomato, eggplant, and pepper, causing bacterial wilt and severe agricultural losses. Scarecrow-like protein 18 ( SCL18 ), a member of the GRAS transcription factor family, primarily regulates plant development and signaling. This study explores the molecular mechanism by which NtSCL18 modulates bacterial wilt resistance in tobacco. CRISPR/Cas9-mediated knockout of NtSCL18 in tobacco cultivar K326 was conducted, with disease resistance evaluated through disease index analysis, lignin content determination, and ROS staining. Transcriptome profiling was performed 24 h post-inoculation with R. solanacearum . Results revealed that NtSCL18 knockout mutants significantly enhanced resistance to R. solanacearum 56 and elevated lignin accumulation. Transcriptome analysis identified 833, 1756, and 1693 differentially expressed genes in the three mutants, respectively. The resistance mechanism involved affection of the Pattern-Triggered Immunity and MAPK signaling cascade, synergistic modulation of ethylene and calcium signaling pathways, and peroxidase-mediated lignin monomer synthesis to reinforce cell walls. In conclusion, NtSCL18 acts as a negative immune regulator; its knockout enhances resistance by coordinately affecting these pathways providing a novel target and theoretical foundation for breeding bacterial wilt-resistant tobacco. This demonstrates the potential of NtSCL18 knockout as a disease control strategy. • NtSCL18 localizes to the nucleus and PM of root/stem cells and enhances resistance to BW by suppressing defense pathways. • Knockout of the NtSCL18 gene activates phenylpropanoid biosynthesis and promotes the accumulation of lignin monomers. • NtSCL18 negatively regulates core immune pathways: suppression of PTI, MAPK cascade, and ethylene responses. • NtSCL18 improves pathogen resistance by influencing metabolic reprogramming (peroxidases).