First molecular bases of cytochrome P450-mediated non-target-site resistance to pendimethalin in Solanum nigrum

The emergence of pendimethalin resistance in Chinese Solanum nigrum populations poses a significant threat to cotton production, yet the underlying resistance mechanisms remain unclear. A putative pendimethalin-resistant S. nigrum population (XJ-R) was collected from cotton cultivation areas in Xinjiang Province, China. Whole-plant dose-response bioassay determined that XJ-R exhibited moderate resistance (5.77-fold) relative to the pendimethalin-susceptible populations (XJ-S). Molecular analyses revealed that no mutations or differential expression in the three α-tubulin isoforms were associated with the pendimethalin resistance of XJ-R population. However, liquid chromatography-mass spectrometry (LC-MS) analysis showed that the pendimethalin residues in XJ-R plants were significantly lower than in XJ-S plants. Enzyme inhibition and activities assays indicated that the cytochrome P450-mediated metabolism identified as the predominant resistance mechanism, and antioxidant involvement by glutathione S-transferases may play a secondary role. Transcriptional upregulation of SnCYP706A-1, supported by molecular docking and dynamics simulations demonstrating catalytic competence, as well as functional validation in yeast, implicate it as potentially primary metabolic determinants. This study establishes the first mechanistic framework for pendimethalin resistance in hexaploid S. nigrum, demonstrating NTSR adaptation rather than TSR alterations as the evolutionary driver. These findings underscore the need to re-evaluate dinitroaniline stewardship in polyploid weeds and prioritize P450-based resistance diagnostics.