Mechanistic insights into molecular interactions between auxin co-receptor TIR1-IAA7 and typical auxin herbicides

Auxin herbicides exert herbicidal effects by over-inducing auxin response in susceptible plants. While TIR1-IAA7 has been confirmed as the co-receptor for 2,4-D, whether other auxin herbicides exhibit similar herbicidal mechanisms remains unclear. This study aimed to explore the molecular interaction mechanism of typical auxin herbicides from different chemical classes with TIR1-IAA7. MCPA, chloramben, quinclorac, and aminocyclopyrachlor exhibited relatively lower docking energies in the molecular docking simulation, and were selected as representative compounds. In vitro 3H-IAA-binding assay and SPR experiments indicated that MCPA and chloramben showed stronger affinities towards TIR1-IAA7, which was further verified by the mutant resistance experiment. Despite weak TIR1-IAA7 affinity, quinclorac and aminocyclopyrachlor were likely to interact with IAA7 and other TIR1/AFB proteins to dysregulate auxin signaling and inhibit photosynthesis. These findings identify TIR1/AFBs-AUX/IAAs as a promising target for novel auxin herbicides, offering insights into optimizing herbicide usage strategies and finding effective solutions to combat herbicide resistance.