Auxin response factor 3 (EcARF3) regulates ethylene and ABA biosynthesis and is involved in resistance to synthetic auxin herbicides in Echinochloa crus-galli.

The various components of the auxin signal transduction pathways, including auxin receptors, signal transduction processes, and physiological reactions (such as the overproduction of ethylene and abscisic acid, ABA), contribute to weed resistance to synthetic auxin herbicides. Auxin receptors and their physiological reactions have been well documented; however, research on signal transduction processes associated with herbicide resistance remains limited. In this study, we identified the candidate gene EcARF3, a transcription factor that is upregulated following treatment with florpyrauxifen-benzyl in the susceptible (S) population of Echinochloa crus-galli, whereas its expression remained relatively unchanged in the resistant (R) population. Additionally, key genes in ethylene and ABA biosynthesis, EcACS-like and EcNCED5, were similarly induced and upregulated by florpyrauxifen-benzyl in the S population. Furthermore, protein-DNA binding assays demonstrated that EcARF3 directly binds to the promoters of EcACS-like and EcNCED5, activating their expression. CRISPR-Cas9-mediated knockout of the rice ARF3 ortholog decreased sensitivity to florpyrauxifen-benzyl and quinclorac, whereas overexpression increased it. Moreover, OsARF3 directly binds to the AuxRE element in OsACS7, OsACS7-like, and OsNCED5 promoters, activating their expression, and regulating ethylene and ABA biosynthesis in rice. The role of the ARF3 transcription factor in auxin signal transduction pathways provides new insights into resistance to synthetic auxin herbicide.