title: Mutant analysis in Arabidopsis provides insight into the molecular mode of action of the auxinic herbicide dicamba.
abstract: Herbicides that mimic the natural auxin indole-3-acetic acid are widely used in weed control. One common auxin-like herbicide is dicamba, but despite its wide use, plant gene responses to dicamba have never been extensively studied. To further understand dicamba's mode of action, we utilized Arabidopsis auxin-insensitive mutants and compared their sensitivity to dicamba and the widely-studied auxinic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The mutant axr4-2, which has disrupted auxin transport into cells, was resistant to 2,4-D but susceptible to dicamba. By comparing dicamba resistance in auxin signalling F-box receptor mutants (tir1-1, afb1, afb2, afb3, and afb5), only tir1-1 and afb5 were resistant to dicamba, and this resistance was additive in the double tir1-1/afb5 mutant. Interestingly, tir1-1 but not afb5 was resistant to 2,4-D. Whole genome analysis of dicamba-induced gene expression showed that 10 hours after application, dicamba stimulated many stress-responsive and signalling genes, including those involved in biosynthesis or signalling of auxin, ethylene, and abscisic acid (ABA), with TIR1 and AFB5 required for the dicamba-responsiveness of some genes. Research into dicamba-regulated gene expression and the selectivity of auxin receptors has provided molecular insight into dicamba-regulated signalling and could help in the development of novel herbicide resistance in crop plants.
authors.affiliation: CSIRO Plant Industry, Centre for Environment and Life Sciences, Wembley, Western Australia, Australia.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Gleason
authors.forename: Rhonda C
authors.initials: RC
authors.lastname: Foley
authors.forename: Karam B
authors.initials: KB
authors.lastname: Singh
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D003996:Dicamba / Q000494:pharmacology*; D005030:Ethylenes / Q000494:pharmacology; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D053209:Herbicide Resistance / Q000235:genetics; D006540:Herbicides / Q000494:pharmacology*; D007210:Indoleacetic Acids / Q000494:pharmacology*; D058977:Molecular Sequence Annotation; D009154:Mutation / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D011786:Quality Control; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D029681:Arabidopsis Proteins; D005030:Ethylenes; D006540:Herbicides; D007210:Indoleacetic Acids; D000040:Abscisic Acid; C036216:ethylene; D003996:Dicamba