Mutational studies in Aux/IAA protein provides new insights into their contribution to auxin herbicide resistance

Background: Aux/IAA mutations play an important role in mediating resistance to 2,4-D and other auxin herbicides. The Aux/IAA mutations reported so far that confer auxin herbicide resistance are IAA16 in B. scoparia and C. album, IAA2 and IAA34 in S. orientale and IAA20 in S. oleraceus. In this study we investigated the role of the Arabidopsis orthologues of KsIAA16 and SoIAA20, AtIAA16 and AtIAA5, respectively, to investigate whether the resistance phenotypes were maintained. We also investigated the role of deletion lengths and mutation types in IAA2 mediated auxin herbicide resistance. Results: Transgenic Arabidopsis expressing AtIAA16 and SoIAA2 with substitution mutations in the degron had higher tolerance to 2,4-D, dicamba and picloram treatment compared with wild-type (WT) or Arabidopsis expressing SoIAA2S. Transgenic Arabidopsis lines containing a 27 bp deletion in AtIAA5 had higher tolerance to 2,4-D, dicamba and picloram treatment compared with Arabidopsis expressing SoIAA2S. transformed with deletions in SoIAA2 ranging from 9 to 33 bp were all resistant to 2,4-D, dicamba and picloram. Conclusion: All mutations we tested conferred auxin herbicide resistance in Arabidopsis.