Model of auxin signalling in A. thaliana , S. moellendorffii and P. patens. (1) In P. patens and S. moellendorffii, N-terminally truncated Q-rich MRs are predicted to dimerise with full length ARFs to mediate transcription in the presence of auxin. In the absence of auxin, Aux/IAAs inhibit this interaction. Dimirization between other canonical ARFs is also possible. (2) A. thaliana, S. moellendorffii and P. patens full-length ARFs have a MR that is not Q-rich, which can dimerize with either truncated regulatory ARFs in an auxin-independent manner (in P. patens and S. moellendorffii), (3) or with Aux/IAAs in an auxin dependent manner (A. thaliana, S. moellendorffii and P. patens). (4) A. thaliana, S. moellendorffii and P. patens C-terminally truncated ARFs mediate transcription in an auxin-independent manner. (5) A. thaliana and S. moellendorffii ARFs with Q-enrichment in their MR. These ARFs directly activate expression of auxin responsive genes. ARF activators also dimerize and potentiate the activation of auxin responsibe genes. These ARFs are regulated by Aux/IAAs in an auxin-dependent manner.