RT Journal Article SR Electronic T1 The Arabidopsis Auxin Receptor F-box proteins AFB4 and AFB5 are Required for Response to the Synthetic Auxin Picloram JF bioRxiv FD Cold Spring Harbor Laboratory SP 034652 DO 10.1101/034652 A1 Michael J. Prigge A1 Kathleen Greenham A1 Yi Zhang A1 Aaron Santner A1 Cristina Castillejo A1 Ronan C. O’Malley A1 Joseph R. Ecker A1 Mark Estelle YR 2015 UL http://biorxiv.org/content/early/2015/12/18/034652.abstract AB The plant hormone auxin is perceived by a family of F-box proteins called the TIR1/AFBs. Phylogenetic studies reveal that these proteins fall into four clades in flowering plants called TIR1, AFB2, AFB4, and AFB6 (Parry et al. 2009). Genetic studies indicate that members of the TIR1 and AFB2 groups act as positive regulators of auxin signaling by promoting the degradation of the Aux/IAA transcriptional repressors (Dharmasiri et al. 2005; Parry et al. 2009). In this report, we demonstrate that both AFB4 and AFB5 also function as auxin receptors based on in vitro assays. We also provide genetic evidence that both AFB4 and AFB5 are targets of the picloram family of auxinic herbicides. In contrast to previous studies we find that null afb4 alleles do not exhibit obvious defects in seedling morphology or auxin hypersensitivity. We conclude that AFB4 and AFB5 act in a similar fashion to other members of the family but exhibit a distinct auxin specificity.