Transport inhibitor response 1 receptor (TIR1)

The Transport inhibitor response 1 receptor (TIR1) is the principal and best-characterized auxin receptor in plants, functioning as an F-box protein subunit in the SCF^TIR1^ ubiquitin ligase complex. Auxin perception at TIR1 is unique—auxin itself binds at TIR1 and acts as a molecular bridge, facilitating the interaction between TIR1 and Aux/IAA transcriptional repressors. This binding leads to ubiquitination and degradation of Aux/IAA proteins, releasing repression of auxin response factors (ARFs) and triggering auxin-responsive gene expression. This pathway underlies numerous developmental processes in higher plants such as cell elongation, organ patterning, and tropic growth responses. TIR1, along with related AFB proteins, forms the core nuclear machinery for auxin signaling in plant biology.

Other names

TIR1Transport inhibitor response 1TIR1/AFB (includes related proteins such as Auxin signaling F-box proteins, AFB1–AFB5)Auxin receptorF-box auxin receptor

Synthetic and natural auxins bind to TIR1, increasing the affinity for Aux/IAA repressor proteins. Auxin acts as a "molecular glue," stabilizing the interaction between TIR1 and Aux/IAA proteins. When bound, TIR1 promotes ubiquitination and subsequent proteasomal degradation of Aux/IAA repressors, derepressing auxin response genes.