Abstract
SCF(TIR1/AFB) auxin signaling pathway regulate the auxin-responsive gene expression. In this pathway, auxin is perceived by TIR1/AFB auxin receptors, leading to the degradation of Aux/IAA repressors mediated by SCF(TIR1/AFB) E3 ubiquitin-ligase. Auxin Binding Protein 1 (ABP1) has been believed to be another auxin receptor. However, the physiological function of ABP1 and its down-stream components have been still unknown. Therefore, ABP1 specific ligand would be useful chemical tool to investigate the function and signaling of ABP1. We designed ABP1 ligand according to the crystal structures of ABP1, and assessed the physiological activity of ABP ligand. The ABP1 ligand promoted the hypocotyl elongation and adventitious root formation in Arabidopsis plant, but the ligand did not activate the DRS-GUS expression under the control of SCF(TIR1/AFB) signals. Additionally, axrl-3 and tirl afb2 mutants were sensitive to the ABP1 ligand and the ligand did not induce the interaction between TIR1 and Aux/IAA. On the contrary, the conditional loss of functional mutant on ABP1 was highly resistant to the ABP1 ligand. These evidences suggest that the ligand would specifically activate ABP1 signals.
