Combining positive and negative regulation of SCF ubiquitin-dependent pathways might be a common mechanism conferring tight control of hormone-mediated responses [19], [34], [39] and [40]. Triple and quadruple mutations in AFBs reduce their interaction with Aux/IAAs and confer defects in auxin-induced gene expression, causing a wide range of auxin-related morphological phenotypes [8]. Single loss-of-function mutation of auxin receptors, except for the tir1 mutation, exhibits normal sensitivity to exogenous auxin, suggesting the TIR1 protein has a critical role in auxin signaling [28]. TIR1 homologs have been identified in plant species other than Arabidopsis, such as Populus, Prunus salicina L., and Solanum lycopersicum); and a wide range of functional identification of TIR1s indicated that they play an important role in plant growth and development [14], [30] and [33].