Auxin is a key regulator of plant growth and development. It is perceived by a co-receptor system formed by a TIR1/AFB F-box protein and an AUX/IAA transcriptional repressor. TIR1/AFBs act as target receptors of SCF-type E3 ubiquitin ligases. They auxin-dependently bind the AUX/IAA degron, targeting them for ubiquitination followed by proteasomal degradation, leading to auxin response gene activation. Co-receptor combinations can potentially result in an array of auxin sensors impactinggrowth and development responses. In this work, potential sensor combinations and putative features underlying differential auxin sensing were identified. Also, specific auxin sensors TIR1-IAA1 and TIR1-IAA2were biochemically characterized and shown to constitute similar high affinity auxin receptors with similar auxin selectivity. Strikingly, IAA1 and IAA2 exhibited differential auxin-responsive SCFTIR1-dependent ubiquitination in vitro, pointing to functional diversification. For in vivo studies, transgenic plant lines were established and validated. Taken together, this thesis provides important insight on the mechanism of auxin sensing.