Transcriptional regulator of leaf development. Acts as an adapter-like transcriptional repressor recruiting TPL/TPR corepressors to inhibit the CIN-like TCP transcription factors (PubMed:23444332). Interacts with TPL and the TPR corepressors TPR1, TPR2, TPR3, TPR4, and with the TCP transcription factors TCP2, TCP3, TCP4, TCP5, TCP10, TCP13, TCP17 and TCP24 (PubMed:23444332). Interacts with SPL and SPEAR2 (PubMed:25527103). Expressed in shoot apical meristem, cotyledons and leaves. Detected at the leaf margins and in the vascular bundles at the base of the leaves. Contains 1 EAR motif required for the interaction with TPL and TPRs. No visible phenotype, due to the redundancy with SPEAR2/TIE4 and SPEAR4/TIE3. Knock down expression of SPEAR2/TIE4 and SPEAR4/TIE3 by RNAi in a SPEAR3/TIE1 null mutant produces lines displaying epinastic leaves.