Controls photoperiodic flowering response. Component of the circadian clock. Expression of several members of the ARR-like family is controlled by circadian rhythm. The particular coordinated sequential expression of APRR9, APRR7, APRR5, APRR3 and APPR1 result to circadian waves that may be at the basis of the endogenous circadian clock. Positive regulator of CCA1 and LHY expression. Interacts with PIF1, PIL2, PIF3, PIF4, PIL5, PIL6, ABI3 (via C-terminus), ADO1/ZTL, ADO2, APRR3 and TCP21/CHE. Both the phosphorylated and the dephosphorylated forms interact with ADO1/ZLT. Expressed in leaves, flowers and siliques. Restricted to the vasculature. Expressed with a circadian rhythm showing a broad peak in the late day and early night. Negatively regulated by LHY and CCA1. The N-terminus (1-243) is required for interactions with ADO1/ZTL and APRR3. Phosphorylated; during the day. Phosphorylation is required for optimal interaction with APRR3. Subject of targeted degradation by the 26S proteasome. ZEITLUPE (ADO1/ZTL) is the F-box protein that associates with the SCF (for Skp/Cullin/F-box) E3 ubiquitin ligase that is responsible for marking APRR1/TOC1 for turnover. CUL1 is the functional cullin for the SCF(ZTL) complex. APRR3 binding competitively inhibits the ADO1/ZTL interaction. Belongs to the ARR-like family. Lacks the phospho-accepting Asp (here Glu-71), present in the receiver domain, which is one of the conserved features of the two-component response regulators (ARRs) family.