Involved in regulation of circadian rhythm and photoperiodic flowering. May play a role in maintenance of circadian amplitude and period length. Is involved in phytochrome B signaling. Stabilizes ADO3 and the circadian photoreceptor ADO1/ZTL. Regulates 'CONSTANS' (CO) in the long-day flowering pathway by modulating the ADO3-dependent protein stability of CDF1 and CDF2, but is not essential to activate CO transcription. Regulates, via the microRNA miR172, a CO-independent pathway that promotes photoperiodic flowering by inducing 'FLOWERING LOCUS T'. Interacts with SPY (PubMed:15155885). Interacts with ADO1 (via N-terminus) and ADO2 (PubMed:17704763). Interacts with ADO3 (via N-terminus) (PubMed:17704763, PubMed:17872410). Interacts (via N-terminus) with CDF1 (PubMed:17872410). Interacts (via N-terminus) with TCP4 (PubMed:28628608). Widely expressed with highest levels in inflorescence apices, young flowers and young siliques. Found at all stages. Expressed with a circadian rhythm with the highest level 10 hours into the light and the lowest level at dawn. The peak of expression in long days is slightly lower, shifted later and the decrease is slower. Belongs to the GIGANTEA family.