Transcription factor required for normal cell differentiation. Positively regulates LATERAL ORGAN BOUNDARIES (LOB) within the shoot apex, and the class III HD-ZIP genes REV, PHB, and PHV. Interacts directly with ASYMMETRIC LEAVES 2 (LBD6/AS2) to repress the knox homeobox genes BP/KNAT1, KNAT2, and KNAT6 and the abaxial determinants ARF3/ETT, KAN2 and YAB5. May act in parallel with the RDR6-SGS3-AGO7 pathway, an endogenous RNA silencing pathway, to regulate the leaf morphogenesis (PubMed:11076771, PubMed:11140682, PubMed:11882937, PubMed:12750468, PubMed:16006579, PubMed:16699177, PubMed:17395603, PubMed:17559509, PubMed:23271976). Binds directly to KNAT1, KNAT2, and KNATM chromatin, regulating leaf development (PubMed:23271976). LBD6 is required for this binding (PubMed:23271976). Positive regulator of flowering that binds to the promoter of FT (PubMed:21950734). Regulates FT expression by forming a functional complex with CO (PubMed:21950734). Involved in leaf polarity establishment by functioning cooperatively with NUCL1 to repress abaxial genes ARF3, ARF4, KAN1, KAN2, YAB1 and YAB5, and the knox homeobox genes KNAT1, KNAT2, KNAT6, and STM to promote adaxial development in leaf primordia at shoot apical meristems at high temperatures (PubMed:27334696). Homodimer (PubMed:12750468, PubMed:23271976). Heterodimer with LBD6 (PubMed:23271976). Interacts with LBD6/AS2, HIRA, a probable histone chaperone, and RIK, a predicted RNA binding protein (PubMed:12874130, PubMed:16243907). Part of the AS1 repressor complex composed of AS1, LBD6/AS2 and HDA6 (PubMed:23271976). Interacts with CO (PubMed:21950734). Expressed in roots, stems, leaves, flowers, siliques and in lateral organ promordia (PubMed:17559509). Found in the inner domain between the adaxial and abaxial domains of leaves (PubMed:17559509). Expressed in the phloem tissues of leaves, cotyledons, hypocotyls, and roots (PubMed:21950734). Preferential expression in young and immature plant tissues. In embryos, expressed from the late globular stage onwards. After germination, detected in leaf founder cells and on flowering, in primordia of all floral organs. Circadian-regulation with an afternoon peak in long days and with a broad night peak in short days (PubMed:21950734). Expression of AS1 in stem cells of the shoot apical meristem is prevented by SHOOT MERISTEMLESS (STM). Expression is activated by GTE6 during leaf morphogenesis (PubMed:16166385). A C-terminal domain (252-356) is required for dimerization. Plants with double mutations in this protein and in RH10 or AS2 protein have abaxialized filamentous and trumpet-like leaves at high temperatures. In double mutants, shapes of epidermal cells of the filamentous leaves are simple and rectangular, similar to those of a petiole, but different from those of flat leaves of wild-type plants.