Essential protein required for cell fate determination during embryogenesis (PubMed:15266054). Mediates auxin-dependent coordinated cell-fate specification and patterning in embryos (e.g. cotyledon outgrowth and separation), shoots and roots (e.g. leaf vascular development, cellular patterning and stem cell maintenance in the meristems) (PubMed:19880797, PubMed:20729639). Required for provascular PIN1 expression and region-specific expression of PIN7 in leaf primordia, cell type-specific expression of PIN3, PIN4, and PIN7 in the root, and PIN2 polarity in the root cortex (PubMed:19880797, PubMed:20729639). Accumulates in speckles within the nucleus and the nucleolus. Specifically expressed in developing embryos, leaf primordia, and shoot and root apical meristems. In shoots, expressed in developing leaf primordia and, weakly, in the shoot apical meristem (SAM). First observed throughout young leaf primordia, but, as leaf primordia develop, restricted to the adaxial side of primordia and then toward the basal side. In seeds, present in developing embryos and later in provascular cells of cotyledons at the early stage of vascular differentiation. In roots, accumulates in the root apical meristem (RAM) with weak expression in the quiescent center and columella initials but not in mature root tissues; also expressed during primordial development of lateral roots. Embryo-defective phenotype characterized by size reduction and frequent fusion of cotyledons. Was originally thought to correspond to two different genes At4g13740 and At4g13750. Was originally thought to correspond to two different genes At4g13740 and At4g13750. Was originally thought to correspond to two different genes At4g13740 and At4g13750. Was originally thought to correspond to two different genes At4g13740 and At4g13750.