Homeodomain transcription factor required for meristem growth and early development (PubMed:15753038). Promotes cell proliferation and prevents premature differentiation in meristematic tissues during postembryonic development (PubMed:15753038). Essential for maintaining tissue growth during embryogenesis (PubMed:17706632). May act by repressing TSS to promote meristematic proliferation (PubMed:21185286). Involved in the transcriptional activation of a subset of cytokinin response factors (PubMed:20110319). May act as a negative regulator of cytokinin signaling in the dark (PubMed:21057190). Expressed in the basal cell and later at the boundary between suspensor and proembryo (PubMed:14711878). Expressed at low levels in proliferating tissues post embryonically (PubMed:15753038). Detected in vegetative shoot apical meristem, leaf primordia, floral meristems, emerging floral organs, epidermal layer of the placenta and in the upper portion of the root meristematic zone (PubMed:15753038, PubMed:20110319). First detected in the basal daughter cell of the zygote (PubMed:14711878). Unlike WOX2 and WOX8, it is not expressed in the egg cell or the zygote (PubMed:14711878). During two subsequent rounds of transverse cell divisions, it is restricted to the hypophysis (PubMed:14711878). At the 8-cell stage, it expands into the central domain of the embryo, in addition to weakening in the hypophysis (PubMed:14711878). After protoderm formation, expression in the central embryo domain is restricted to the protodermal cells and also disappears from the hypophyseal cell (PubMed:14711878). In subsequent stages, a ring of expression remains at the presumptive boundary between root and hypocotyl, at about the same position as WOX2 expression in heart stage embryos (PubMed:14711878). In addition to its embryonic expression, it is expressed postembryonically in the epidermal cells of the placenta during gynoecium development, but not in the developing ovules (PubMed:14711878). The placental expression disappears soon after fertilization (PubMed:14711878). Expression dynamics require MP and BDL, but not GN activity (PubMed:14711878). Detected as early as the first zygotic division in both the apical and the basal daughter cells (PubMed:17706632). By late globular to early transition stage, the protein is evenly distributed through out the embryo and the suspensor (PubMed:17706632). The basal half of the embryo, especially cells in the protoderm layer, starts to show slightly higher levels of expression by early heart stage (PubMed:17706632). Up-regulated in the zygote after fertilization by the transcription factor WRKY2. Embryonic lethality when homozygous (PubMed:17706632). Reduction in embryonic growth, failure in axillary shoot apical meristem and leaf-primordia initiation and growth, and failure in primary root growth and lateral root initiation when heterozygous (PubMed:15753038, PubMed:17706632). Wox8 and wox9 double mutants are embryo lethal, with embryos disrupted as early as the first cell division in the embryo proper (PubMed:17706632). The seedling growth arrest phenotype of the stip mutants likely resulted from a G2 cell cycle arrest of the meristematic tissue (PubMed:17706632). Exogenous sucrose in the growth medium reactivate the stip meristems by repressing TSS and activating the expression of cell cycle regulators, and thus promoting G2 to M transition in meristematic tissues (PubMed:21185286). Belongs to the WUS homeobox family. Truncated C-terminus.