Probable transcription factor involved in the regulation of meristem development to promote lateral organ formation. May regulates procambial and vascular tissue formation or maintenance, and vascular development in inflorescence stems. Interacts with ESR1 and ESR2 (PubMed:17376809). Interacts with ZPR3 (PubMed:18408069). A number of isoforms are produced. According to EST sequences. Highly expressed the developing vascular elements and the adaxial portion of cotyledons. Expressed in developing ovules, stamens and carpels. Expressed in procambium and shoot meristem. By auxin. Repressed by miR165 and miR166. Belongs to the HD-ZIP homeobox family. Class III subfamily.