Competitive inhibitor of the HD-ZIPIII transcription factors in shoot apical meristem (SAM) development (Probable). Acts by forming non-functional heterodimers (Probable). Part of a negative feedback loop (Probable). Essential for proper functioning of stem cells in the SAM (PubMed:18408069). Interacts with REV. Up-regulated in response to increased HD-ZIPIII activity (PubMed:18055602). Up-regulated by REV (PubMed:22781836). Zpr3 and zpr4 double mutants exhibit homeotic transformation and ectopic meristem activity. Extended C-terminus.