Postembryonic growth and development in higher plants are ultimately reliant on the activity of meristems, where the cells divide frequently to provide source cells for new organs and tissues while in part maintain their pluripotent nature as stem cells. The shoot apical meristem (SAM) is maintained throughout the life of plants and responsible for the development of all areal tissues. In Arabidopsis thaliana, the size of SAM is controlled by a peptide ligand, CLAVATA3 (CLV3). Previously, genetic studies have identified several genes that function downstream of CLV3, many of which, intriguingly, encode receptors. Recently we identified an E3 ubiquitin ligase, PLANT U-BOX 4 (PUB4), as a key regulatory component of root meristem maintenance that functions downstream of an exogenous synthetic CLV3 peptide. Here, we report an additional function of PUB4 in the SAM.