Required for proliferation and differentiation of shoot stem cells in the shoot apical meristem (SAM), thus determining the appropriate balance between the maintenance of shoot stem cells and their differentiation into other aboveground plant parts via the control of subcellular localization and intercellular trafficking of STM in the shoot apex. Prevents intracellular trafficking of STM to the plasma membrane in cells in the peripheral shoot meristem region thus facilitating STM recycling to the nucleus to maintain stem cells. May function as a signaling molecule by regulating the trafficking of other regulators