Transcription factor movement through plasmodesmata. (a) WUSCHEL (WUS) is expressed in the organizing center, and WUS protein (W) moves into central zone stem cells. In those cells, W activates the expression of CLAVATA3 (CLV3), a small signaling peptide that prevents WUS expression outside the organizing center. New evidence suggests that WUS dimers repress CLV3 expression in the organizing center. (b) SHORTROOT (SHR) is expressed in the stele, where it localizes to both the nucleus and cytoplasm. SHR protein (S) moves into the endodermis, where it activates the expression of SCARECROW (SCR). Physical interaction with SCR sequesters S to the nucleus, preventing further movement.