Plant stem cell populations are maintained by the precise coordination of stem cell division and the rates of cell division and differentiation among stem cell progenitors. In the growing tips of higher plants (shoot apical meristems, SAMs), stem cell daughters produced by infrequent stem cell division in the central zone (CZ) are displaced towards the surrounding peripheral zone (PZ), where they divide faster and their progeny differentiate into leaves or flowers. Now, Venugopala Reddy and co-workers report that the homeodomain transcription factor WUSCHEL (WUS) mediates stem cell homeostasis in Arabidopsis (see ). The researchers use transient manipulation of WUS expression and live imaging to show that elevated WUS levels in the CZ induce CZ expansion and increase PZ cell division rates. Conversely, decreased WUS levels lead to a smaller CZ, reduced PZ cell division rates and increased responsiveness of PZ cells to the plant hormone auxin, which leads to enlarged organ primordia. Thus, by regulating stem cell numbers and growth and differentiation patterns, a single transcription factor robustly mediates plant stem cell homeostasis.
