WUSCHEL in the shoot apical meristem: old player, new tricks.

The maintenance of the stem cell niche in the shoot apical meristem, the structure that generates all of the aerial organs of the plant, relies on a canonical feedback loop between WUSCHEL (WUS) and CLAVATA3 (CLV3). WUS is a homeodomain transcription factor expressed in the organizing centre that moves to the central zone to promote stem cell fate. CLV3 is a peptide whose expression is induced by WUS in the central zone and that can move back to the organizing centre to inhibit WUS expression. Within the past 20 years since the initial formulation of the CLV-WUS feedback loop, the mechanisms of stem cell maintenance have been intensively studied and the function of WUS has been redefined. In this review, we highlight the most recent advances in our comprehension of the molecular mechanisms of WUS function, of its interaction with other transcription factors and hormonal signals, and of its connection to environmental signals. Through this, we will show how WUS can integrate both internal and external cues to adapt meristem function to the plant environment.