The shoot apical meristem (SAM) of higher plants contains the stem cell population that contributes to all above-ground organs. During vegetative growth, leaf primordia emerge from the periphery of the SAM, and the SAM transitions to an inflorescence meristem to initiate the reproductive phase. The WUSCHEL transcription factor specifies stem cell fate, and hence controls the size and activity of the SAM. A gene network involving the CLAVATA signalling pathway, the microRNA miR166g and HD-ZIPIII transcription factors is responsible for regulating WUSCHEL levels. On , Leor Eshed Williams and colleagues add another layer to this regulatory system, defining a role for the ERECTA receptor kinase in restricting WUSCHEL expression. Plants overexpressing miR166g and carrying a mutation in ERECTA display a massively enlarged SAM, disrupted phyllotaxis patterns and defects in floral meristem formation. ERECTA acts independently of the CLAVATA system, and although the mechanisms by which it functions are not fully clear, this work adds another important player to the complex regulatory network underlying meristem activity.
