HAIRY MERISTEM with WUSCHEL confines CLAVATA3 expression to the outer apical meristem layers

Enough but not too many stem cells In the shoot apical meristem of plants, just the right number of stem cells generates a steady supply of cells with which to build differentiated tissues. Too few stem cells, and the plant cannot grow. Too many, and growth runs amok. Zhou et al. analyzed the controls on stem cell proliferation. They found that the HAIRY MERISTEM proteins define a domain within which WUSCHEL (WUS) cannot work, but beyond which WUS is left free to promote stem cell proliferation. Science , this issue p. 502