It's the Pits Cellular shape is tied to the cytoskeleton, with specialized regions of the plasma membrane attracting or repelling microtubules, a process mediated by the microtubule binding protein MIDD1. In plants, individual xylem cells are peppered with open pits that facilitate fluid transport and so Oda and Fukuda (p. 1333 ) studied ROP “Rho family guanosine triphosphatases of plants” proteins from xylem cells to investigate how pits develop. Formation of the pits seems to depend on MIDD1 to destabilize the microtubules at that point. A cascade of ROP proteins establishes the point at which MIDD1 functions, and reverse inhibition of one of the ROP proteins keeps the pit formation focused on a point.