“…An obvious candidate for the agent of this transmission is the microtubule array itself, since it is well-known for its ability to self-organise into a wide variety of structures, including aligned cortical arrays with a transverse orientation [98,124,134]. This idea is consistent with the observation that, during protoxylem development, microtubules reorient to a transverse array before apparent band formation [159]. In addition, IQD13, a protein interacting with both microtubules and the plasma membrane, can cause microtubules to act as a "molecular fence" that physically restricts the movement of active ROP and increased expression of this protein results in more flattened spots in metaxylem [154].…”