Oriented cell divisions dictate morphogenesis by shaping tissues and organs of multicellular organisms. Oriented cell divisions have profound influence in plants because their cell positions are locked by shared cell walls. A relay of cell divisions involving precise division plane switches determines embryonic body plan, organ layout and organ architecture in plants. Cell division planes in plants are specified by reorganization of premitotic cortical microtubule array and how this occurs is a long-standing key question.My recent results establish, for the first time in plants, an in vivo inducible and traceable, precise 90º cell division plane switch system. With this system I identified a pathway that proceeds from transcriptional activation through a signaling module all the way to the activation of microtubule regulators that orchestrate switches in premitotic microtubule organization and cell division planes. My findings provide a first paradigm in plants of how genetic circuitry patterns cell division planes via feeding onto cellular machinery and pave the way for unraveling mechanistic control of cell division plane switch.By establishing a precise cell division plane switch system I am in a unique position to answer:1. What transcriptional program and molecular players control premitotic microtubule reorganization?2. Which mechanisms switch premitotic microtubule array?3. What influence do identified players and mechanisms have on different types of oriented cell divisions in plants?For this I propose a systematic research plan combining (i) forward genetics and expression profile screens for identifying a suite of microtubule regulators, (ii) state-of-the-art microscopy and modeling approaches for uncovering mechanisms of their actions and (iii) their tissue-specific manipulations to modify plant form.By unraveling players and mechanisms this proposal shall resolve regulation of oriented cell divisions and expand plant engineering toolbox.