Multicellular organisms use asymmetric cell division (ACD) to generate diverse cell types during development. In contrast to the mechanism revealed in animals, our knowledge on plant ACD is limited. Current models focus on the plant-specific microtubular structure, the preprophase band (PPB), in regulating oriented division. However, recent studies suggest a more fundamental role of proteins at the cortical division zone (CDZ), which assemble regardless of the presence or absence of PPBs, during ACD. However, it is unclear how CDZ is formed at a specific cortical domain and how it regulates oriented cytokinesis, which involves rotation or “guidance” of the mitotic apparatus (called phragmoplast). I aim to reveal the molecular mechanism underlying plant ACD, focusing on the assembly and function of the CDZ. Specifically I will: 1. Elucidate the phragmoplast guidance mechanism through advanced imaging and revealing the function of a key kinesin motor at the CDZ. 2. Identify new factors that affect CDZ assembly and phragmoplast guidance. I will use the moss Physcomitrella patens as the model system, which has a short life cycle, simple morphological structures, and efficient genome-editing tools. Both PPB-dependent and -independent asymmetric division take place in moss, which enables the identification of core effectors involved. By combining advanced genetics and high-resolution imaging tools, I will investigate the roles of CDZ in ACD through identifying novel factors upstream of CDZ and dissecting the interplay between CDZ and phragmoplast-involved cytokinesis. In the end, I envision mechanistic comparison with better-studied animal and yeast systems.