Symmetry Breaking in Plants: Molecular Mechanisms Regulating Asymmetric Cell Divisions in Arabidopsis

Asymmetric cell division generates cell types with different specialized functions or fates. This type of division is critical to the overall cellular organization and development of manymulticellular organisms. In plants, regulated asymmetric cell divisions are of particular importance because cell migration does not occur. The influence of extrinsic cues on asym-metric cell division in plants is well documented. Recently, candidate intrinsic factors have been identified and links between intrinsic and extrinsic components are beginning to be elucidated. A novel mechanism in breaking symmetry was revealed that involves the move-ment of typically intrinsic factors between plant cells. As we learnmore about the regulation of asymmetric cell divisions in plants, we can begin to reflect on the similarities and differ-ences between the strategies used by plants and animals. Focusing on the underlying mol-ecular mechanisms, this article describes three selected cases of symmetry-breaking events in the model plant Arabidopsis thaliana. These examples occur in early embryogen-esis, stomatal development, and ground tissue formation in the root. Plant cells are surrounded by rigid cell wallsthat prevent cell movement. Precisely oriented cell division is especially importan