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The development of multicellular organisms requires coordinated cell divisions for the production of diverse cell types and body plan elaboration and growth. There are two main types of cell divisions: proliferative or symmetric divisions, which produce more cells of a given type, and formative or asymmetric divisions, which produce cells of different types. Because plant cells are surrounded by cell walls, the orientation of plant cell divisions is particularly important in cell fate specification and tissue or organ morphology. The cellular organization of the Arabidopsis thaliana root makes an excellent tool to study how oriented cell division contributes to tissue patterning during organ development. To understand how division plane orientation in a specific genotype or growth condition may impact organ or tissue development, a detailed characterization of cell division orientation is required. Here we describe a confocal microscopy-based, live imaging method for Arabidopsis root tips to examine the 3D orientations of cell division planes and quantify formative, proliferative, and atypical endodermal cell divisions.

Development of multicellular organisms requires coordination of cell division and differentiation across tissues. In plants, directional signaling, and implicitly cell polarity, is proposed to participate in this coordination; however, mechanistic links between intercellular signaling, cell polarity, and cellular organization remain unclear. Here, we investigate the localization and function of INFLORESCENCE AND ROOT APICES RECEPTOR KINASE (IRK) in root development. We find that IRK-GFP localizes to the outer plasma membrane domain in endodermal cells but localizes to different domains in other cell types. Our results suggest that IRK localization is informed locally by adjacent cell types. irk mutants have excess cell divisions in the ground tissue stem cells and endodermis, indicating IRK functions to maintain tissue organization through inhibition of specific cell divisions. We predict that IRK perceives a directional cue that negatively regulates these cell divisions, thus linking intercellular signaling and cell polarity with the control of oriented cell divisions during development.