Abstract
In plants, cell polarity plays key roles in coordinating developmental processes. Despite the characterization of several polarly localized plasma membrane proteins, the mechanisms connecting protein dynamics with cellular functions often remain unclear. Here, we introduce a polarized receptor, KOIN, that restricts cell divisions in the Arabidopsis root meristem. In the endodermis, KOIN polarity is opposite to IRK, a receptor that represses endodermal cell divisions. Their contra-polar localization facilitates dissection of polarity mechanisms and the links between polarity and function. We find that IRK and KOIN are recognized, sorted, and secreted through distinct pathways. IRK extracellular domains determine its polarity and partially rescue the mutant phenotype, whereas KOIN’s extracellular domains are insufficient for polar sorting and function. Endodermal expression of an IRK/KOIN chimera generates non-cell-autonomous misregulation of root cell divisions that impacts patterning. Altogether, we reveal two contrasting mechanisms determining these receptors’ polarity and link their polarity to cell divisions in root tissue patterning.
Highlights
In plants, cell polarity plays key roles in coordinating developmental processes
Analysis of genes expressed downstream of SHORT ROOT (SHR) activation in the ground tissue (GT) led to the identification of INFLORESCENCE AND ROOT APICES RECEPTOR KINASE (IRK) and another LRR–RLK we named KINASE ON THE INSIDE (KOIN), as candidate proteins involved in the regulation of GT cell divisions15,20–22. koin alleles have a larger root meristem with increased stele area and more numerous cells in the longitudinal axis, as measured by cortex cell number and T-junction length, phenotypes consistent with excessive cell divisions (Fig. 1a–c; Supplementary Fig. 1)
Koin roots are larger than wild type (WT) roots in the radial axis, we consistently observe the expected eight GT cells around the stele and no increase in overall root length (Supplementary Fig. 1f–h)
Summary
Cell polarity plays key roles in coordinating developmental processes. Despite the characterization of several polarly localized plasma membrane proteins, the mechanisms connecting protein dynamics with cellular functions often remain unclear. Asymmetric protein distribution along different plasma membrane (PM) domains can be guided by external cues from adjacent or distal cells and may define polar axes of a tissue or organ This coordinated polarity facilitates oriented cell division, developmental patterning, cell growth, long-range signal transduction, and the transport of ions and other molecules[1]. The leucine-rich repeat receptor-like kinase (LRR-RLK) INFLORESCENCE AND ROOT APICES RECEPTOR KINASE (IRK) exhibits polar accumulation to distinct PM domains in different cell types[15] It localizes to the outer PM domain in the endodermis and pericycle and the inner domain in epidermal and cortical cells, with its polar distribution informed locally by adjacent cells. The mechanistic basis for the establishment and maintenance of IRK polarity remains unknown
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