Extrinsic (non-cell-autonomous) cues often provide important inputs into cell division and cell fate determination during plant development. As putative transmembrane receptors, leucine-rich repeat receptor-like kinases (LRR-RLKs) are implicated in intercellular signaling and several have known roles in developmental patterning. However, the majority of these proteins remain uncharacterized. We recently reported the unusual accumulation pattern of an LRR-RLK named INFLORESCENCE AND ROOT APICES RECEPTOR KINASE (IRK) in root cell types. IRK-GFP is localized to the outer (lateral) polar domain in endodermal cells; yet, in other cell types, it is localized to another polar domain or is nonpolar. Our results suggest IRK localization is informed by adjacent cell types. Polar localization among LRR-RLKs is rare with very few examples in Arabidopsis. To determine whether polar localization was a conserved feature of IRK-related proteins, we examined localization of these proteins upon endogenous and ectopic expression. Among those examined most localized similarly to IRK, but others showed polar accumulation patterns distinct from IRK. Thus IRK-related proteins are polarized and also reveal novel patterns of polar accumulation in root cells. The discovery of novel polar accumulation patterns has important implications for plant cell biology and the role of cell polarity in root development. Furthermore, polarized RLKs may be more common than we currently understand based on existing literature.
