PXC2, a polarized receptor kinase, functions to repress ground tissue cell divisions and restrict stele size

ABSTRACT Coordination of cell division and differentiation is critical for tissue patterning during organ development. Directional signaling and cell polarity have important roles in coordination of these processes. For instance, the Arabidopsis receptor-like kinase INFLORESCENCE AND ROOT APICES KINASE (IRK) functions to restrict stele area and repress longitudinal anticlinal divisions (LADs) in the endodermis where it is polarly localized. IRK is closely related to PXY/TDR CORRELATED 2 (PXC2); here, we show that PXC2 exhibits similar polarized accumulation suggesting they have related functions. pxc2 roots have increased stele area and irk pxc2 double mutant roots show increases in stele area and endodermal LADs beyond either single mutant, indicating that polarly localized IRK and PXC2 function redundantly to repress endodermal LADs and stele area. The double mutant also exhibits agravitropic root growth and abnormal cotyledon vein patterning. Manipulation of PIN1 trafficking and (re)localization mechanisms indicate that PXC2 and/or IRK suggest a link to modulation of polar auxin transport. We conclude that IRK and PXC2 have partially redundant functions in the root, but may have independent functions that are tissue-specific. We propose that repression of endodermal LADs and stele area through a PXC2/IRK-mediated, directional signaling pathway is required for normal ground tissue cell divisions, tissue patterning, and growth in Arabidopsis roots.