A receptor kinase complex refines cambium activity in Arabidopsis

In plant development, receptor kinases are often active in disparate cell types, with each requiring vastly different signaling outputs. The ERECTA (ER) receptor kinase and its homologs Erecta-Like1 (ERL1) and ERL2 exemplify this pleiotropy. In Arabidopsis, they influence stomatal patterning, shoot meristem function, and vascular cambium activity, among other functions. Such diverse functionality raises the question of how ER signaling can specify distinct cell behaviors. One key mechanism occurs via cell-type specific interactions with coreceptors, ligands, or other proteins that modulate signaling. However, little is known about ER interactors in the vascular cambium, a bifacial stem cell niche that generates phloem and xylem. Combinatorial mutations between ER, ERL1, and ERL2 and receptor kinases of a second family, Phloem Intercalated with Xylem (PXY), PXY-LIKE1 (PXL1), and PXL2, show severe cambial defects, but the mechanism underpinning these phenotypes is not known. Here, we show that PXY and PXL proteins form protein complexes with ER family members. In genetic analyses, plant lines in which PXY signaling was constitutively active had dramatic phenotypic changes that required the presence of ER or ERL2. Our results demonstrate that PXY signaling mediated cambium regulation in part depends on ER signaling and explains ER function in the cambium. Because the cambium produces xylem, which constitutes the wood in vascular plants, our findings position PXY-ER complexes at the center of the accumulation of this versatile biomaterial and essential carbon sink.