A receptor kinase complex refines cambium activity in Arabidopsis

The largest reservoir of terrestrial biomass is the wood within plant stems. Consisting of xylem cells, wood is derived from the cambium, a stem cell population that is maintained by non-cell autonomous signalling. The central component of this system is PXY, a receptor protein present on the plasma membrane of cambium cells. Here, we show that PXY protein interacts with a second membrane-localised receptor kinase, ER, to promote cambium fate. Combinatorial mutations between ER, ERL1 and ERL2 and receptor kinases of a second family, PXY, PXL1, and PXL2, show severe cambial defects, but the mechanism underpinning these phenotypes is not known. Here we discovered that PXY and PXL proteins form protein complexes with ER family members. In genetic analyses, plant lines in which PXY signalling was constitutively active had dramatic phenotypic changes that required the presence of ER or ERL2. Our results demonstrate that PXY signalling mediated cambium regulation depends on ER signalling 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 centre of the accumulation of this versatile biomaterial and essential carbon sink.