GSE178241
RECEPTOR LIKE PROTEIN KINASE 2 constrains proximal secondary vein branching in the Arabidopsis thaliana embryo
Over time, plants have evolved flexible self-organizing patterning mechanisms to adapt tissue functionality to continuous organ growth. A clear example of this process is the multicellular organization of vascular cells into narrow and elongated conductive channels in foliar organs of Arabidopsis thaliana such as cotyledons. The establishment of a closed vascular network is achieved through the coordinated specification of newly recruited procambial cells by means of their proliferation and elongation. An important and yet poorly understood component of this process is secondary vein branching; a mechanism employed to extend vascular tissues throughout cotyledon surface. Here we revise the directionality of the formation of vascular tissues in the embryonic cotyledon of Arabidopsis and show that distal veins arise from the bifurcation of cell files contained in the midvein. Instead, proximal veins emerge from the division of provascular cells, a process partially constrained by RECEPTOR LIKE PROTEIN KINASE 2 (RPK2). Utilizing genetic, transcriptomic and live-cell imaging analyses, we show that RPK2 function is antagonized by COTYLEDON VASCULAR PATTERN 2 and its homologous CVP2 LIKE 1. Whilst RPK2 expression at the cotyledon margin prevents the branching of secondary proximal veins, the divergence of the midvein into distal veins appears to be auxin-dependent and follows a distinct regulatory mechanism. Our work supports a model in which RPK2 modulates vascular complexity independently of cell-to-cell auxin-propagation to adapt the spatial configuration of vascular tissues to organ growth. Overall design: 3 samples examined: embryo (torpedo stage) from Arabidopsis thaliana Col0 wild type, cvp2cvl1 double mutant and cvp2cvl1 containing a transgene expressing a artificial miRNA targeting RPK2