| The establishment of vein pattern in leaves is a complex process that involves the communication between different cell types. Vascular Highway 1 is a receptor-like kinase with a specific provascular-procambial expression pattern. The nature of the VH1 protein makes it a good starting point to decipher signaling pathways at work during vascular determination and differentiation. Through an interaction cloning screen, I identified proteins that interact strongly in vitro with the kinase domain of VH1. The functional annotation of these candidate partners of VH1 points to three main routes for VH1 signaling: proteasome, vesicle traffic and signaling pathway. I studied further two interaction candidates belonging to the latter group: VIT, for VH1-interacting tetratricopeptide-containing protein, and VIK, for VH1-interacting kinase. Both of them carry a scaffolding domain that interacts with the intracellular portion of VH1, making them potential bridges between the upstream receptor and downstream effectors of the pathway. To further sustain this hypothesis, VIT shares four interaction partners with VH1.;vit mutations lead to altered venation patterns in cotyledons and primary leaves. vit expression is under the control of auxin and brassinosteroids and insertion lines in this gene display alter sensitivity to both hormones suggesting a role for VIT in the previously observed link between hormone signaling and vein patterning. The VIT expression pattern visualized with GUS reporter lines suggests a close association with developing veins in foliar organs. VIT function is partially masked by its homologous protein, VITL, based on a partial characterization of vit vitl double mutants.;Based on laser capture microdissection of different leaf vascular and non-vascular cell types, I found that VIK expression is vascular specific in expanding leaves. The available insertion line in vik does not display any alteration in vein pattern in foliar organs. However, it exhibits an altered response to auxin, NPA and brassinosteroids.;Together these data shed light on the downstream components of VH1 signaling, and provide a basis for further characterization of these pathways. |
