Auxin signaling in the cambium promotes tissue attachment and vascular development during Arabidopsis thaliana graft formation

The remarkable ability of plants to regenerate wounds is exemplified during the process of plant grafting when two plants are cut and joined together to grow as one. During graft healing, damaged tissues attach, cells proliferate and the vasculatures connect to form a graft union. The plant hormone auxin plays a central role and mutants perturbed in auxin response fail to successfully graft. Here, we investigated the role of individual cell types and their response to auxin during Arabidopsis thaliana graft formation. By employing an inducible misexpression system, we blocked auxin response in individual cell types using the bodenlos mutation. We found that auxin signaling in procambial tissues was critical for both successful tissue attachment and also for vascular differentiation. In addition, we found that auxin signaling was required for cell divisions of the procambial cells during graft formation. Loss of function mutants in cambial pathways also perturbed attachment and phloem reconnection. We propose that cambium and procambium are key tissues that allow both tissue attachment and vascular differentiation during successful grafting. Our study thus refines our knowledge of graft development and furthers our understanding of regeneration biology and the function of cambium.