The overarching goal of GRASP was to identify genes and signals important for grafting and to modify these to improve grafting. In the GRASP project, we used Arabidopsis thaliana to identify multiple genes that were activated early during graft formation and we modified their expression to either improve or inhibit grafting. These included transcription factors such as HCA2, cell wall associated genes such as EXG1, wounding related genes such as PAT1, and auxin related genes such as BDL. We identified a critical role for the plant hormone auxin and an important role for cell wall damage in activating genes important for graft formation. By enhancing cell wall damage, we could improve grafting success rates pointing to a key role for damage perception and healing. We also identified an important role for the vascular cambium in successful graft formation of Arabidopsis. As a second achievement, we have studied grafting in monocots, a group of plants previously thought to be ungraftable. We, along with our collaborators, discovered that grafting monocots using embryonic tissues was key to allowing successful grafts to form. We extended these findings to gymnosperms and discovered that grafting with very young conifer trees was highly efficient and allowed spruce and pine trees to be successfully grafted together, something not possible with conventional grafting techniques. Thus, grafting with different tissues types and different tissue ages was key to improving success rates. Finally, we have looked at the role of external cues in grafting success. Using grafting in Arabidopsis and a commercially relevant species, tomato, we found that grafting could be enhanced by elevating temperatures during healing. This enhancement was due to temperature sensing in the leaves producing a mobile signal that could enhance healing at the graft junction. In addition, we uncovered that modifying water availability could determine how a tissue modifies it regeneration fates. Finally, we investigated plant-plant interactions beyond grafting and uncovered a role for cell wall modification, nutrients and the hormone cytokinin during the connection of parasitic plants and their host plants. Such knowledge could be important to transfer to plant grafting to improve grafting success rates.
Work from the GRASP project has been widely disseminated at multiple international and national conferences. The project has given rise to 14 publications including four reviews aimed at broadening grafting-related knowledge to the wider scientific community.
