Periodic Reporting for period 4 - GRASP (Overcoming plant graft incompatibility by modifying signalling and perception)
Okres sprawozdawczy: 2024-02-01 do 2024-12-31
For millennia people have cut and joined plants together through a process known as grafting. By joining different plants, people can combine the best properties two plants, for instance, a disease-resistant root with a fruit-productive shoot. Today, grafting is practised widely in agriculture and horticulture to improve yields and disease resistance. However, grafting is limited by the range of plants that can be successfully grafted. Only certain species can be grafted to each other and for many species, grafting does not work even when plants are grafted to themselves. This failure to graft is referred to as graft incompatibility and presents a limiting factor in our ability to graft and our ability to improve yields and disease resistance. Compounding this issue is that our understanding of how plants graft and why certain grafts fail is limited. The goal of the GRASP project was to understand how plants successfully graft and to use this information to overcome graft incompatibility. The GRASP project successfully identified multiple genes important for graft formation whose expression could be modified to enhance or suppress grafting success. It also discovered hormones and compounds that were sufficient to activate genes associated with graft healing, and described environmental conditions that promoted wound healing and graft formation. Finally, the GRASP project focused on improving grafting success and overcoming graft incompatibility. By grafting with embryonic or very young tissues, GRASP developed techniques that could successfully graft monocot for the first time, and could successfully graft distantly related gymnosperms together for the first time. Ultimately, this knowledge will contribute to a better understanding of plant grafting and plant-plant interactions, and have major implications to improve the rates of graft formation and the number of species successfully grafted.
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.
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.
The GRASP project has provided major insights into the mechanism of plant grafting and expanded the range of successfully grafted species. Until recently, very few genes were known to be important for grafting and the GRASP proposal has greatly increased the list of regulators and factors that control successful graft formation. We have identified and characterized several transcription factors that act as recognition sensors for successful graft formation and tissue regeneration. By employing such sensors, we could identify plant hormones and cell wall modifications as important factors for successful grafting. By employing changes in temperature and water availability, we could promote grafting or modify regeneration fates. Major progress has also been made improving grafting success rates in previously ungraftable species, the monocots, and widening our ability to graft gymnosperms. Furthermore, the GRASP project has studied plant-plant interactions revealing how parasitic plants fuse to their hosts to withdraw nutrients. Altogether, the GRASP project provided an in-depth understanding of plant grafting whose findings can now be deployed to improve grafting in agriculture and horticulture.