Periodic Reporting for period 2 - GRASP (Overcoming plant graft incompatibility by modifying signalling and perception)
Periodo di rendicontazione: 2021-02-01 al 2022-07-31
For millennia people have cut and joined plants together through a process known as plant grafting. By joining plants, people can combine the best properties of each plant, 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. The 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 this project is to understand how plants successfully graft and to use this information to overcome graft incompatibility. The project aims to identify genes and signals that are important for graft formation and to modify these so that grafting success rates improve and a wider range of species can be grafted.
The overarching goal of GRASP is to identify genes and signals important for grafting and to modify these to improve grafting. To date, we have identified multiple genes that are activated early during graft formation and modified their expression to either improve or inhibit grafting. We have 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 can improve grafting success rates pointing to a key role for damage perception and healing. 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 sufficient to allow successful grafts to form. Thus, grafting with different tissues types and different tissue ages was key to improving success rates. Finally, we have looked at grafting in a commercially relevant species, tomato, and found that grafting could be enhanced by elevating temperatures during healing. This enhancement occurred in other grafted plant species and was due to temperature sensing in the leaves producing a mobile signal that could enhance healing at the graft junction. Thus, techniques such as using younger tissues and elevating temperatures could present important tools for enhancing our ability to graft.
Given our progress so far, we anticipate that by the end of the project we will have made major advances in our understanding of how plants graft and the early stages of successful graft formation. Up to now, very few genes are known to be important for grafting but we have identified multiple new regulators that we will characterise in detail. We are focusing on identifying how such genes can act as sensors of successful graft formation and what activates these genes. We are furthermore generating transgenic plants with these regulators modified to test whether we can improve graft formation and overcome graft failure. As an additional objective, we have identified chemicals that improve graft formation rates and that can also increase the rate of vascular formation in plants. We will characterise how such chemicals are working since they could be invaluable for improving graft formation. We will test these chemicals in various species and also in incompatible grafts for their effects on grafting success. Finally, we are identifying genes expressed in common between a variety of grafted species to identify core regulators of the grafting process and will test whether such regulators are affected in incompatible grafts. Altogether, our future experiments will provide an in-depth understanding of plant grafting that we can use to improve grafting in agriculture and horticulture.