The vascular system is important for the transport of nutrients, hormones and water in plants and animals. After damage such as by wounding, strokes or heart attacks, animals have an often limited capacity to reconnect the vascular system. Plants are different, as uniquely, many efficiently reattach and repair wounded or cut vascular strands even after complete severing. This mechanism works both within a plant, but remarkably, cut plants can form vascular connections with different plants of the same species or even different species. The basis for how plants do this is completely unknown, yet it is a property that humans have exploited for thousands of years to graft plants. Grafting is a process whereby different plants are cut, attached and grown as a single plant. It is commonly used in orchards to change the size of trees, used in vineyards to confer disease resistance or used to propagate plants.

The ability of different plant species to connect with each other also has a darker side. Parasitic plants are widespread pathogens that infect crops and greatly diminish agricultural yields. They infect plant roots or shoots by attaching aspects of their vasculature to the host’s vasculature, and use it to draw out nutrients. In a sense, parasitic plants “graft” to their hosts, but remarkably, they can infect a wide range of plants that are completely unrelated to the parasite, something that is not currently possible with traditional plant grafting. How parasitic plants “graft” to plants remains largely unknown.

The goal of our research is to understand how plants repair and connect their vasculature. We are approaching this question through three major goals:

1) How does the plant regenerate a wounded stem? In particular, how does the vasculature connect and how do tissues fuse? What are the contributions of hormones, cell  wall modifications, plasmodesmata and mechanical forces?

2) How does the plant recognise self vs non-self? Is there a defense response at the wound site that contributes to graft incompatibility?  Why do some plants efficiently graft whereas others do not?

3) How do biotic stresses, such as parasitic plant infections, promote tissue fusion and vascular formation between the pathogen and host? Does the mechanism share similarities to wound healing? How does the pathogen overcome self/non-self recognition?

Arabidopsis hypocotyl graft between a plant expressing a green fluorescent protein and a red fluorescent protein