From top to bottom: Exploring receptor pathways in graft compatibility

Grafting is an ancient technique where two plants are physically connected to make a single plant. Grafts between two plants may be compatible, meaning their vasculature reconnects, or incompatible, meaning they fail to connect their vasculature. Tomato-tomato grafts are compatible, while pepper-tomato grafts are generally incompatible, but it is unknown what causes this incompatibility. The cell death seen in tomato-pepper graft junctions, however, is highly reminiscent of a hypersensitive pathogenic programmed cell death (PCD) response. In a hypersensitive response, receptors on the cell membrane perceive ligand signals from pathogens and trigger a signaling cascade, ending with changes in transcription factor (TF) binding, causing expression of pathogenesis-related genes. Pti5 is a known pathogenesis-related TF, which binds to the GCC box in the plant genome and causes the promotion of many pathogenesis-related genes. Using a tomato line with a mutation in Pti5, we can see if a change in the receptor pathway leading up to Pti5 is important in this response through the tomato’s ability to graft to the pepper. Additionally, we are interested to see if this mutation will also destroy the plant’s ability to defend itself from pathogens. Our experiment involves grafting Pti5 mutant tomatoes, its wild-type (WT) background, and pepper plants. Here, we examine graft survival and observe the success of the vasculature reconnection to compare compatibility of wild-type and Pti5 tomato mutants with peppers to reveal whether Pti5 and its associated pathways are involved in graft incompatibility. In addition, we explore possible new techniques for application of ligands at the graft junction.

I am deeply grateful for the opportunity afforded to me here at the Boyce Thompson Institute. This summer has been a transformative experience for me, and one that will surely impact my learning trajectory from here on out. Meeting and learning from the amazing people in the lab of Dr. Margret Frank was invaluable and each and every one of them have uniquely inspired me to further pursue this field of study. My mentor Sam Yanders has been incredible in providing me with an understanding and patient environment to learn, and I have done just that. As a high school student, I entered this program daunted by the complexity of research; however, my knowledge of plant biology has blossomed under the care of Sam and I am deeply grateful for that. Our research into graft compatibility has been both incredibly intriguing and fun, and has led me down the paths of exploring and learning about a variety of topics such as agrobacterium, PtoR transcription factors, and special types of mRNA that I would not have had the chance or thought to learn about prior to this. This experience has made me grow as a curious mind and embolden me to question and learn about new things. Thank you to everyone at the Boyce Thompson Institute and Frank Labs.