Since many sensor NLRs in the NLR network rely on NRCs for immune activation in the Solanaceae, it was hypothesized that pathogens may secrete virulence proteins, known as effectors, to target NRC function. As part of my MSCA fellowship, BoostR, I screened collections of effector proteins from several agronomically important plant pathogens, including bacteria, aphids, nematodes and oomycetes. I identified two effectors that were able to suppress NRC2 and NRC3, but not NRC4 function. These are AVRcap1b from the late blight pathogen, Phytophthora infestans, and SPRYSEC from the potato cyst nematode pathogen, Globodera rostochiensis. While both these effectors suppress NRC2 and NRC3 function, they do so in different ways. SPRYSEC directly binds to NRC2 and NRC3 in planta, while AVRcap1b does not. This suggests that these pathogens use diverse mechanisms to target the NLR network. Further investigation revealed that SPRYSEC targets the NB-ARC domain of NRC2 and NRC3, a region involved in nucleotide binding, NLR activation and mediating conformational changes within the protein. Based on these findings, I co-authored a research perspective in the journal Science (doi: 10.1126/science.aat2623). The paper highlights fundamental concepts of immune receptor networks and the implications these have for breeding crops for disease resistance. To promote the paper, I was involved in creating a YouTube video titled “Plants have an immune system… and it’s complicated” and participated in an interview for the “Talking Biotech” podcast titled “Plant disease networks”. The video is complementary to the Science perspective and together with the podcast allowed us to reach a broad audience. Additionally, I also co-authored a paper that summarizes the current knowledge of the interplay between effectors, their host targets, and their matching immune receptors (doi: 10.1094/MPMI-08-17-0196-FI). Already these papers have impacted ongoing research in the plant-pathogen interaction community.
Finally, I generated and screened NRC chimeras for expanded sensor specificity and evasion of suppression by pathogen effectors. I identified two NRC chimeras that maintained signalling with their NLR sensor counterparts and that evaded suppression by AVRcap1b and SPRYSEC. For a proof of concept, I transformed these chimeras into the model Solanaceae plant, Nicotiana benthamiana. I also plan to transform them into tomato and potato plants to determine their value in breeding for disease resistance. Results from this part of my project was presented in the form of a research lecture at Imperial College London to students of the Masters in Applied Biosciences and Biotechnology course.
Moving forward, I will continue to advance findings from my MSCA project in my host lab. I am working to narrow down the region within the NB-ARC domain targeted by SPRYSEC and plan to confirm the region within SPRYSEC that governs binding to NRC2 and NRC3. I will also explore the potential target of AVRcap1b. Furthermore, I will screen the transformed potato and tomato plants for enhanced resistance to P. infestans and G. rostochiensis to determine their value in breeding programs. Upon completion, I aim to publish two research papers detailing my findings. Moreover, I co-supervise and mentor a PhD student that is studying the biochemical characteristics of AVRcap1b and SPRYSEC, including determining the mechanisms these effectors use to target NRCs.
In addition to the proposed work, I was also the lead author of two review articles: one which describes oomycete species that are current threats (doi:10.1098/rstb.2015.0459) and another which provides an overview on elicitins (doi: 10.1111/nph.14137). These provide a great overview of the molecular interactions between plants and oomycete pathogens, and fall within the broader umbrella of plant pathogen interaction studies.
