Title: Beyond single genes: receptor networks underpin plant immunity
Speaker: Prof. Sophien Kamoun, The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom
Date: April 6th, 2018(Friday)
Host PI: Prof. Yoji Kawano
Venue: PSC Auditorium
A fundamental concept in plant pathology is that most plants are actively resistant to most pathogens and pests. Plants fend off their innumerable biotic foes primarily through immune receptors that detect the invading pathogens to trigger a robust immune response. The conceptual basis of such interactions was elegantly articulated by Harold H. Flor, who back in 1942 proposed the hypothesis that single genes in plants and pathogens define the outcome of their interactions. Flor’s gene-for-gene model turned out to be hugely insightful and influential—it has, ever since the mid-twentieth century, helped to guide applied and basic research on disease resistance. However, recent findings are taking the field far beyond the simplified binary view of plant-pathogen interactions. Plants turned out to carry extremely diverse and plastic repertoires of immune receptors that are interconnected in complex ways. Conversely, plant pathogens secrete a diversity of virulence proteins and metabolites known as effectors, and pathogen genomics revealed hundreds of effector genes in many species. These effectors have evidently evolved to favor pathogen infection and spread, but a subset of them inadvertently activate plant immune receptors. The emerging paradigm is that dynamic webs of genetic and biochemical networks underpin the early stages of plant-pathogen interactions.
Plant immune receptors are classed into cell surface receptors, receptor-like kinases (RLKs) and receptor-like proteins (RLPs), or intracellular receptors of the nucleotide-binding domain and leucine-rich repeat-containing (NLR) family. The network feature of cell surface receptors is well established. Several RLKs, such as BAK1, serve as interconnected crosstalk nodes, reflecting their essential roles in the response to multiple environmental stimuli. Other RLKs stand out as articulation points that may play important roles in maintaining network integrity and ensuring appropriate response modulation. NLR proteins also engage in genetic and biochemical interactions that are more complex than anticipated. Many NLRs, which sense host-translocated pathogen effectors, require other NLR proteins to function, forming connections that vary from NLR pairs to networks. NLR pairs often operate through negative regulation, with the sensor NLR releasing its inhibition of helper NLR autoactivity upon pathogen perception. In asterid plants, NLRs in the NRC network form a complex genetic network that operates against multiple pathogens. The NRC network has evolved from an ancestral NLR pair that expanded to half of all NLRs in some species. In this talk, I will discuss our work on NLR networks and explore the implications of this systems view of plant-pathogen interactions. I postulate that Flor’s intuitive gene-for-gene model is superseded by the systems view that plant immune receptors form networks with complex topology. These networks are defined by the uncoupling of plant pathogen perception from initiation of downstream signaling and immune response. Current work aims at decrypting the biochemical codes that define receptor network wiring. Ultimately, an improved knowledge of plant immune systems would enable optimal use and deployment of immune receptors in agriculture.