Understanding the role of N, a TIR-NB-LRR protein, in plant innate immunity

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Our goal is to understand the molecular mechanisms by which plant resistance (R) proteins mediate innate immune signaling. We will continue to use the interaction between the N resistance gene and tobacco mosaic virus (TMV) as a model system. The N protein is a member of the TIR-NB-LRR family of R proteins and is hypothesized to specifically recognize the 50 kDa helicase domain (TMV-p50) of the TMV replicase protein to trigger induction of innate immune responses. We will use a combination of genetic, molecular, biochemical and cellular approaches to understand the function of N in innate immunity. We will determine how N recognizes TMV-p50. Recent evidence from our laboratory indicates that N and TMV-p50 associate in intact, living tissue in a narrow period over the course of the host-pathogen interaction and resistance. However, this interaction is not direct and may be dependent on an N-TIR interacting protein we call NTH. This suggests that the TIR domain might be involved in TMV recognition. We will therefore determine domain (s) of N responsible for recognition of TMV-p50. Further, we will characterize the role of NTH in mediating the N and TMV-p50 association. To characterize TMV-p50 recognition complex, we will isolate and identify components of N and NTH protein complexes. Recent results from our laboratory indicate that N associates directly with a transcription factor we call TFN5. Thus, N, in addition to being involved in pathogen recognition, may also directly control downstream transcriptional events. We will determine, in vivo, the interaction dynamics of N and TFN5 before and after TMV infection. We will identify and characterize TFN5 targets during the innate immune response. An increasing world population, from 6 to 12 billion, in the next 50 years will create greater demand for food, fiber, fuel and Pharmaceuticals. We therefore need increased knowledge of plant genes in order to manipulate them to engineer improved crops. Worldwide annual losses of crop productivity due to diseases are valued over $100 billion. Therefore, control of pathogen-induced diseases using natural R genes and other cellular genes that function in the resistance signaling pathways may provide tremendous benefits. This manipulation of endogenous genes will have significant positive impact on poorer citizens. It will serve the environment by offering an alternative to pesticide use to prevent diseases and thus health risks.