TIR-only protein RBA1 recognizes a pathogen effector to regulate cell death in Arabidopsis
Marc T Nishimura1,2, Ryan G Anderson3, Karen A Cherkis4
1Department of Biology, University of North Carolina, Chapel Hill, NC 27599; marcusn@colostate.edu dangl@email.unc.edu.
Summary
Plant immune receptors, known as nucleotide-binding site leucine-rich repeat (NLR) proteins, can be truncated. A study found that a TIR-only protein, RBA1, acts as a pathogen sensor, expanding knowledge of plant immunity.
Area of Science:
- Plant molecular biology
- Plant immunity
- Structural biology
Background:
- Plant pathogen detection relies on intracellular nucleotide-binding site leucine-rich repeat (NLR) receptors.
- NLRs typically possess Toll-interleukin receptor (TIR), nucleotide-binding (NB), and leucine-rich repeat (LRR) domains.
- The plant immune system utilizes a limited set of NLRs to recognize diverse pathogens.
Purpose of the Study:
- To investigate the function of RBA1, a novel TIR-only protein, in plant immunity.
- To determine the structural and functional requirements for RBA1 activation by the bacterial effector HopBA1.
- To expand the understanding of NLR receptor architecture and plant immune activation mechanisms.
Main Methods:
- Isolation and characterization of the RBA1 gene.
- Generation of the crystal structure of HopBA1.
- Assays for self-association, co-immunoprecipitation, and RBA1 function.
- Analysis of TIR-TIR dimerization interfaces.
Main Results:
- RBA1, a TIR-only protein lacking canonical NLR domains, triggers cell death in response to HopBA1.
- HopBA1 shares structural similarities with esterases and other known proteins.
- RBA1 function and self-association depend on two TIR-TIR dimerization interfaces, indicating oligomerization is crucial.
Conclusions:
- Truncated NLRs, like RBA1, can function as pathogen sensors.
- Oligomerization mediated by specific TIR-TIR interfaces is essential for RBA1's immune function.
- This discovery broadens the scope of known plant immune receptor architectures and activation mechanisms.
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