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The crystal structure of immune receptor RGA5A_S of resistance protein Pia from rice (Oryza sativa)
Structural highlights
FunctionRGA5R_ORYSJ Disease resistance (R) protein that recognizes the AVR-Pia and AVR1-CO39 effector avirulence proteins from M.oryzae. Resistance proteins guard the plant against pathogens that contain an appropriate avirulence protein via an indirect interaction with this avirulence protein. That triggers a defense system including the hypersensitive response, which restricts the pathogen growth. Contribution of RGA4 is required to recognize the effector avirulence proteins AVR-Pia and AVR1-CO39 from M.oryzae (PubMed:21251109, PubMed:23548743). Acts as a repressor of the RGA4-mediated cell death activation. Upon infection, recognition and binding of the AVR effectors relieve the RGA5-mediated repression and triggers the hypersensitive response (PubMed:25024433). Immune response triggered by the RGA4-RGA5 -mediated recognition of AVR1-CO39 confers resistance to X.oryzae pathovars (PubMed:27289079).[1] [2] [3] [4] Publication Abstract from PubMedThe structurally conserved but sequence-unrelated MAX (Magnaporthe oryzae avirulence and ToxB-like) effectors AVR1-CO39 and AVR-PikD from the blast fungus M. oryzae are recognized by the rice nucleotide-binding domain and leucine-rich repeat proteins (NLRs) RGA5 and Pikp-1, respectively. This involves, in both cases, direct interaction of the effector with a heavy metal-associated (HMA) integrated domain (ID) in the NLR. Here, we solved the crystal structures of a C-terminal fragment of RGA5 carrying the HMA ID (RGA5_S), alone, and in complex with AVR1-CO39 and compared it to the structure of the Pikp1HMA/AVR-PikD complex. In both complexes, HMA ID/MAX effector interactions involve antiparallel alignment of beta-sheets from each partner. However, effector-binding occurs at different surfaces in Pikp1HMA and RGA5HMA, indicating that these interactions evolved independently by convergence of these two MAX effectors to the same type of plant target proteins. Interestingly, the effector-binding surface in RGA5HMA overlaps with the surface that mediates RGA5HMA self-interaction. Mutations in the HMA-binding interface of AVR1-CO39 perturb RGA5HMA-binding, in vitro and in vivo, and affect the recognition of M. oryzae in a rice cultivar containing Pi-CO39 Our study provides detailed insight into the mechanisms of effector recognition by NLRs, which has substantial implications for future engineering of NLRs to expand their recognition specificities. In addition, we propose, as a hypothesis for the understanding of effector diversity, that in the structurally conserved MAX effectors the molecular mechanism of host target protein-binding is conserved rather than the host target proteins themselves. Specific recognition of two MAX effectors by integrated HMA domains in plant immune receptors involves distinct binding surfaces.,Guo L, Cesari S, de Guillen K, Chalvon V, Mammri L, Ma M, Meusnier I, Bonnot F, Padilla A, Peng YL, Liu J, Kroj T Proc Natl Acad Sci U S A. 2018 Nov 6;115(45):11637-11642. doi:, 10.1073/pnas.1810705115. Epub 2018 Oct 24. PMID:30355769[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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