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要旨:
Autoimmunity that appears in incompatible hybrids in plants can occur due to epistatic interactions between disease resistance (R) genes from separate lineages. R genes, in many cases, encode nucleotide-binding and leucine-rich repeat (NB-LRR) domain containing proteins, which play a key role in perception and activation of immune responses conferring disease resistance against pathogens. In an incompatible hybrid generated by a cross between the two natural accessions of Arabidopsis thaliana, Uk-3 and Uk-1, both two causal genes were identified to encode NB-LRR proteins - DANGEROUS MIX 1 (DM1) and DANGEROUS MIX 2d (DM2d). In this hybrid, epistatic interaction between DM1 and DM2d results in F1 hybrids suffering from dwarfism, reduced growth rate, and spontaneous cell death in leaves. However, how the NB-LRRs as a pair can trigger the autoimmune responses remains to be investigated. To understand the molecular mechanism of DM1/DM2d dependent cell death signaling, we used the yeast two-hybrid (Y2H) system for interaction assays, and the transient and stable expression of the NB-LRRs in Nicotiana benthamiana and A. thaliana, respectively, for functional assays. By using the Y2H system, we defined minimal interaction domains both for the homotypic interaction of DM1 and heterotypic interaction between DM1 and DM2d, and identified mutations that affect the interactions. Our preliminary data suggests that both physical interactions of NB-LRRs and several critical residues that would affect conformation of the protein contribute to induce the signaling. Further experiments are being carrying out to test a hypothesis of asymmetric contribution of the two NB-LRRS to the signaling by (1) fine-mapping residues of the two proteins that can modulate heterotypic- and/or homotypic- interactions, (2) testing functional contributions of these residues to the signaling, and (3) overlaying the experimental information to natural variants of NB-LRRs in A.thaliana to predict the interaction properties of a certain pair.
