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Publikation

Lüdke, D.; Roth, C.; Kamrad, S. A.; Messerschmidt, J.; Hartken, D.; Apel, J.; Hörnich, B. F.; Yan, Q.; Kusch, S.; Klenke, M.; Gunkel, A.; Wirthmüller, L.; Wiermer, M.; Functional requirement of the Arabidopsis importin-α nuclear transport receptor family in autoimmunity mediated by the NLR protein SNC1 Plant J. 105, 994-1009, (2021) DOI: 10.1111/tpj.15082

Functional requirement of the Arabidopsis importin-a nuclear transport receptor familIMPORTIN-α3/MOS6 (MODIFIER OF SNC1, 6) is one of nine importin-α isoforms in Arabidopsis that recruit nuclear localization signal-containing cargo proteins to the nuclear import machinery. IMP-α3/MOS6 is required genetically for full autoimmunity of the nucleotide-binding leucine-rich repeat immune receptor mutant snc1 (suppressor of npr1-1, constitutive 1) and MOS6 also contributes to basal disease resistance. Here, we investigated the contribution of the other importin-α genes to both types of immune responses, and we analyzed potential interactions of all importin-α isoforms with SNC1. By using reverse-genetic analyses in Arabidopsis and protein-protein interaction assays in Nicotiana benthamiana, we provide evidence that among the nine α-importins in Arabidopsis, IMP-α3/MOS6 is the main nuclear transport receptor of SNC1, and that IMP-α3/MOS6 is required selectively for autoimmunity of snc1 and basal resistance to mildly virulent Pseudomonas syringae in Arabidopsis.
Publikation

Noël, L. D.; Cagna, G.; Stuttmann, J.; Wirthmüller, L.; Betsuyaku, S.; Witte, C.-P.; Bhat, R.; Pochon, N.; Colby, T.; Parker, J. E.; Interaction between SGT1 and Cytosolic/Nuclear HSC70 Chaperones Regulates Arabidopsis Immune Responses Plant Cell 19, 4061-4076, (2007) DOI: 10.1105/tpc.107.051896

The conserved eukaryotic protein SGT1 (for Suppressor of G2 allele of skp1) has characteristics of an HSP90 (for heat shock protein 90 kD) cochaperone and in plants regulates hormone responses and Resistance gene–triggered immunity. We affinity-purified SGT1-interacting proteins from Arabidopsis thaliana leaf extracts and identified by mass spectrometry cytosolic heat shock cognate 70 (HSC70) chaperones as the major stable SGT1 interactors. Arabidopsis SGT1a and SGT1b proteins associate with HSC70 in vivo and distribute with HSC70 in the cytosol and nucleus. An intact C-terminal SGT1-specific (SGS) domain that is required for all known SGT1b functions in immunity and development is needed for HSC70 interaction and for the nuclear accumulation of SGT1b. Interaction assays of transiently expressed proteins or their domains in Nicotiana benthamiana point to a role of SGT1 as a HSC70 cofactor. Expression of two HSC70 isoforms is upregulated by pathogen challenge, and while loss of function of individual cytosolic HSC70 genes has no defense phenotype, HSC70-1 overexpression disables resistance to virulent and avirulent pathogens. Moreover, mutations in SGT1b lead to a similar degree of heat shock tolerance as deregulation of HSC70-1. We conclude that an HSC70-SGT1 chaperone complex is important for multiple plant environmental responses and that the evolutionarily conserved SGS domain of SGT1 is a key determinant of the HSC70–SGT1 association.
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