Molecular analysis of nucleocytoplasmic signaling pathways in plant cellular immunity
Zusammenfassung der Projektergebnisse
Transport of proteins and RNAs between the cytoplasm and the nucleus is mediated through nuclear pore complexes (NPCs) that are composed of nucleoporin (Nup) proteins. The Nup107- 160 complex is the largest subunit of the NPC and one of its members in Arabidopsis, Nup96/MOS3, was identified as an essential component of auto-immune responses caused by the constitutively active TIR-NB-LRR (TNL) Resistance (R) protein variant, snc1. Using a reverse genetics approach we previously found that among eight putative complex members, beside Nup96/MOS3, only plants with defects in Nup160 or Seh1 are impaired in basal resistance. Constitutive resistance in snc1 and immunity mediated by other TNL R proteins also depend on Nup160 and have a partial requirement for Seh1. The aim of this research proposal was to investigate the molecular function of the Nup107-160 nuclear pore sub-complex with regard to its role in plant immunity. Since vertebrate Nup96 was shown to be selectively required for nuclear export of mRNAs encoding immune regulatory proteins, we sought to analyze nucleoporin mutants of the Nup107-160 complex for defects in the export of specific mRNAs required for full expression of basal and TNL-type R protein mediated immunity. Our functional analyses revealed that defects in nup160, nup96 and seh1 result in nuclear accumulation of poly(A) mRNA, and, in the case of nup160, reduced nucleocytoplasmic transcript and protein accumulation of EDS1, a key positive regulator of basal and TNL-triggered resistance. Together, our data suggest that both reduced nuclear mRNA export activity and overall reduced EDS1 expression in nup160 affect EDS1-conditioned resistance pathways against the oomycete Hyaloperonospora arabidopsidis and the bacterial pathogen Pseudomonas syringae. Intriguingly, we also uncovered that nup160 and nup96/mos3 are more susceptible to another biotrophic plant pathogen and we could show that this correlates with reduced gene expression of the respective receptor that triggers basal immune responses against this pathogen. Our current research aims to understand how Nup160 and MOS3/Nup96 regulate defense gene expression at the molecular level. In addition, an in silico analysis was conducted as part of the funded project in order to identify defense-related interaction partners of the nuclear protein import receptor MOS6/Importin α3 that is essential for snc1-mediated autoimmunity and basal resistance. This analysis uncovered a TIR-NBS protein as a new component of basal plant immunity that interacts with Importin α3/MOS6, but not with its closest homolog Importin α6. In our current research we investigate the subcellular dynamics of this TIR-NBS protein in response to pathogen attack to test our hypothesis of pathogen-induced relocation from the ER to the nucleus.
Projektbezogene Publikationen (Auswahl)
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(2012). Nucleoporins Nup160 and Seh1 are required for disease resistance in Arabidopsis. Plant Signal Behav 7, 1212-1214
Roth, C. and Wiermer, M.
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(2012). Putative members of the Arabidopsis Nup107-160 nuclear pore sub-complex contribute to pathogen defense. Plant J 70, 796-808
Wiermer, M., Cheng, Y.T., Imkampe, J., Li, M., Wang, D., Lipka, V. and Li, X.
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(2013). Hop-on hop-off: importin-α-guided tours to the nucleus in innate immune signaling. Front Plant Sci 4: 149
Wirthmueller, L., Roth, C., Banfield, M.J. and Wiermer, M.
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(2015). Probing formation of cargo/importin-α transport complexes in plant cells using a pathogen effector. Plant J 81, 40- 52
Wirthmueller, L., Roth, C., Fabro, G., Caillaud, M.C., Rallapalli, G., Asai, S., Sklenar, J., Jones, A.M.E., Wiermer, M., Jones, J.D.G. and Banfield, M.J.
