A Putative Nucleoporin 96 Is Required for Both Basal Defense and Constitutive Resistance Responses Mediated bysuppressor of npr1-1,constitutive 1 

Abstract

The Arabidopsis thaliana suppressor of npr1-1, constitutive 1 (snc1) mutant contains a gain-of-function mutation in a Toll Interleukin1 receptor-nucleotide binding-Leu-rich repeat–type resistance gene (R-gene), which leads to constitutive activation of disease resistance response against pathogens. In a screen for suppressors of snc1, a recessive mutation, designated mos3 (for modifier of snc1,3), was found to suppress the constitutive pathogenesis-related gene expression and resistance to virulent Pseudomonas syringae maculicola ES4326 and Peronospora parasitica Noco2 in snc1. In addition, mos3 is also compromised in resistance mediated by Resistance to Peronospora parasitica 4 (RPP4), Resistance to Pseudomonas syringae pv maculicola (RPM1), and Resistance to Pseudomonas syringae 4 (RPS4). Single mutant mos3 plants exhibited enhanced disease susceptibility to P. s. pv maculicola ES4326, suggesting that MOS3 is required for basal resistance to pathogens as well. mos3-1 was identified by map-based cloning, and it encodes a protein with high sequence similarity to human nucleoporin 96. Localization of the MOS3-green fluorescent protein fusion to the nuclear envelope further indicates that MOS3 may encode a nucleoporin, suggesting that nuclear and cytoplasmic trafficking plays an important role in both R-gene–mediated and basal disease resistance.

Arabidopsis resistance protein SNC1 activates immune responses through association with a transcriptional corepressor

“…Multiple TIR-NB-LRR R proteins, including nicotiana glutinosa virus resistance protein (N) in tobacco and resistance to Pseudomonas syringae 4 (RPS4) and suppressor of npr1-1, constitutive 1 (SNC1) in Arabidopsis, have been shown to localize to the nucleus, and reduction of the nuclear R protein pool attenuates the activation of downstream defense responses (7-10). These findings are consistent with that the nucleocytoplasmic trafficking machinery is required for R protein-mediated immunity (9,11,12). However, the function of these R proteins in the nucleus and whether they participate directly or indirectly in transcriptional regulation of defense genes is unclear.…”

“…A point mutation in the snc1 mutant leads to auto-activation of the R protein and enhanced disease resistance (14). An snc1 suppressor screen was carried out previously using fast neutron-treated mutant populations to identify components downstream of R proteins (11). The phenotypes of some identified suppressors were relatively weak, and it was difficult to map those mutations.…”

Abscisic Acid Has a Key Role in Modulating Diverse Plant-Pathogen Interactions

“…Genetic dissection of disease resistance in the model plant Arabidopsis (Arabidopsis thaliana) through lossof-function mutagenesis has identified some important components of basal and R-gene-dependent defenses. For example, EDS1, PAD4, and MOS3 are essential for the resistance specified by the subclass of nucleotide-binding site Leu-rich repeat R proteins that contain an N-terminal Toll Interleukin1 receptor domain, and they are also required for basal resistance to virulent pathogens (Dangl and Jones, 2001;Glazebrook, 2001;Zhang and Li, 2005), while NPR1 was shown to mediate SA-dependent defense responses (Dong, 2001). However, many genes are hard to identify by this approach due to lethality or functional redundancy, especially in complex and reiterative signal networks (Dangl and Jones, 2001).…”

Dynamics of the Plant Nuclear Envelope and Nuclear Pore

“…Its cell cycle dynamics include dispersal at metaphase, accumulation around the chromosomes in late anaphase/early telophase, and reestablishment at the NE in late telophase. Nup136 mutants have complex developmental phenotypes reminiscent of other Nup mutants (Zhang and Li, 2005;Parry et al, 2006;Xu et al, 2007b;Zhao and Meier, 2011). Together, Tamura et al (2010) provide a copious amount of new and confirmatory data about the plant NPC that have the potential to spark a much-needed systematic, multiprong functional investigation of the plant nuclear pore.…”

“…In addition, reverse genetic approaches with Nup homologs have been performed (Zhang and Li, 2005;Dong et al, 2006;Kanamori et al, 2006;Jacob et al, 2007;Saito et al, 2007;Wiermer et al, 2007;Xu et al, 2007b;Zhao and Meier, 2011). In general, however, it has proven difficult to assign plant Nup identity solely based on sequence similarity.…”