A Putative Arabidopsis Nucleoporin, AtNUP160, Is Critical for RNA Export and Required for Plant Tolerance to Cold Stress

Abstract

To study the genetic control of plant responses to cold stress, Arabidopsis thaliana mutants were isolated by a screen for mutations that impair cold-induced transcription of the CBF3-LUC reporter gene. We report here the characterization and cloning of a mutated gene, atnup160-1, which causes reduced CBF3-LUC induction under cold stress. atnup160-1 mutant plants display altered cold-responsive gene expression and are sensitive to chilling stress and defective in acquired freezing tolerance. AtNUP160 was isolated through positional cloning and shown to encode a putative homolog of the animal nucleoporin Nup160. In addition to the impaired expression of CBF genes, microarray analysis revealed that a number of other genes important for plant cold tolerance were also affected in the mutants. The atnup160 mutants flower early and show retarded seedling growth, especially at low temperatures. AtNUP160 protein is localized at the nuclear rim, and poly(A)-mRNA in situ hybridization shows that mRNA export is defective in the atnup160-1 mutant plants. Our study suggests that Arabidopsis AtNUP160 is critical for the nucleocytoplasmic transport of mRNAs and that it plays important roles in plant growth and flowering time regulation and is required for cold stress tolerance.In eukaryotic cells, the genome is enclosed within the nucleus. Nucleocytoplasmic transport of macromolecules across the nuclear membrane occurs through channels formed by nuclear pore complexes (NPCs). Embedded in the double-lipid bilayer nuclear envelope, NPCs form a ringlike structure surrounding a central pore that is believed to facilitate the bidirectional transport of RNAs, proteins, and ribonucleoprotein particles and, at the same time, to allow the diffusion of small molecules and ions across the double membrane (reviewed in reference 4). The overall three-dimensional architecture and transport mechanisms seem to be highly conserved from yeasts to mammals. In Saccharomyces cerevisiae, NPCs are constructed from ϳ30 different nucleoporins with a combined mass of ϳ50 MDa (26). The mammalian NPCs are much larger complexes (ϳ120 MDa) composed of ϳ80 different proteins (10). Although the structural organization of NPCs, the transport mechanism across the channels, and the function of individual nucleoporins have been extensively studied in yeast and vertebrates, very little is known about NPCs in plants.Recently, it was reported that the Arabidopsis thaliana proteins MOS3/SAR3 and SAR1 share high sequence similarities with human nucleoporins Nup96 and Nup160, respectively (25, 34). The putative nucleoporin MOS3/SAR3 was localized at the nuclear rim. The studies suggested that nucleocytoplasmic trafficking plays an important role in plant disease resistance, hormone signaling, and development (25,34). In the present report, we provide evidence that Arabidopsis nucleoporin AtNUP160/SAR1 controls nucleocytoplasmic transport of RNAs and plays important roles in seedling growth, flowering time regulation, and cold stress tolerance.Low temperature is one of...

The Nuclear Pore Protein AtTPR Is Required for RNA Homeostasis, Flowering Time, and Auxin Signaling

“…Strong nuclear staining was only observed in the attpr mutant, suggesting that AtTPR is required for nuclear export of polyA RNA. This result is similar to that seen for loss-of-function mutations in two other Arabidopsis nuclear pore proteins, SAR3 and AtNUP160 (Dong et al, 2006), suggesting that these proteins may have roles related to that of AtTPR in nuclear pore function.…”

“…A striking molecular phenotype of attpr mutants is the accumulation of polyadenylated (polyA) transcripts in the nucleus. Interestingly, a similar nuclear accumulation of polyA RNA has been reported for mutants in two other Arabidopsis NPC proteins, SUPPRESSOR OF AUXIN RESISTANCE3 (SAR3) and SAR1, which are orthologs of the human nucleoporins (NUPs) NUP96 and NUP160 (Dong et al, 2006;Parry et al, 2006). Unlike TPR, NUP96/160 are not associated with the nuclear basket, but are part of the NUP107-160 subcomplex and show a symmetrical distribution on both the cytoplasmic and nuclear faces of the NPC (Tran and Wente, 2006).…”

“…For example, HST was identified in a screen for mutants that accelerate the juvenile to adult phase transition (Telfer and Poethig, 1998;Bollman et al, 2003); SAR3 was identified due to an altered auxin response , and SAR1/AtNUP160 has been shown to affect both auxin signaling and response to cold stress (Dong et al, 2006). Despite having been identified from screens for different phenotypes, hst, sar3, and sar1/atnup160 mutants share several common phenotypes with each other and with attpr, including reduced size, reduced fertility, and early flowering.…”

Regulatory mechanisms involved in cold acclimation response: a review

“…In addition to mRNA processing, the control of mRNA export to the cytoplasm is also influential in plant response to low temperature. In this way, the implication of the Arabidopsis nucleoporin AtNUP160 in cold signaling has been described (Dong et al, 2006a). This protein seems to be involved in mRNA export since a null mutation in the corresponding gene causes mRNA accumulation in the nucleus (Dong et al, 2006a).…”

Dynamics of the Plant Nuclear Envelope and 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.…”