Abstract
The selective trafficking of proteins and RNAs through the nuclear envelope regulates nuclear-cytoplasmic segregation of macromolecules and is mediated by nucleopore complexes (NPCs), which consist of about 400 nucleoporins (Nups) of about 30 types. Extensive studies of nucleoporin function in yeast and vertebrates showed that Nups function in nucleocytoplasmic trafficking and other processes. However, limited studies of plant Nups have identified only a few mutations, which cause pleiotropic phenotypes including reduced growth and early flowering. Here, we describe loss-of-function alleles of Arabidopsis TRANSCURVATA1 (TCU1); these mutations cause increased hypocotyl and petiole length, reticulate and asymmetrically epinastic leaf laminae of reduced size, and early flowering. TCU1 is transcribed in all of the organs and tissues examined, and encodes the putative ortholog of yeast and vertebrate Nup58, a nucleoporin of the Nup62 subcomplex. Nup58 forms the central channel of the NPC and acts directly in translocation of proteins through the nuclear envelope in yeast and vertebrates. Yeast two-hybrid (Y2H) assays identified physical interactions between TCU1/NUP58 and 34 proteins, including nucleoporins, SCF (Skp1/Cul1/F-box) ubiquitin ligase complex components and other nucleoplasm proteins. Genetic interactions were also found between TCU1 and genes encoding nucleoporins, soluble nuclear transport receptors and components of the ubiquitin-proteasome and auxin signaling pathways. These genetic and physical interactions indicate that TCU1/NUP58 is a member of the Nup62 subcomplex of the Arabidopsis NPC. Our findings also suggest regulatory roles for TCU1/NUP58 beyond its function in nucleocytoplasmic trafficking, a hypothesis that is supported by the Y2H and genetic interactions that we observed.
Highlights
In eukaryotes, the nuclear envelope spatially separates certain key cellular processes, segregating them to the nucleus or the cytoplasm
In addition to the nucleopore complexes (NPCs), two types of soluble nuclear transport receptors participate in nucleocytoplasmic traffic: nuclear export factors, which are involved in the exit of mRNA from the nucleus, and b-karyopherin family proteins, including importins and exportins, which transport proteins containing nuclear localization signals (NLSs) or nuclear export signals (NESs), respectively [4]
Differential interference contrast (DIC) microscopy of first- and third-node tcu1-1 and Ler leaves cleared with chloral hydrate revealed only small differences in cell number or cell size in the abaxial and adaxial epidermal layers, as well as in the subepidermal layer of palisade mesophyll cells (Figure S1)
Summary
The nuclear envelope spatially separates certain key cellular processes, segregating them to the nucleus or the cytoplasm. This segregation depends on controlled nucleocytoplasmic traffic mediated by nucleopore complexes (NPCs), which allow regulated transport of macromolecules and passive diffusion of ions and small molecules [1]. In addition to the NPC, two types of soluble nuclear transport receptors participate in nucleocytoplasmic traffic: nuclear export factors, which are involved in the exit of mRNA from the nucleus, and b-karyopherin family proteins, including importins and exportins, which transport proteins containing nuclear localization signals (NLSs) or nuclear export signals (NESs), respectively [4]. Upon direct or indirect binding of a protein to its soluble nuclear receptor, the receptor and cargo are translocated together across the central channel of the nucleopore [5]
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