Thioredoxins （TRX） are key components of cellular redox balance, regulating many target proteins through thiol/disulfide exchange reactions. In higher plants, TRX constitute a complex multigenic family whose members...Thioredoxins （TRX） are key components of cellular redox balance, regulating many target proteins through thiol/disulfide exchange reactions. In higher plants, TRX constitute a complex multigenic family whose members have been found in almost all cellular compartments. Although chloroplastic and cytosolic TRX systems have been largely studied, the presence of a nuclear TRX system has been elusive for a long time. Nucleoredoxins （NRX） are potential nuclear TRX found in most eukaryotic organisms. In contrast to mammals, which harbor a unique NRX, angiosperms gen- erally possess multiple NRX organized in three subfamilies. Here, we show thatArabidopsis thaliana has two NRXgenes （AtNRX1 and AtNRX2）, respectively, belonging to subgroups I and III. While NRX1 harbors typical TRX active sites （WCG/ PPC）, NRX2 has atypical active sites （WCRPC and WCPPF）. Nevertheless, both NRXl and NRX2 have disulfide reduction capacities, although NRX1 alone can be reduced by the thioredoxin reductase NTRA. We also show that both NRX1 and NRX2 have a dual nuclear/cytosolic localization. Interestingly, we found that NTRA, previously identified as a cytosolic protein, is also partially localized in the nucleus, suggesting that a complete TRX system is functional in the nucleus. We show that NRX1 is mainly found as a dimer in vivo. nrxl and nrx2 knockout mutant plants exhibit no phenotypic perturbations under standard growth conditions. However, the nrxl mutant shows a reduced pollen fertility phenotype, suggesting a specific role of NRX1 at the haploid phase.展开更多
Recent progress in understanding higher-order chromatin organization in the nucleus has been considerable. From single gene to chromosome territory, realistic biophysical models can now accurately predict some of the ...Recent progress in understanding higher-order chromatin organization in the nucleus has been considerable. From single gene to chromosome territory, realistic biophysical models can now accurately predict some of the structural feature of cell nuclei. Despite growing evidence of a deterministic nuclear organization, the physiological consequence of spatial genome organization is still unclear. In the simple eukaryotic model, Saccharomyces cerevisiae, clear correlation between gene position and transcription has been established. In this review, we will focus on higher-order chromatin organization in yeast with respect to the nuclear envelope and nucleolus. In Arabidopsis thaliana, a model plant for which we have a complete genome sequence, chromosome territory （CT） arrangement and somatic homologous pairing in interphase nuclei seem to occur randomly. Since chromosomes containing nucleolar organizer regions associate more frequently to form a single nucleolar structure, as in yeast, the nucleolus seems to play a major role in organizing nuclear space. Recent findings have begun to elucidate how plant regulatory factors, such as chromatin remodeling or histone chaperones, affect the chromatin state of ribosomal DNA genes located in two distinct CTarrangements in the nucleus. The functional outcome of yeast nuclear organization allowed us to propose how nuclear organization might contribute to a novel type of epigenetic regulation： the spatial regulation of transcription.展开更多
文摘Thioredoxins （TRX） are key components of cellular redox balance, regulating many target proteins through thiol/disulfide exchange reactions. In higher plants, TRX constitute a complex multigenic family whose members have been found in almost all cellular compartments. Although chloroplastic and cytosolic TRX systems have been largely studied, the presence of a nuclear TRX system has been elusive for a long time. Nucleoredoxins （NRX） are potential nuclear TRX found in most eukaryotic organisms. In contrast to mammals, which harbor a unique NRX, angiosperms gen- erally possess multiple NRX organized in three subfamilies. Here, we show thatArabidopsis thaliana has two NRXgenes （AtNRX1 and AtNRX2）, respectively, belonging to subgroups I and III. While NRX1 harbors typical TRX active sites （WCG/ PPC）, NRX2 has atypical active sites （WCRPC and WCPPF）. Nevertheless, both NRXl and NRX2 have disulfide reduction capacities, although NRX1 alone can be reduced by the thioredoxin reductase NTRA. We also show that both NRX1 and NRX2 have a dual nuclear/cytosolic localization. Interestingly, we found that NTRA, previously identified as a cytosolic protein, is also partially localized in the nucleus, suggesting that a complete TRX system is functional in the nucleus. We show that NRX1 is mainly found as a dimer in vivo. nrxl and nrx2 knockout mutant plants exhibit no phenotypic perturbations under standard growth conditions. However, the nrxl mutant shows a reduced pollen fertility phenotype, suggesting a specific role of NRX1 at the haploid phase.
文摘Recent progress in understanding higher-order chromatin organization in the nucleus has been considerable. From single gene to chromosome territory, realistic biophysical models can now accurately predict some of the structural feature of cell nuclei. Despite growing evidence of a deterministic nuclear organization, the physiological consequence of spatial genome organization is still unclear. In the simple eukaryotic model, Saccharomyces cerevisiae, clear correlation between gene position and transcription has been established. In this review, we will focus on higher-order chromatin organization in yeast with respect to the nuclear envelope and nucleolus. In Arabidopsis thaliana, a model plant for which we have a complete genome sequence, chromosome territory （CT） arrangement and somatic homologous pairing in interphase nuclei seem to occur randomly. Since chromosomes containing nucleolar organizer regions associate more frequently to form a single nucleolar structure, as in yeast, the nucleolus seems to play a major role in organizing nuclear space. Recent findings have begun to elucidate how plant regulatory factors, such as chromatin remodeling or histone chaperones, affect the chromatin state of ribosomal DNA genes located in two distinct CTarrangements in the nucleus. The functional outcome of yeast nuclear organization allowed us to propose how nuclear organization might contribute to a novel type of epigenetic regulation： the spatial regulation of transcription.
