Recent work revealed that, in the genomes of polyploid wheat, there exists a class of low_copy and chromosome_specific sequences that are labile upon polyploid formation. This class of sequences was proposed to play ...Recent work revealed that, in the genomes of polyploid wheat, there exists a class of low_copy and chromosome_specific sequences that are labile upon polyploid formation. This class of sequences was proposed to play a critical role in the stabilization and establishment of nascent plant polyploids as new species. To further study this issue, five wheat chromosome 7B_specific sequences, isolated from common wheat (Triticum aestivum L.) by chromosome microdissection, were characterized. The sequences were studied by genomic Southern hybridizations on a collection of polyploid wheats and their diploid progenitors. Four sequences hybridized to all polyploid species, but at the diploid level to only species closely related to the B_genome of polyploid wheat. This indicates that these sequences originated with the divergence of the diploid species, and was then vertically transmitted to polyploids. One sequence hybridized to all species at both the diploid and polyploid levels, suggesting its elimination after the polyploid wheat formation. The hybridization of this sequence to two synthetic polyploid wheats indicated that sequence elimination is a rapid event and probably related to methylation status of the sequence. Based on the above results, we suggest that selective changes of low_copy sequences occur rapidly after polyploid formation, which may contribute to the differentiation of chromosomes in newly formed allopolyploid wheats.展开更多
Processing of pre-rRNA is one of the major events taking place In the nucleolus. U3 snoRNA, an rRNA spliceosomal factor, is suggested to be essential in the first cleavage step of the 5' ETS sequence in the proces...Processing of pre-rRNA is one of the major events taking place In the nucleolus. U3 snoRNA, an rRNA spliceosomal factor, is suggested to be essential in the first cleavage step of the 5' ETS sequence in the processing of pre-rRNA. Identification of U3 in the nucleolus provides a piece of indirect evidence for pre-rRNA processing site and transportation of processing products. In the present study, subnucleolar distribution of U3 snoRNA in the nucleolus of Pisum sativum L. was studied by in situ hybridization with a U3 snoRNA probe. The results showed that the U3 labeling signals were distributed throughout dense fibrillar components (DFCs) and granular components (GCs), while no signal was found in fibrillar centers (FCs). When treated with actinomycine D (AMD), the labeling signals were decreased. Along with the increase of the AMD treatment time, the labeling signals became fewer and they were found in the distal regions of DFC and GC. Our results indicated that pre-rRNA splicing took place in the regions of DFC and GC, and the transportation of pre-rRNA processing products was from the regions around FCs towards the distal regions.展开更多
文摘Recent work revealed that, in the genomes of polyploid wheat, there exists a class of low_copy and chromosome_specific sequences that are labile upon polyploid formation. This class of sequences was proposed to play a critical role in the stabilization and establishment of nascent plant polyploids as new species. To further study this issue, five wheat chromosome 7B_specific sequences, isolated from common wheat (Triticum aestivum L.) by chromosome microdissection, were characterized. The sequences were studied by genomic Southern hybridizations on a collection of polyploid wheats and their diploid progenitors. Four sequences hybridized to all polyploid species, but at the diploid level to only species closely related to the B_genome of polyploid wheat. This indicates that these sequences originated with the divergence of the diploid species, and was then vertically transmitted to polyploids. One sequence hybridized to all species at both the diploid and polyploid levels, suggesting its elimination after the polyploid wheat formation. The hybridization of this sequence to two synthetic polyploid wheats indicated that sequence elimination is a rapid event and probably related to methylation status of the sequence. Based on the above results, we suggest that selective changes of low_copy sequences occur rapidly after polyploid formation, which may contribute to the differentiation of chromosomes in newly formed allopolyploid wheats.
文摘Processing of pre-rRNA is one of the major events taking place In the nucleolus. U3 snoRNA, an rRNA spliceosomal factor, is suggested to be essential in the first cleavage step of the 5' ETS sequence in the processing of pre-rRNA. Identification of U3 in the nucleolus provides a piece of indirect evidence for pre-rRNA processing site and transportation of processing products. In the present study, subnucleolar distribution of U3 snoRNA in the nucleolus of Pisum sativum L. was studied by in situ hybridization with a U3 snoRNA probe. The results showed that the U3 labeling signals were distributed throughout dense fibrillar components (DFCs) and granular components (GCs), while no signal was found in fibrillar centers (FCs). When treated with actinomycine D (AMD), the labeling signals were decreased. Along with the increase of the AMD treatment time, the labeling signals became fewer and they were found in the distal regions of DFC and GC. Our results indicated that pre-rRNA splicing took place in the regions of DFC and GC, and the transportation of pre-rRNA processing products was from the regions around FCs towards the distal regions.
