共查询到20条相似文献,搜索用时 15 毫秒
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We have determined the nucleotide sequence for the Rubisco large subunit from four holoparasitic species of Orobanche. Intact open reading frames are present in two species (O. corymbosa and O. fasciculata), whereas the remaining species (O. cernua and O. ramosa) have rbcL pseudogenes. Sequences for rbcL 5'-UTRs from species of Orobanche have few changes in the promoter and ribosome binding sites compared to photosynthetic higher plants. Comparison of rbcL 3'-UTR sequences for Nicotiana, Ipomoea, Cuscuta, and Orobanche reveal that nucleotide sequences from parasitic plants have regions capable of forming stem-loop structures, but 56-69 nt are deleted upstream of the stem-loop in the parasitic plants compared to their photosynthetic relatives. Although rbcL pseudogenes of O. cernua and O. ramosa have many large and small deletions, few indels are shared in common, implying that their common ancestor probably had an intact rbcL reading frame. Intact rbcL reading frames in O. corymbosa and O. fasciculata retain a bias of synonymous over nonsynonymous substitutions and deduced protein sequences are consistent with potentially functional Rubisco large subunit proteins. A conservative model of random substitution processes in pseudogene sequences estimates that the probability is low (P < 0.028) that these sequences would retain an open reading frame by chance. Species of Orobanche have either had recent photosynthetic ancestors, implying multiple independent losses of photosynthesis in this genus, or the rbcL gene may serve an unknown function in some nonphotosynthetic plants. 相似文献
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The photosynthetic gene rbcL has been lost or dramatically altered in some lineages of nonphotosynthetic parasitic plants, but the dynamics of these events following loss of photosynthesis and whether rbcL has sustained functionally significant changes in photosynthetic parasitic plants are unknown. To assess the changes to rbcL associated with the loss of functional constraints for photosynthesis, nucleotide sequences from nonparasitic and parasitic plants of Scrophulariales were used for phylogeny reconstruction and character analysis. Plants in this group display a broad range of parasitic abilities, from photosynthetic ("hemiparasites") to nonphotosynthetic ("holoparasites"). With the exception of Conopholis (Orobanchaceae), the rbcL locus is present in all parasitic plants of Scrophulariales examined. Several holoparasitic genera included in this study, including Boschniakia, Epifagus, Orobanche, and Hyobanche, have rbcL pseudogenes. However, the holoparasites Alectra orobanchoides, Harveya capensis, Harveya purpurea, Lathraea clandestina, Orobanche corymbosa, O. fasciculata, and Striga gesnerioides have intact open reading frames (ORFs) for the rbcL gene. Phylogenetic hypotheses based on rbcL are largely in agreement with those based on sequences of the nonphotosynthetic genes rps2 and matK and show a single origin of parasitism, and loss of photosynthesis and pseudogene formation have been independently derived several times in Scrophulariales. The mutations in rbcL in nonparasitic and hemiparasitic plants would result in largely conservative amino acid substitutions, supporting the hypothesis that functional proteins can experience only a limited range of changes, even in minimally photosynthetic plants. In contrast, ORFs in some holoparasites had many previously unobserved missense substitutions at functionally important amino acid residues, suggesting that rbcL genes in these plants have evolved under relaxed or altered functional constraints. 相似文献
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Group I introns were reported for the first time in the large subunit of Rubisco (rbcL) genes, using two colonial green algae, Pleodorina californica and Gonium multicoccum (Volvocales). The rbcL gene of P. californica contained an intron (PIC intron) of 1320 bp harboring an open reading frame (ORF). The G. multicoccum rbcL gene had two ORF-lacking introns of 549 (GM1 intron) and 295 (GM2 intron) base pairs. Based on the conserved nucleotide sequences of the secondary structure, the PIC and GM1 introns were assigned to group IA2 whereas the GM2 intron belonged to group IA1. Southern hybridization analyses of nuclear and chloroplast DNAs indicated that such intron-containing rbcL genes are located in the chloroplast genome. Sequencing RNAs from the two algae revealed that these introns are spliced out during mRNA maturation. In addition, the PIC and GM1 introns were inserted in the same position of the rbcL exons, and phylogenetic analysis of group IA introns indicated a close phylogenetic relationship between the PIC and GM1 introns within the lineage of bacteriophage group IA2 introns. However, P. californica and G. multicoccum occupy distinct clades in the phylogenetic trees of the colonial Volvocales, and the majority of other colonial volvocalean species do not have such introns in the rbcL genes. Therefore, these introns might have been recently inserted in the rbcL genes independently by horizontal transmission by viruses or bacteriophage. 相似文献
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The rbcL gene sequence from chestnut indicates a slow rate of evolution in the Fagaceae 总被引:2,自引:0,他引:2
The nucleotide sequence was obtained for the chloroplast gene coding for the large subunit of the ribulose 1,5-bisphosphate carboxylase (rbcL) of chestnut (Castanea sativa Mill.), a member of the woody family Fagaceae. Amplification primers downstream and upstream the rbcL open reading frame are also described. By comparing with other angiosperm sequences, we show that the rate of evolution of rbcL in the family Fagaceae is much slower than that observed for the families of annuals analyzed. 相似文献
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EE Mason 《Canadian Metallurgical Quarterly》1998,8(5):524-529
The ribulose bisphosphate carboxylase/oxygenase rbcL and rbcS genes of a carbon monoxide-oxidizing bacterium, Hydrogenophaga pseudoflava DSM 1084, were cloned and sequenced. The cloned rbcL and rbcS genes had open reading frames of 1422 and 351 nucleotides encoding RbcL and RbcS with calculated molecular masses of 52,689 and 13,541, respectively. The known active site residues in other RbcL proteins were conserved in the H. pseudoflava proteins. The H. pseudoflava RbcS protein lacked the 12-residue internal sequence found in the plant enzymes. The 2 genes were separated by a 134 bp intergenic region and cotranscribed as a 2.0 kb rbcLS mRNA. Novel two perfect 9 bp direct repeats overlapping with two dyad symmetries were found in the rbcLS promoter region. 相似文献
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The nucleotide sequences of the ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit gene (rbcL) of Glycyrrhiza glabra, G. uralensis, G. inflata, G. echinata, and G. pallidiflora have been determined to construct the phylogenetic tree. In the phylogenetic tree based on the rbcL sequences, the five Glycyrrhiza species were divided into two groups: the three glycyrrhizin-producing species G. glabra, G. uralensis, and G. inflata; and the two glycyrrhizin-nonproducing species G. echinata and G. pallidiflora. Among the three glycyrrhizin-producing species, only two nucleotide substitutions were observed between the rbcL sequence of G. glabra and G. uralensis, and the sequence of G. uralensis was identical to that of G. inflata, indicating that the three glycyrrhizin-producing species are closely related. 相似文献
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The region between the rbcL and atpB chloroplast genes and the first 53 codons of the rbcL gene have been sequenced for 19 species of angiosperms. Nine of these belong to the four largest families within the order Celastrales sensu Cronquist (i.e., Aquifoliaceae s.l., Icacinaceae, Celastraceae, and Hippocrateaceae). Both phenetic and cladistic approaches were used to test the monophyly of the order and to specify its relationships with Euphorbiaceae, Rhamnaceae, Rosaceae, and Theaceaea. Based upon this molecular analysis, the order Celastrales is polyphyletic and is divided into two major clades. The first group, containing Aquifoliaceae s.l. and Icacina, is related to Camellia (Theaceae). The second, containing Euonymus (Celastraceae), Hippocratea, and Salacia (Hippocrateaceae), is related to Euphorbia (Euphorbiaceae). 相似文献
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L Savard P Li SH Strauss MW Chase M Michaud J Bousquet 《Canadian Metallurgical Quarterly》1994,91(11):5163-5167
We have estimated the time for the last common ancestor of extant seed plants by using molecular clocks constructed from the sequences of the chloroplastic gene coding for the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) and the nuclear gene coding for the small subunit of rRNA (Rrn18). Phylogenetic analyses of nucleotide sequences indicated that the earliest divergence of extant seed plants is likely represented by a split between conifer-cycad and angiosperm lineages. Relative-rate tests were used to assess homogeneity of substitution rates among lineages, and annual angiosperms were found to evolve at a faster rate than other taxa for rbcL and, thus, these sequences were excluded from construction of molecular clocks. Five distinct molecular clocks were calibrated using substitution rates for the two genes and four divergence times based on fossil and published molecular clock estimates. The five estimated times for the last common ancestor of extant seed plants were in agreement with one another, with an average of 285 million years and a range of 275-290 million years. This implies a substantially more recent ancestor of all extant seed plants than suggested by some theories of plant evolution. 相似文献
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S Rodermel J Haley CZ Jiang CH Tsai L Bogorad 《Canadian Metallurgical Quarterly》1996,93(9):3881-3885
Multimeric protein complexes in chloroplasts and mitochondria are generally composed of products of both nuclear and organelle genes of the cell. A central problem of eukaryotic cell biology is to identify and understand the molecular mechanisms for integrating the production and accumulation of the products of the two separate genomes. Ribulose bisphosphate carboxylase (Rubisco) is localized in the chloroplasts of photosynthetic eukaryotic cells and is composed of small subunits (SS) and large subunits (LS) coded for by nuclear rbcS and chloroplast rbcL genes, respectively. Transgenic tobacco plants containing antisense rbcS DNA have reduced levels of rbcS mRNA, normal levels of rbcL mRNA, and coordinately reduced LS and SS proteins. Our previous experiments indicated that the rate of translation of rbcL mRNA might be reduced in some antisense plants; direct evidence is presented here. After a short-term pulse there is less labeled LS protein in the transgenic plants than in wild-type plants, indicating that LS accumulation is controlled in the mutants at the translational and/or posttranslational levels. Consistent with a primary restriction at translation, fewer rbcL mRNAs are associated with polysomes of normal size and more are free or are associated with only a few ribosomes in the antisense plants. Effects of the rbcS antisense mutation on mRNA and protein accumulation, as well as on the distribution of mRNAs on polysomes, appear to be minimal for other chloroplast and nuclear photosynthetic genes. Our results suggest that SS protein abundance specifically contributes to the regulation of LS protein accumulation at the level of rbcL translation initiation. 相似文献