Mitochondria and chloroplasts as descendants of prokaryotes

A comparative plastome approach enhances the assessment of genetic variation in the Melilotus genus

BACKGROUND

Melilotus, a member of the Fabaceae family, is a pivotal forage crop that is extensively cultivated in livestock regions globally due to its notable productivity and ability to withstand abiotic stress. However, the genetic attributes of the chloroplast genome and the evolutionary connections among different Melilotus species remain unresolved.

RESULTS

In this study, we compiled the chloroplast genomes of 18 Melilotus species and performed a comprehensive comparative analysis. Through the examination of protein-coding genes, we successfully established a robust phylogenetic tree for these species. This conclusion is further supported by the phylogeny derived from single-nucleotide polymorphisms (SNPs) across the entire chloroplast genome. Notably, our findings revealed that M. infestus, M. siculus, M. sulcatus, and M. speciosus formed a distinct subgroup within the phylogenetic tree. Additionally, the chloroplast genomes of these four species exhibit two shared inversions. Moreover, inverted repeats were observed to have reemerged in six species within the IRLC. The distribution patterns of single-nucleotide polymorphisms (SNPs) and insertions/deletions (InDels) within protein-coding genes indicated that ycf1 and ycf2 accumulated nonconservative alterations during evolutionary development. Furthermore, an examination of the evolutionary rate of protein-coding genes revealed that rps18, rps7, and rpl16 underwent positive selection specifically in Melilotus.

CONCLUSIONS

We present a comparative analysis of the complete chloroplast genomes of Melilotus species. This study represents the most thorough and detailed exploration of the evolution and variability within the genus Melilotus to date. Our study provides valuable chloroplast genomic information for improving phylogenetic reconstructions and making biogeographic inferences about Melilotus and other Papilionoideae species.

Pyruvate dehydrogenase complex from baker's yeast. 2. Molecular structure, dissociation, and implications for the origin of mitochondria

1. Pyruvate dehydrogenase complex from Saccharomyces cerevisiae is similar in size (s20,w 77 S) and flavin content (1.3--1.4 nmol/mg) to the complexes from mammalian mitochondria. 2. The relative molecular masses of the constituent polypeptide chains, as determined by dodecylsulfate gel electrophoresis at different gel concentrations, were: lipoate acetyltransferase (E2), 58 000; lipoamide dehydrogenase (E3), 56 000; pyruvate dehydrogenase (E1), alpha-subunit, 45 000, and beta-subunit, 35 000. Gel chromatography in the presence of 6 M guanidine . HCl gave a value of 52 000 for E2 indicating anomalous electrophoretic migration as described for the E2 components of other pyruvate dehydrogenase complexes. Thus, the organization and subunit Mr values are similar with the mammalian complexes and virtually identical with the complexes of gram-positive bacteria but differ greatly from the pyruvate dehydrogenase complexes of gram-negative bacteria. 3. The complex was resolved into its component enzymes by the following methods. E1 was obtained by treatment of the complex with elastase followed by gel chromatography on Sepharose CL-2B using a reverse ammonium sulfate gradient for elution. E2 was isolated by gel filtration of the complex in the presence of 2 M KBr, and E3 was obtained by hydroxyapatite chromatography in 8 M urea. The isolated enzymes reassociated spontaneously to give pyruvate dehydrogenase overall activity.

Are archaebacteria merely derived 'prokaryotes'?

The archaebacteria are a group of prokaryotes which seem as distinct from the true bacteria (eubacteria) as they are from eukaryotes. The evidence on which this conclusion rests is of two types: genotypic (quantitative)--that is, comparative sequence studies, and phenotypic (qualitative)--that is, differences in various organismal characteristics. The differences between archaebacteria and true bacteria are so great, both quantitatively and qualitatively, that the two bacterial groups should be considered as representing separate primary lines of descent, each tracing directly back to the universal ancestor. Furthermore, this ancestor itself seems not to be a prokaryote; rather it was a far simpler type of organism, one properly called a progenote. If this is true, the discovery of archaebacteria marks a major advance in the biologist's attempts to understand the basis for the evolution of the cell.

Leukemic mitochondria. II. Acute monoblastic leukemia

Qualitative and quantitative ultrastructural studies were performed on mitochondria of leukemic monoblasts from 15 patients with acute monoblastic leukemia. Similar comparative observations were made on mitochondria of myeloblasts from 14 hematologically normal controls. No significant quantitative differences were noted between normal and leukemic mitochondria. Area measurements were approximately equal. Qualitative differences between the two groups consisted of increased numbers of irregularly shaped mitochondria, damaged mitochondrial membranes, mitochondria with damaged matrix, and small granules in mitochondria in the leukemic group. Leukemic cells exhibited nuclear-mitochondrial contact and virus-like particles within damaged mitochondria. To confirm the presence of virus-like particles and to aid in our understanding of nuclear-mitochondrial interaction, a C-type virus producer MSV-MLV infected rat embryo cell culture was used for additional analysis. Mitochondrial abnormalities and increased frequency of virus in damaged mitochondria, often attached to mitochondrial membranes, were noted. Several lysosomes exhibited accumulations of virus and budding into lysosomes from lysosomal membranes. Mitochondria are important organelles in glycolytic-oxidative phosphorylation pathways, and carry extranuclear genetic information. Further studies of morphologic and biochemical abnormalities of leukemic mitochondria and the interaction between the mitochondria and the nuclei in leukemic cells are needed to provide researchers with data on extranuclear factors operating in oncogenesis.

Phylogenetic origin of the chloroplast

The 16S ribosomal RNA of the chloroplast of Euglena gracilis strain Z has been characterized in terms of its 2-dimensional electrophoretic "fingerprint" (T1 ribonuclease). Over 100 spots were resolved on the "fingerprint" and each spot was characterized as to which RNA oligonucleotide fragment(s) is contained. When compared to similar analyses of prokaryotic 16S rRNAs and eukaryotic cytoplasmic 18S rRNAs, the chloroplast 16S rRNA was a typically prokaryotic RNA, but bore little if any relationship to eukaryotic 18S rRNAs. Therefore, the cistrons for chloroplast 16S rRNA are related to the equivalent prokaryotic cistrons, but, apparently, are not related to the equivalent eukaryotic cistrons. Among the organisms available for comparison, the Euglena chloroplast 16S rRNA appears most closely related to the 16S rRNA of the eukaryote, Porphyridium cruentum (a red alga), and at least distantly related to the 16S rRNAs of the blue-green algae and perhaps also to the bacilli.

Mesosomes: membranous bacterial organelles

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