INTRODUCTION: Gnetophytes, comprising the genera Ephedra, Gnetum and Welwitschia, are an understudied, enigmatic lineage of gymnosperms with a controversial phylogenetic relationship to other seed plants. Here we examined the organization of ribosomal DNA (rDNA) across representative species. METHODS: We applied high-throughput sequencing approaches to isolate and reconstruct rDNA units and to determine their intragenomic homogeneity. In addition, fluorescent in situ hybridization and Southern blot hybridization techniques were used to reveal the chromosome and genomic organization of rDNA. KEY RESULTS: The 5S and 35S rRNA genes were separate (S-type) in Gnetum montanum, Gnetum gnemon and Welwitschia mirabilis and linked (L-type) in Ephedra altissima. There was considerable variability in 5S rDNA abundance, ranging from as few as ~4000 (W. mirabilis) to >100 000 (G. montanum) copies. A similar large variation was also observed in 5S rDNA locus numbers (two to 16 sites per diploid cell). 5S rRNA pseudogenes were interspersed between functional genes forming a single unit in E. altissima and G. montanum. Their copy number was comparable or even higher than that of functional 5S rRNA genes. In E. altissima internal transcribed spacers of 35S rDNA were long and intrinsically repetitive while in G. montanum and W. mirabilis they were short without the subrepeats. CONCLUSIONS: Gnetophytes are distinct from other gymnosperms and angiosperms as they display surprisingly large variability in rDNA organization and rDNA copy and locus numbers between genera, with no relationship between copy numbers and genome sizes apparent. Concerted evolution of 5S rDNA units seems to have led to the amplification of 5S pseudogenes in both G. montanum and E. altissima. Evolutionary patterns of rDNA show both gymnosperm and angiosperm features underlining the diversity of the group.
Photoprotective non-photochemical quenching (NPQ) represents an effective way to dissipate the light energy absorbed in excess by most phototrophs. It is often claimed that NPQ formation/relaxation kinetics are determined by xanthophyll composition. We, however, found that, for the alveolate alga Chromera velia, this is not the case. In the present paper, we investigated the reasons for the constitutive high rate of quenching displayed by the alga by comparing its light harvesting strategies with those of a model phototroph, the land plant Spinacia oleracea. Experimental results and in silico studies support the idea that fast quenching is due not to xanthophylls, but to intrinsic properties of the Chromera light harvesting complex (CLH) protein, related to amino acid composition and protein folding. The pKa for CLH quenching was shifted by 0.5 units to a higher pH compared with higher plant antennas (light harvesting complex II; LHCII). We conclude that, whilst higher plant LHCIIs are better suited for light harvesting, CLHs are 'natural quenchers' ready to switch into a dissipative state. We propose that organisms with antenna proteins intrinsically more sensitive to protons, such as C. velia, carry a relatively high concentration of violaxanthin to improve their light harvesting. In contrast, higher plants need less violaxanthin per chlorophyll because LHCII proteins are more efficient light harvesters and instead require co-factors such as zeaxanthin and PsbS to accelerate and enhance quenching.
- MeSH
- Alveolata fyziologie MeSH
- bílkoviny řas metabolismus MeSH
- fotosyntéza * MeSH
- protony * MeSH
- protozoální proteiny metabolismus MeSH
- rostlinné proteiny metabolismus MeSH
- Spinacia oleracea fyziologie MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
A phylogenetic tree at the species level is still far off for highly diverse insect orders, including the Coleoptera, but the taxonomic breadth of public sequence databases is growing. In addition, new types of data may contribute to increasing taxon coverage, such as metagenomic shotgun sequencing for assembly of mitogenomes from bulk specimen samples. The current study explores the application of these techniques for large-scale efforts to build the tree of Coleoptera. We used shotgun data from 17 different ecological and taxonomic datasets (5 unpublished) to assemble a total of 1942 mitogenome contigs of >3000 bp. These sequences were combined into a single dataset together with all mitochondrial data available at GenBank, in addition to nuclear markers widely used in molecular phylogenetics. The resulting matrix of nearly 16,000 species with two or more loci produced trees (RAxML) showing overall congruence with the Linnaean taxonomy at hierarchical levels from suborders to genera. We tested the role of full-length mitogenomes in stabilizing the tree from GenBank data, as mitogenomes might link terminals with non-overlapping gene representation. However, the mitogenome data were only partly useful in this respect, presumably because of the purely automated approach to assembly and gene delimitation, but improvements in future may be possible by using multiple assemblers and manual curation. In conclusion, the combination of data mining and metagenomic sequencing of bulk samples provided the largest phylogenetic tree of Coleoptera to date, which represents a summary of existing phylogenetic knowledge and a defensible tree of great utility, in particular for studies at the intra-familial level, despite some shortcomings for resolving basal nodes.
- MeSH
- algoritmy MeSH
- brouci klasifikace genetika MeSH
- databáze genetické MeSH
- fylogeneze * MeSH
- metagenomika * MeSH
- mitochondrie genetika MeSH
- sekvence nukleotidů MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
To study the relationship between uniparental rDNA (encoding 18S, 5.8S and 26S ribosomal RNA) silencing (nucleolar dominance) and rRNA gene dosage, we studied a recently emerged (within the last 80 years) allotetraploid Tragopogon mirus (2n=24), formed from the diploid progenitors T. dubius (2n=12, D-genome donor) and T. porrifolius (2n=12, P-genome donor). Here, we used molecular, cytogenetic and genomic approaches to analyse rRNA gene activity in two sibling T. mirus plants (33A and 33B) with widely different rRNA gene dosages. Plant 33B had ~400 rRNA genes at the D-genome locus, which is typical for T. mirus, accounting for ~25% of total rDNA. We observed characteristic expression dominance of T. dubius-origin genes in all organs. Its sister plant 33A harboured a homozygous macrodeletion that reduced the number of T. dubius-origin genes to about 70 copies (~4% of total rDNA). It showed biparental rDNA expression in root, flower and callus, but not in leaf where D-genome rDNA dominance was maintained. There was upregulation of minor rDNA variants in some tissues. The RNA polymerase I promoters of reactivated T. porrifolius-origin rRNA genes showed reduced DNA methylation, mainly at symmetrical CG and CHG nucleotide motifs. We hypothesise that active, decondensed rDNA units are most likely to be deleted via recombination. The silenced homeologs could be used as a 'first reserve' to ameliorate mutational damage and contribute to evolutionary success of polyploids. Deletion and reactivation cycles may lead to bidirectional homogenisation of rRNA arrays in the long term.
- MeSH
- genová dávka * MeSH
- geny rRNA * MeSH
- metylace DNA MeSH
- molekulární evoluce MeSH
- molekulární sekvence - údaje MeSH
- organizátor jadérka MeSH
- polyploidie MeSH
- promotorové oblasti (genetika) MeSH
- RNA ribozomální 18S genetika MeSH
- RNA ribozomální 5.8S genetika MeSH
- RNA ribozomální genetika MeSH
- rostlinné geny * MeSH
- sekvenční analýza DNA MeSH
- sekvenční delece MeSH
- Tragopogon genetika MeSH
- umlčování genů * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
