Reconstructing the history of plastid acquisition and loss in the alveolate protists is a difficult problem because our knowledge of the distribution of plastids in extant lineages is incomplete due to the possible presence of cryptic, nonphotosynthetic plastids in several lineages. The discovery of the apicoplast in apicomplexan parasites has drawn attention to this problem and, more specifically, to the question of whether many other nonphotosynthetic lineages also contain cryptic plastids or…

The mitochondrial genome and the expression of the genes within it have evolved to be highly unusual in several lineages. Within alveolates, apicomplexans and dinoflagellates share the most reduced mitochondrial gene content on record, but differ from one another in organisation and function. To clarify how these characteristics originated, we examined mitochondrial genome form and expression in a key lineage that arose close to the divergence of apicomplexans and dinoflagellates, Oxyrrhis…

Sequence variability of RPCS (repetitive PuvII Ctenomys sequence), the major satellite DNA of octodontid Ctenomys rodents, was analysed in species belonging to three groups of species representing the two patterns of karyotypic evolution in the genus: stable and dynamic karyotypes among closely related species. The studied species represent the overall range of RPCS copy number (2000–6.6×10(6) copies per haploid genome) in the genus. RPCS sequence was characterised by PCR amplification of the…

Molecular phylogenies of euglenids are usually based on ribosomal RNA genes that do not resolve the branching order among the deeper lineages. We addressed deep euglenid phylogeny using the cytosolic form of the heat-shock protein 90 gene (hsp90), which has already been employed with some success in other groups of euglenozoans and eukaryotes in general. Hsp90 sequences were generated from three taxa of euglenids representing different degrees of ultrastructural complexity, namely Petalomonas…

The introduction of plastids into different heterotrophic protists created lineages of algae that diversified explosively, proliferated in marine and freshwater environments, and radically altered the biosphere. The origins of these secondary plastids are usually inferred from the presence of additional plastid membranes. However, two examples provide unique snapshots of secondary-endosymbiosis-in-action, because they retain a vestige of the endosymbiont nucleus known as the nucleomorph. These…

The number of cases of lateral or horizontal gene transfer in eukaryotic genomes is growing steadily, but in most cases, neither the donor nor the recipient is known, and the biological implications of the transfer are not clear. We describe a relatively well-defined case of transfer from a cyanobacterial source to an ancestor of dinoflagellates that diverged before Oxyrrhis but after Perkinsus. This case is also exceptional in that 2 adjacent genes, a paralogue of the shikimate biosynthetic…

The general secretory (Sec) pathway is the main mechanism for protein secretion and insertion into endoplasmic reticulum and plasma membrane in prokaryotes and eukaryotes. However, the complete genome of the highly specialized microsporidian parasite Encephalitozoon cuniculi appears to lack a gene for Sec61beta, one of three universally conserved proteins that form the core of the Sec translocon. We have identified a putative, highly divergent homologue of Sec61beta in the genome of another…

CONCLUSION: The Streblomastix data show that the genome of the ancestor of excavates likely contained many introns and the subsequent evolution of introns has proceeded very differently in different excavate lineages: in Streblomastix there has been much stasis while in Trichomonas and Giardia most introns have been lost.

In pyrophosphate-dependent glycolysis, the ATP/ADP-dependent enzymes phosphofructokinase (PFK) and pyruvate kinase are replaced by the pyrophosphate-dependent PFK and pyruvate phosphate dikinase (PPDK), respectively. This variant of glycolysis is widespread among bacteria, but it also occurs in a few parasitic anaerobic eukaryotes such as Giardia and Entamoeba spp. We sequenced two genes for PPDK from the amitochondriate oxymonad Streblomastix strix and found evidence for PPDK in Trichomonas…

Eukaryotic nuclear genomes are generally considered to be large and gene-sparse, but extreme reduction has taken place several times, resulting in small genomes with a high gene-density. This process involves losing genes, compacting those that remain, or often both. Recently sequenced nuclear genomes include several that have converged to similar gene-densities by many means: variation in numbers and lengths of genes, intergenic regions and introns all contribute, but not equally in any given…