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4 Cascades of Convergent Evolution: The Corresponding Evolutionary Histories of Euglenozoans and Dinoflagellates--Julius Lukeš, Brian S. Leander, and Patrick J. Keeling
Pages 65-84

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From page 65...
... Moreover, the appearance of one deviation in an ances tor can constrain the set of possible downstream deviations in its descendents, so features that might be independent function ally can still be evolutionarily linked. What functional advantage Biology Centre, institute of Parasitology, Czech Academy of sciences, and Faculty of sci ˇ ences, University of south Bohemia, 37005 Ceské Budejovice, Czech republic; and †Canadian ˇ institute for Advanced research, Program in integrated Microbial Biodiversity, Departments of Botany and Zoology, University of British Columbia, vancouver, Canada v6T 1Z4.
From page 66...
... T he vast majority of eukaryotes on the planet, in terms of both abundance and diversity, are microbial. Generalities about funda mental biological processes are based on knowledge of a few model organisms, yet many microeukaryotes have deviated well beyond these generalities over the course of evolutionary history, which is a reflection of the deep phylogenetic distances between eukaryotic lineages that are neither plants nor animals nor fungi.
From page 67...
... , whereas the euglenozoa consists of euglenids, kinetoplastids, and diplonemids (illustrated in Upper Right; scanning electron micrographs of Lepocinclis, Leptomonas, and Diplonema)
From page 68...
... Below, we will examine some of these examples of convergence and what the cooccurrence of convergent traits may tell us about how they evolved. CONVERGENT EVOLUTION recognizing the independent origins of similar traits in distantly related lineages -- convergent evolution -- allows us to better understand how different environmental and intrinsic conditions have shaped the characteristics of organisms over time; each specific example of convergence reflects a fundamental biological problem and its possible solutions.
From page 69...
... eukaryotic cells are built from a few core systems that have become tremendously diverse over the course of evolutionary history. some systems are remarkably conserved, in particular fundamental molecular processes such as information flow or core metabolism, but even in these systems substantial modifications accumulated in some lineages.
From page 70...
... (C) TeM through the cell surface or pellicle of a euglenid cell showing the proteinaceous strips (asterisk)
From page 71...
... Many free-living euglenids and dinoflagellates engulf prey organisms using sophisticated feeding apparatuses positioned on the ventral side of the cell. Although the evolution of these apparatuses is a shared fea cell surface of a euglenid cell (Peranema)
From page 72...
... By contrast, the diversity and complexity of feeding apparatuses in dinoflagellates probably reflect independent origins in different lineages within the group. The feeding apparatus in dinoflagellates can be simple pockets that unzip when prey is drawn into the cell, dynamic siphons that suck out the cytoplasm of prey cells in a straw-like fashion or expansive veils that completely envelop large filamentous prey and fold it methodically into manageable packets small enough to ingest.
From page 73...
... As described in the next 3 sections, the molecular processes associated with the nucleus, plastid, and mitochondrion also reflect high levels of convergent evolution. THE NUCLEUS: SPLICED LEADERS AND POLYCISTRONIC mRNA PROCESSING The nuclear genomes of kinetoplastids and dinoflagellates have both acquired a long list of unusual characteristics.
From page 74...
... . The second major oddity shared by kinetoplastid and dinoflagellate nuclear gene expression is the presence of polycistronic messages.
From page 75...
... . These gene repeats are cotranscribed, resulting in polycistronic messages, and different from those of kinetoplastids because mrnAs have so far only been found to carry multiple copies of a single gene (Bachvaroff and Place, 2008)
From page 76...
... For example, the establishment of widespread sl addition in a nuclear genome could precondition that genome for the subsequent establishment of polycistronic transcription. Polycistronic mrnAs that would otherwise be deleterious could flourish simply because the processing pathway eliminates their deleterious effect (the inability to translate all but the first cistron)
From page 77...
... euglenophyte plastid genomes are home to some unique self-splicing introns (Copertino and hallick, 1993) , whereas the dinoflagellate plastid genome has been massively reduced in coding content and broken into single gene minicircles with polyuridylylated transcripts (Wang and Morse, 2006)
From page 78...
... THE MITOCHONDRION: RNA EDITING AND GENOME BREAKDOWN The mitochondrial genomes of dinoflagellates and kinetoplastids are both highly unorthodox, and once again have evolved some unique features and several common complex characteristics. The kinetoplastid mitochondrion contains uniquely structured, protein-rich mitochondrial ribosomes with a reduced rnA component, unusual fatty acid synthesis and respiratory complexes such as the prokaryotic-like complex i, alternative terminal oxidase, massive trnA import, and incomplete Krebs cycle.
From page 79...
... in dinoflagellates, the ge small grnAs nome is also fragmented but into multiple potentially linear pieces encoding 1 or x 37, editableore genes or gene fragments. only 3 genes are encoded in the genome (cox1, m cox3, and cob)
From page 80...
... . These lineages have the smallest mitochondrial genomes known, with most species examined with just 3 protein-coding genes: cox1, cox3, and cob (strictly speaking, the dinoflagellate Oxyrrhis has only 2 genes since cob and cox3 are expressed as a fusion)
From page 81...
... The genes, such as they are, are encoded on the maxicircles and expressed as polycistronic mrnAs, but after processing into monocistrons these messages are then massively altered by the insertion and deletion of uridine residues (up to 553 insertions and 89 deletions in a single mrnA)
From page 82...
... even if these characteristics are not obligatorily functionally linked, their evolution may be tightly linked. For example, polycistronic mrnAs can exist without an sl, but they are evolutionarily linked because adding the sl allows the polycistronic mrnA to function.
From page 83...
... . Within this framework, together with the recognition that the evolution of an unusual character can be an intrinsic factor in the subsequent evolution of additional, specific characters, a complex cellular system may be explained simply by identifying the event(s)
From page 84...
... 4.1 and 4.2F, respectively. This work was supported by the Grant Agency of the Czech republic Grant 204/09/1667 (to J.l.)


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