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6.2 Eukaryotes
ОглавлениеThe evolution of the ancestor of a eukaryotic cell and the uptake of bacteria (endosymbiotic origin of mitochondria and chloroplasts) were a key innovation of early evolution. While the incorporation of mitochondria only occurred once in evolution, there is reasonable evidence for the assumption that the incorporation of cyanobacteria (leading to chloroplasts) occurred many times (especially within different groups of algae).
There are large differences in cellular structure and function between prokaryotes and eukaryotes. Table 1.1 summarized the important characteristics. The eukaryotic cell is distinctly further developed (Figure 1.2) and is able to carry out different processes at the same time in a single cell. This required the development of separated reaction spaces – cellular compartments (Table 1.2) – in the early stages of evolution.
A simplified overview of the origin of organisms is shown in Figures 1.1 and 6.1. Due to lack of space, it is not possible to go into more detail for the different organisms in the specific individual domains of the living kingdoms. To give biotechnologists a quick orientation about which organism they are focusing on and where these organisms stand in the tree of life, a short systematic synopsis of the organisms is put together in the following. For simplicity, only the large groups of protists (Table 6.1; Figure 6.2), plants (Table 6.2; Figure 6.3), and animals (Table 6.3; Figures 6.4 and 6.5) will be more closely characterized (a good short overview can be found in Campbell et al. (2018)). Apparently, the protozoa do not form a monophyletic clade as formerly assumed, but several independent evolutionary lineages. Traditionally, algae, and sometimes even fungi and bacteria, have been included in plants. As can be seen from Figures 6.1 and 6.2, only the metabionta with red algae, green algae, and land plants forms a monophyletic unit. Fungi cluster with Opisthokonta and thus much closer to animals and then to plants. Among animals, the Protostomia have now been separated in Ecdysozoa and Lophotrochozoa on account of molecular and anatomical data (Figure 6.4). According to the rules of cladistics, only monophyletic groups should be accepted. This requires a restructuring of some of the groups of organisms that had been grouped together, such as protists, mosses, fishes, and reptiles (Lecointre and Le Guyader 2007).
Table 6.1 Important groups of protists (model organisms or diseases caused by pathogens).
| Major protist clades | Characteristics | Example |
|---|---|---|
| Tetramastigota | Secondary loss of mitochondria | |
| Diplomonadida | Two separate cell nuclei | Giardia |
| Parabasalia | ||
| Trichomonadida | Undulating membrane | Trichomonas |
| Euglenozoa | Flagellates with or without photosynthesis | |
| Euglenophyta | Paramylon as storage polysaccharide | Euglena |
| Kinetoplastida | With kinetoplast | Trypanosoma (sleeping sickness) |
| Chromalveolata | With chloroplasts from secondary endosymbiosis | |
| Alveolata | Alveoli under the cell surface | |
| Dinoflagellata | Shell from cellulose plates | Pfiesteria |
| Apicomplexa (Sporozoa) | Apical complex for penetration of hosts | Plasmodium (malaria), Toxoplasma |
| Ciliata (ciliates) | Cilium for movement and nutrient uptake | Paramecium |
| Stramenopilata or heterokonts | With trailing and flimmer flagellum | |
| Oomyceta | Hypha; cell walls from cellulose | |
| Bacillariophyceae (diatoms) | Glassy; walls separated into two | Pinnularia |
| Chrysophyceae (golden algae) | Two flagellate cells | Dinobryon |
| Phaeophyceae (brown algae) | Brown accessory pigments | Laminaria |
| Metabionta | With chloroplasts from primary endosymbiosis | |
| Rhodobionta (red algae) | Without flagellate stage; phycoerythrin | Porphyra |
| Chlorobionta (green algae) | With chloroplasts (similar to land plants) | Chlamydomonas |
| Charophyceae | ||
| → Land plants | ||
| Unikonta | ||
| Amoebozoa | With sheet‐like form pseudopods | Amoeba |
| Mycetozoa (slime mold) | Saprophyte; amoeboid stages form colonies | Physarum, Dictyostelium |
| Opisthokonta | Protruding flagellum | |
| Fungi (Ascomycetes, Basidiomycetes) | Cell walls from chitin, saprophytic | Saccharomyces cerevisiae (yeast) |
| Amanita phalloides (deadly agaric) | ||
| Choanoflagellata | With microvilli | |
| → Metazoa (animals) |
The red, brown, and green algae were previously grouped with the plants; due to new molecular systematics, a new order has been proposed.
Important model organisms are given in bold.
Figure 6.2 Phylogenetic relationships between protists and transition to plants and animals.
Table 6.2 Systematic classification of the land plants.
| Subdivision | Class |
|---|---|
| Sporophyte (spore‐bearing plants) | |
| Moss plants | Marchantiophyta (Marchantiopsida, liverwort) |
| Anthocerotophyta (Anthoceratopsida, hornwort) | |
| Bryophyta (Bryopsida, moss) | |
| Lycophytes (club mosses) | Lycopodiophyta (Lycopodiopsida, lycopod) |
| Pteridophyta (Euphyllophytes; fern and other seedless vascular plants) | Psilotophyta (Psilotopsida, whisk fern), Sphenophyta (Equisetopsida, horsetail) |
| Filicophyta (Filicopsida, fern) | |
| Spermatophyta (seed‐bearing plants) | |
| Gymnospermae (naked seed plants) | Ginkgophyta (Ginkgopsida, Ginkgo plant) |
| Cycadophyta (Cycadopsida, palm fern) | |
| Gnetophyta (Gnetopsida, joint‐fir family) | |
| Pinophyta (Pinopsida, conifers) | |
| Angiospermae (flowering plants) | Magnoliophyta (Magnoliopsida) |
| (Arabidopsis thaliana, Nicotiana tabacum) |
Important model organisms are given in bold.
Figure 6.3 Phylogeny of land plants.
Table 6.3 Systematic classification of multicellular animals (important phyla).
| Category | Phylum | Characteristics |
|---|---|---|
| Parazoa | Porifera (sponges) | Simple multicellular animals with choanocytes that can take up bacteria by phagocytosis; cells that are mostly totipotent |
| Radiata | Cnidaria (anemones and jelly fish) (Hydra) | Stinging cells (cnidocytes) with nematocysts; developed gastrovascular system (gastric space with mouth, without anus) |
| Ctenophora (comb jellies) | Adhesive cells (colloblasts) to catch prey; eight rows of fused cilia; gastrovascular system | |
| Bilateria | ||
| Protostomia | ||
| Lophotrochozoa (150 000 species) | With lophophore and trochophore larvae | |
| Platyhelminthes (flatworms) | Dorsoventrally flattened; unsegmented; no coelom | |
| Rotifera (rotifers) | Pseudocoele with digestive tract; rotary organ; without circulatory system | |
| Ectoprocta/Bryozoa (moss animals) | With coelom; with ciliated tentacles (lophophore) for uptake of nutrients; colonial | |
| Nemertea (ribbon worms) | Coelom‐like structure for storing proboscis; closed circulatory system with blood vessels; digestive tract with mouth and anus | |
| Mollusca (mollusks) | With small coelom; three body parts: foot, visceral mass, mantle; head often reduced | |
| Annelida (segmented worms) | With small coelom and epitheliomuscular tube; segmented body and segment specialization | |
| Ecdysozoa (>1 million species) | ||
| Nematoda (roundworms) (Caenorhabditis elegans) | Cylindrical, unsegmented pseudocoelomates; complete digestive tract without circulatory system | |
| Arthropoda | With coelom and segmented body, jointed appendages; ectodermal exoskeleton | |
| Chelicerata (Arachnida) | ||
| Myriapoda | ||
| (millipedes and centipedes) | ||
| Hexapoda (insects) | ||
| (Drosophila melanogaster) | ||
| Crustaceae (crustaceans) | ||
| Deuterostomia (60 000 species) | ||
| Echinodermata (echinoderm) (starfish, sea urchin, sea cucumber) | With coelom; larvae with bilateral symmetry; adult animals with radial symmetry; ambulacral system; mesodermal endoskeleton | |
| Hemichordata | With coelom and trimeric abdominal cavity; reduced chorda; branchial gut (pharyngeal gill) | |
| Chordata (chordates) | With coelom; chorda dorsalis; dorsal tubular nerve cord branchial gut (pharyngeal gill) | |
| Urochordata | ||
| (Tunicata, tunicates) | ||
| Cephalochordata (Acrania, skull‐less) (Branchiostoma) | ||
| Vertebrata (vertebrates) | Neural crest; cephalization; spinal column; closed circulatory system | |
| Agnatha (lamprey) | ||
| Chondrichthyes (cartilaginous fish) | ||
| Osteichthyes (bony fish) | ||
| (Danio rerio) | ||
| Lissamphibia (amphibians) (Xenopus laevis) | ||
| Reptilia (reptiles) (turtle, lizard, crocodile) | ||
| Aves (birds) (Gallus gallus) | ||
| Mammalia (mammals) (Mus musculus, Homo sapiens) |
Important model organisms are given in bold.
Figure 6.4 Phylogeny of Deuterostomia and vertebrates.
Figure 6.5 Evolutionary trends in animal phylogeny.
