A considerable part of the diversity of eukaryotic phototrophs consists of algae with plastids that evolved from endosymbioses between two eukaryotes. These complex plastids are characterized by a high number of envelope membranes (more than two) and some of them contain a residual nucleus of the endosymbiotic alga called a nucleomorph. Complex plastid-bearing algae are thus chimeric cell assemblies, eukaryotic symbionts living in a eukaryotic host. In contrast, the primary plastids of the Archaeplastida (plants, green algae, red algae, and glaucophytes) possibly evolved from a single endosymbiosis with a cyanobacterium and are surrounded by two membranes. Complex plastids have been acquired several times by unrelated groups of eukaryotic heterotrophic hosts, suggesting that complex plastids are somewhat easier to obtain than primary plastids. Evidence suggests that complex plastids arose twice independently in the green lineage (euglenophytes and chlorarachniophytes) through secondary endosymbiosis, and four times in the red lineage, first through secondary endosymbiosis in cryptophytes, then by higher-order events in stramenopiles, alveolates, and haptophytes. Engulfment of primary and complex plastid-containing algae by eukaryotic hosts (secondary, tertiary, and higher-order endosymbioses) is also responsible for numerous plastid replacements in dinoflagellates. Plastid endosymbiosis is accompanied by massive gene transfer from the endosymbiont to the host nucleus and cell adaptation of both endosymbiotic partners, which is related to the trophic switch to phototrophy and loss of autonomy of the endosymbiont. Such a process is essential for the metabolic integration and division control of the endosymbiont in the host. Although photosynthesis is the main advantage of acquiring plastids, loss of photosynthesis often occurs in algae with complex plastids. This chapter summarizes the essential knowledge of the acquisition, evolution, and function of complex plastids.

• Klíčová slova
• Complex endosymbiosis, Plastid replacement, Reductive evolution,
• MeSH
• biologická evoluce * MeSH
• fylogeneze MeSH
• plastidy genetika   metabolismus   MeSH
• Rhodophyta * genetika   MeSH
• rostliny genetika   MeSH
• symbióza MeSH
• Publikační typ
• časopisecké články MeSH

Dinoflagellates are a diverse group of ecologically significant micro-eukaryotes that can serve as a model system for plastid symbiogenesis due to their susceptibility to plastid loss and replacement via serial endosymbiosis. Kareniaceae harbor fucoxanthin-pigmented plastids instead of the ancestral peridinin-pigmented ones and support them with a diverse range of nucleus-encoded plastid-targeted proteins originating from the haptophyte endosymbiont, dinoflagellate host, and/or lateral gene transfers (LGT). Here, we present predicted plastid proteomes from seven distantly related kareniaceans in three genera (Karenia, Karlodinium, and Takayama) and analyze their evolutionary patterns using automated tree building and sorting. We project a relatively limited ( ~ 10%) haptophyte signal pointing towards a shared origin in the family Chrysochromulinaceae. Our data establish significant variations in the functional distributions of these signals, emphasizing the importance of micro-evolutionary processes in shaping the chimeric proteomes. Analysis of plastid genome sequences recontextualizes these results by a striking finding the extant kareniacean plastids are in fact not all of the same origin, as two of the studied species (Karlodinium armiger, Takayama helix) possess plastids from different haptophyte orders than the rest.

• Klíčová slova
• Automated Tree Sorting, Myzozoa, Post-Endosymbiotic Organelle Evolution, Protists, Shopping Bag Model,
• MeSH
• Dinoflagellata * genetika   metabolismus   MeSH
• fylogeneze MeSH
• plastidy genetika   MeSH
• proteom genetika   metabolismus   MeSH
• symbióza genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• proteom MeSH

Eukaryotic organelles supposedly evolved from their bacterial ancestors because of their benefits to host cells. However, organelles are quite often retained, even when the beneficial metabolic pathway is lost, due to something other than the original beneficial function. The organellar function essential for cell survival is, in the end, the result of organellar evolution, particularly losses of redundant metabolic pathways present in both the host and endosymbiont, followed by a gradual distribution of metabolic functions between the organelle and host. Such biological division of metabolic labor leads to mutual dependence of the endosymbiont and host. Changing environmental conditions, such as the gradual shift of an organism from aerobic to anaerobic conditions or light to dark, can make the original benefit useless. Therefore, it can be challenging to deduce the original beneficial function, if there is any, underlying organellar acquisition. However, it is also possible that the organelle is retained because it simply resists being eliminated or digested untill it becomes indispensable.

• Klíčová slova
• benefit, endosymbiosis, essential function, mitochondrion, organelle, plastid,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Primary plastids of green algae (including land plants), red algae and glaucophytes are bounded by two membranes and are thought to be derived from a single primary endosymbiosis of a cyanobacterium in a eukaryotic host. Complex plastids of euglenids and chlorarachneans bounded by three and four membranes, respectively, most likely arose via two separate secondary endosymbioses of a green alga in a eukaryotic host. Secondary plastids of cryptophyta, haptophyta, heterokontophyta and apicomplexan parasites bounded by four membranes, and plastids of dinoflagellates bounded by three membranes could have arisen via a single secondary endosymbiosis of a red alga in a eukaryotic host (chromalveolate hypothesis). However, the scenario of separate tertiary origins (symbioses of an alga possessing secondary plastids in a eukaryotic host) of some (or even most) chromalveolate plastids can be also consistent with the current data. The protein import into complex plastids differs from the import into primary plastids, as complex plastids contain one or two extra membrane(s). In organisms with primary plastids, plastid-targeted proteins contain N-terminal transit peptide which ferries proteins through the protein import machineries (multiprotein complexes) of the two (originally cyanobacterial) membranes. In organisms with complex plastids, the secretory signal sequence directing proteins to endomembrane system and afterwards through extra outermost membrane(s) is generally present upstream of the classical transit peptide. Several free-living as well as parasitic eukaryotes possess non-photosynthetic plastids. These plastids have generally retained the plastid genome, functional plastid transcriptional and translational apparatus, and various metabolic pathways, suggesting that though these plastids lost their photosynthetic ability, they are essential for the mentioned organisms. Nevertheless, some eukaryotes could have lost chloroplast compartment completely.

• MeSH
• biologická evoluce * MeSH
• chloroplasty genetika   metabolismus   MeSH
• Eukaryota genetika   metabolismus   MeSH
• fotosyntéza * MeSH
• plastidy genetika   metabolismus   MeSH
• proteiny genetika   metabolismus   MeSH
• transport proteinů MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• proteiny MeSH