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

We analysed the size, relative age and chromosomal localization of nuclear sequences of plastid and mitochondrial origin (NUPTs-nuclear plastid DNA and NUMTs-nuclear mitochondrial DNA) in six completely sequenced plant species. We found that the largest insertions showed lower divergence from organelle DNA than shorter insertions in all species, indicating their recent origin. The largest NUPT and NUMT insertions were localized in the vicinity of the centromeres in the small genomes of Arabidopsis and rice. They were also present in other chromosomal regions in the large genomes of soybean and maize. Localization of NUPTs and NUMTs correlated positively with distribution of transposable elements (TEs) in Arabidopsis and sorghum, negatively in grapevine and soybean, and did not correlate in rice or maize. We propose a model where new plastid and mitochondrial DNA sequences are inserted close to centromeres and are later fragmented by TE insertions and reshuffled away from the centromere or removed by ectopic recombination. The mode and tempo of TE dynamism determines the turnover of NUPTs and NUMTs resulting in their species-specific chromosomal distributions.

• MeSH
• buněčné jádro MeSH
• chromozomy rostlin genetika   MeSH
• druhová specificita MeSH
• genom rostlinný MeSH
• mitochondriální DNA genetika   MeSH
• mitochondrie genetika   MeSH
• mutace INDEL genetika   MeSH
• plastidy genetika   MeSH
• rostliny genetika   MeSH
• sekvenční analýza DNA MeSH
• transpozibilní elementy DNA genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• mitochondriální DNA MeSH
• transpozibilní elementy DNA MeSH

BACKGROUND: The endosymbiotic birth of organelles is accompanied by massive transfer of endosymbiont genes to the eukaryotic host nucleus. In the centric diatom Thalassiosira pseudonana the Psb28 protein is encoded in the plastid genome while a second version is nuclear-encoded and possesses a bipartite N-terminal presequence necessary to target the protein into the diatom complex plastid. Thus it can represent a gene captured during endosymbiotic gene transfer. METHODOLOGY/PRINCIPAL FINDINGS: To specify the origin of nuclear- and plastid-encoded Psb28 in T. pseudonana we have performed extensive phylogenetic analyses of both mentioned genes. We have also experimentally tested the intracellular location of the nuclear-encoded Psb28 protein (nuPsb28) through transformation of the diatom Phaeodactylum tricornutum with the gene in question fused to EYFP. CONCLUSIONS/SIGNIFICANCE: We show here that both versions of the psb28 gene in T. pseudonana are transcribed. We also provide experimental evidence for successful targeting of the nuPsb28 fused with EYFP to the diatom complex plastid. Extensive phylogenetic analyses demonstrate that nucleotide composition of the analyzed genes deeply influences the tree topology and that appropriate methods designed to deal with a compositional bias of the sequences and the long branch attraction artefact (LBA) need to be used to overcome this obstacle. We propose that nuclear psb28 in T. pseudonana is a duplicate of a plastid localized version, and that it has been transferred from its endosymbiont.

• MeSH
• buněčné jádro genetika   MeSH
• molekulární sekvence - údaje MeSH
• plastidy genetika   MeSH
• proteiny chemie   genetika   MeSH
• rozsivky genetika   MeSH
• sekvence aminokyselin MeSH
• sekvenční homologie aminokyselin MeSH
• symbióza genetika   MeSH
• technika přenosu genů MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• proteiny 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