Retrotransposable elements are widely distributed and diverse in eukaryotes. Their copy number increases through reverse-transcription-mediated propagation, while they can be lost through recombinational processes, generating genomic rearrangements. We previously identified extensive structurally uniform retrotransposon groups in which no member contains the gag, pol, or env internal domains. Because of the lack of protein-coding capacity, these groups are non-autonomous in replication, even if transcriptionally active. The Cassandra element belongs to the non-autonomous group called terminal-repeat retrotransposons in miniature (TRIM). It carries 5S RNA sequences with conserved RNA polymerase (pol) III promoters and terminators in its long terminal repeats (LTRs). Here, we identified multiple extended tandem arrays of Cassandra retrotransposons within different plant species, including ferns. At least 12 copies of repeated LTRs (as the tandem unit) and internal domain (as a spacer), giving a pattern that resembles the cellular 5S rRNA genes, were identified. A cytogenetic analysis revealed the specific chromosomal pattern of the Cassandra retrotransposon with prominent clustering at and around 5S rDNA loci. The secondary structure of the Cassandra retroelement RNA is predicted to form super-loops, in which the two LTRs are complementary to each other and can initiate local recombination, leading to the tandem arrays of Cassandra elements. The array structures are conserved for Cassandra retroelements of different species. We speculate that recombination events similar to those of 5S rRNA genes may explain the wide variation in Cassandra copy number. Likewise, the organization of 5S rRNA gene sequences is very variable in flowering plants; part of what is taken for 5S gene copy variation may be variation in Cassandra number. The role of the Cassandra 5S sequences remains to be established.

• Klíčová slova
• 5S RNA gene, Cassandra TRIM, ectopic recombination, genome evolution, long tandem array, retrotransposon,
• MeSH
• chromozomy hmyzu MeSH
• fylogeneze MeSH
• genom rostlinný MeSH
• genomika metody   MeSH
• interakce hostitele a parazita genetika   MeSH
• koncové repetice * MeSH
• konformace nukleové kyseliny MeSH
• molekulární evoluce MeSH
• můry genetika   MeSH
• rekombinace genetická MeSH
• retroelementy * MeSH
• RNA ribozomální 5S genetika   MeSH
• rostliny genetika   parazitologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• retroelementy * MeSH
• RNA ribozomální 5S MeSH

We have isolated and characterized a novel giant retroelement, named Ogre, which is over 22 kb long and makes up at least 5% of the pea (Pisum sativum L.) genome. This element can be classified as a Ty3/gypsy-like LTR retrotransposon based on the presence of long terminal repeats (LTRs) and the order of the domains coding for typical retrotransposon proteins. In addition to its extreme length, it has several features which make it unique among the retroelements described so far: (1) the sequences coding for gag and prot proteins are separated from the rt/rh-int domains by several stop codons; (2) the region containing these stop codons is removed from the element transcripts by splicing which results in reconstitution of the complete gag-pol coding sequence; (3) only a part of the transcripts is spliced which probably determines the ratio of translated proteins; (4) the element contains an extra ORF located upstream the gag-pol coding sequences, potentially coding for a protein of 546-562 amino acids with unknown function. The transcriptional activity of the Ogre elements has been detected in all organs tested (leaves, roots, flowers) as well as in wounded leaves and protoplasts. Considering this retroelement's constitutive expression and observed high mutual similarity of the element genomic sequences, it is possible to speculate about its recent amplification in the genomes of pea and other legume plants.

• MeSH
• alternativní sestřih * MeSH
• DNA rostlinná chemie   genetika   MeSH
• Fabaceae genetika   MeSH
• genetická transkripce * MeSH
• genom rostlinný MeSH
• hrách setý genetika   MeSH
• molekulární sekvence - údaje MeSH
• otevřené čtecí rámce genetika   MeSH
• regulace genové exprese u rostlin MeSH
• retroelementy genetika   MeSH
• sekvence nukleotidů MeSH
• sekvenční analýza DNA MeSH
• sekvenční homologie nukleových kyselin MeSH
• sekvenční seřazení MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA rostlinná MeSH
• retroelementy MeSH