SIRE1, an endogenous retrovirus family from Glycine max, is highly homogeneous and evolutionarily young.

SIRE1 is unusual among Ty1-copia retrotransposons in that it has an additional open reading frame with structural features similar to retroviral envelope proteins between pol and the 3' LTR. Here we report the characterization and comparison of eight different SIRE1 elements derived from a soybean genomic library, as well as SIRE1 reverse transcriptases from Glycine soja. The DNA sequences of the eight SIRE1 elements are highly homogeneous and share greater than 95% nucleotide identity. Partial sequences obtained from BAC ends are similarly conserved. Phylogenetic analyses resolve two closely related SIRE1 lineages, and nucleotide changes within and between SIRE1 lineages have occurred to preserve function. Both the gag and the env-like genes are evolving under similar levels of functional constraint. Considerable sequence heterogeneity in the form of short duplications was found within the LTRs and in the region between the envelope-like ORF and the 3' LTR. These duplications are suggestive of slippage by reverse transcriptase during replication. Sequence identity between LTRs of individual insertions suggests that they transposed within the past 70,000 years. Two of 10 SIRE1 insertions examined abut Ty3-gypsy retroelements. Since the soybean genome harbors more than 1,000 SIRE1 insertions, the collective data suggest that SIRE1 has undergone a very recent and robust amplification in soybean.

Laten HM ，Havecker ER ，Farmer LM ，Voytas DF ... -  《MOLECULAR BIOLOGY AND EVOLUTION》

Genome-wide characterization of long terminal repeat -retrotransposons in apple reveals the differences in heterogeneity and copy number between Ty1-copia and Ty3-gypsy retrotransposons.

The conserved domains of reverse transcriptase (RT) genes of Ty1-copia and Ty3-gypsy groups of long terminal repeat (LTR) retrotransposons were isolated from the Malus domestica genome using degenerate oligonucleotide primers. Sequence analysis showed that 45% of Ty1-copia and 63% of Ty3-gypsy RT sequences contained premature stop codons and/or indels disrupting the reading frame. High heterogeneity among RT sequences of both Ty1-copia and Ty3-gypsy group retrotransposons was observed, but Ty3-gypsy group retrotransposons in the apple genome are less heterogeneous than Ty1-copia elements. Retrotransposon copy number was estimated by dot blot hybridizations for Ty1-copia (approximately 5,000) and Ty3-gypsy (approximately 26,000). All elements of the two types of LTR retrotransposons comprise approximately 38% of the M. domestica genome, with the Ty3-gypsy group contribution being higher (33.5%) than the Ty1-copia one (4.6%). Transcription was not detected by reverse transcription-polymerase chain reaction for either Ty1-copia or Ty3-gypsy retrotransposons in the leaves of plants in vitro or in leaf explants cultured on medium supplemented with high concentration benzylaminopurine. This research reveals the differences in heterogeneity and copy number between Ty1-copia and Ty3-gypsy retrotransposons in the apple genome. Ty1-copia retrotransposon has higher heterogeneity than Ty3-gypsy retrotransposon, but the latter has a higher copy number, which implies that Ty3-gypsy retrotransposons may play a more important role in the apple genome evolution.

Sun HY ，Dai HY ，Zhao GL ，Ma Y ，Ou CQ ，Li H ，Li LG ，Zhang ZH ... -  《-》

Evolutionary conservation, diversity and specificity of LTR-retrotransposons in flowering plants: insights from genome-wide analysis and multi-specific comparison.

The availability of complete or nearly complete genome sequences from several plant species permits detailed discovery and cross-species comparison of transposable elements (TEs) at the whole genome level. We initially investigated 510 long terminal repeat-retrotransposon (LTR-RT) families comprising 32370 elements in soybean (Glycine max (L.) Merr.). Approximately 87% of these elements were located in recombination-suppressed pericentromeric regions, where the ratio (1.26) of solo LTRs to intact elements (S/I) is significantly lower than that of chromosome arms (1.62). Further analysis revealed a significant positive correlation between S/I and LTR sizes, indicating that larger LTRs facilitate solo LTR formation. Phylogenetic analysis revealed seven Copia and five Gypsy evolutionary lineages that were present before the divergence of eudicot and monocot species, but the scales and timeframes within which they proliferated vary dramatically across families, lineages and species, and notably, a Copia lineage has been lost in soybean. Analysis of the physical association of LTR-RTs with centromere satellite repeats identified two putative centromere retrotransposon (CR) families of soybean, which were grouped into the CR (e.g. CRR and CRM) lineage found in grasses, indicating that the 'functional specification' of CR pre-dates the bifurcation of eudicots and monocots. However, a number of families of the CR lineage are not concentrated in centromeres, suggesting that their CR roles may now be defunct. Our data also suggest that the envelope-like genes in the putative Copia retrovirus-like family are probably derived from the Gypsy retrovirus-like lineage, and thus we propose the hypothesis of a single ancient origin of envelope-like genes in flowering plants.

Du J ，Tian Z ，Hans CS ，Laten HM ，Cannon SB ，Jackson SA ，Shoemaker RC ，Ma J ... -  《-》

Phylogenetic evidence for Ty1-copia-like endogenous retroviruses in plant genomes.

Laten HM 《GENETICA》

Analysis of insertional sites of the SIRE1 retroelement family from Glycine max using GenBank BAC-end sequences.

Flasch DA ，Rebman EK ，Olfson EH ，Nguyen KK ，Geirut LE ，Garland MC ，Lindorfer CM ，Laten HM ... -  《-》