Nested Ty3-gypsy retrotransposons of a single Beta procumbens centromere contain a putative chromodomain

Abstract

LTR retrotransposons belong to a major group of DNA sequences that are often localized in plant centromeres. Using BAC inserts originating from the centromere of a monosomic wild beet (Beta procumbens) chromosome fragment in Beta vulgaris, two complete LTR retrotransposons were identified. Both elements, designated Beetle1 and Beetle2, possess a coding region with genes in the order characteristic for Ty3-gypsy retrotransposons. Beetle1 and Beetle2 have a chromodomain in the C-terminus of the integrase gene and are highly similar to the centromeric retrotransposons (CRs) of rice, maize, and barley. Both retroelements were localized in the centromeric region of B. procumbens chromosomes by fluorescence in-situ hybridization. They can therefore be classified as centromere-specific chromoviruses. PCR analysis using RNA as template indicated that Beetle1 and Beetle2 are transcriptionally active. On the basis of the sequence diversity between the LTR sequences, it was estimated that Beetle1 and Beetle2 transposed within the last 60,000 years and 130,000 years, respectively. The centromeric localization of Beetle1 and Beetle2 and their transcriptional activity combined with high sequence conservation within each family play an important structural role in the centromeres of B. procumbens chromosomes.

Cytosine Methylation of an Ancient Satellite Family in the Wild Beet <b><i>Beta procumbens</i></b>

“…This might point to the importance of the cytosine methylation of the B. procumbens centromeric pEV arrays in the epigenetic characterization of the centromere. Together with the centromeric satellites pTS4 and pTS5 [Schmidt and Heslop-Harrison, 1996], and the centromeric gypsy -like retrotransposons Beetle1 and Beetle2 [Weber and Schmidt, 2009], the pEV satellite might be involved in the recruitment of CENH3.…”

“…B. procumbens has mostly submetacentric or acrocentric chromosomes (2n = 18). Similar to sugar beet, a large proportion of repetitive DNA including satellite DNAs has been characterized in B. procumbens [Schmidt and Heslop-Harrison, 1996;Dechyeva et al, 2003;Weber and Schmidt, 2009]. A prominent satellite is pEV which was first described in sugar beet [Schmidt and Metzlaff, 1991].…”

Evolution of Genome Content: Population Dynamics of Transposable Elements in Flies and Humans

“…TEs have been co-opted to play key organismic functions, such as the generation of antibody diversity in the vertebrate immune system (19) and maintenance of telomeres in Drosophila (134) and centromeres in plants (135,136). It is also quite likely that epigenetic mechanisms, such as gene silencing through methylation or RNAi epigenetic mechanisms evolved as a means of genomic defense against TEs and later were used to regulate host genes.…”

Integration of cytogenetic and genetic linkage maps of Lotus japonicus, a model plant for legumes

“…Note that the RIRE7 and CRM elements share more than 80% homology to LjRE2 in TM0052 (DDBJ ID: AP004525). This element has also homology to the pericentromeric repeat spread through dicotyledonous to monocotyledonous plants (Nagaki et al 2004;Weber and Schmidt 2009).…”