Diversity and structure of <it>PIF/Harbinger</it>-like elements in the genome of <it>Medicago truncatula</it>

• Main Authors: Kucherov Gregory, Gambin Tomasz, Lasota Slawomir, Grzebelus Dariusz, Gambin Anna
• Format: Article
• Language: English
• Published: BMC 2007-11-01
• Series: BMC Genomics
• Online Access: http://www.biomedcentral.com/1471-2164/8/409

<p>Abstract</p> <p>Background</p> <p>Transposable elements constitute a significant fraction of plant genomes. The <it>PIF/Harbinger </it>superfamily includes DNA transposons (class II elements) carrying terminal inverted repeats and producing a 3 bp target site duplication upon insertion. The presence of an ORF coding for the DDE/DDD transposase, required for transposition, is characteristic for the autonomous <it>PIF/Harbinger</it>-like elements. Based on the above features, <it>PIF/Harbinger</it>-like elements were identified in several plant genomes and divided into several evolutionary lineages. Availability of a significant portion of <it>Medicago truncatula </it>genomic sequence allowed for mining <it>PIF/Harbinger</it>-like elements, starting from a single previously described element <it>MtMaster</it>.</p> <p>Results</p> <p>Twenty two putative autonomous, i.e. carrying an ORF coding for TPase and complete terminal inverted repeats, and 67 non-autonomous <it>PIF/Harbinger</it>-like elements were found in the genome of <it>M. truncatula</it>. They were divided into five families, <it>MtPH-A5</it>, <it>MtPH-A6</it>, <it>MtPH-D</it>,<it>MtPH-E</it>, and <it>MtPH-M</it>, corresponding to three previously identified and two new lineages. The largest families, <it>MtPH-A6 </it>and <it>MtPH-M </it>were further divided into four and three subfamilies, respectively. Non-autonomous elements were usually direct deletion derivatives of the putative autonomous element, however other types of rearrangements, including inversions and nested insertions were also observed. An interesting structural characteristic – the presence of 60 bp tandem repeats – was observed in a group of elements of subfamily <it>MtPH-A6-4</it>. Some families could be related to miniature inverted repeat elements (MITEs). The presence of empty <it>loci </it>(RESites), paralogous to those flanking the identified transposable elements, both autonomous and non-autonomous, as well as the presence of transposon insertion related size polymorphisms, confirmed that some of the mined elements were capable for transposition.</p> <p>Conclusion</p> <p>The population of <it>PIF/Harbinger</it>-like elements in the genome of <it>M. truncatula </it>is diverse. A detailed intra-family comparison of the elements' structure proved that they proliferated in the genome generally following the model of abortive gap repair. However, the presence of tandem repeats facilitated more pronounced rearrangements of the element internal regions. The insertion polymorphism of the <it>MtPH </it>elements and related MITE families in different populations of <it>M. truncatula</it>, if further confirmed experimentally, could be used as a source of molecular markers complementary to other marker systems.</p>