Emphasis Type="Italic"MuTAnT/Emphasis a famil

Authors: Krzysztof Stawujak Michał Startek Anna Gambin Dariusz Grzebelus

Publish Date: 2015/05/17

Volume: 143, Issue: 4, Pages: 433-440

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Abstract

Transposable elements TEs are mobile DNA segments abundant and dynamic in plant genomes Because their mobility can be potentially deleterious to the host a variety of mechanisms evolved limiting that negative impact one of them being preference for a specific target insertion site Here we describe a family of Mutatorlike DNA transposons in Medicago truncatula targeting TA microsatellites We identified 218 copies of MuTAnTs and an element carrying a complete ORF encoding a mudrAlike transposase Most insertion sites are flanked by a variable number of TA tandem repeats indicating that MuTAnTs are specifically targeting TA microsatellites Other TE families flanked by TA repeats eg TAFT elements in maize were described previously however we identified the first putative autonomous element sharing that characteristics with a related group of short nonautonomous transposonsTransposable elements TEs are mobile DNA segments present in most organisms In higher plants their content varies from 10  in Arabidopsis Arabidopsis Genome Initiative 2000 to more than 80  in maize Schnable et al 2009 With respect to the transposition mechanism TEs are divided into two classes class I retrotransposons transpose via an RNA intermediate while class II DNA transposons change their location by a cutandpaste mechanism characteristic for TEs carrying terminal inverted repeats TIRs or a rollingcircle mechanism typical for Helitrons Wicker et al 2007 A family of DNA transposons usually consists of one or a few autonomous elements capable of inducing their own transposition and more copies with internal deletions and rearrangements referred to as nonautonomous which lost the ability to transpose independently however they can be mobilized by a related autonomous element Wessler 2006The canonical Mutator element was discovered in a maize stocks showing a high forward mutation rate Robertson 1978 Since then many Mutatorlike elements MULEs have been identified in plants Holligan et al 2006 fungi Chalvet et al 2003 protozoans Pritham et al 2005 Lopes et al 2009 and metazoans Marquez and Pritham 2010 Autonomous MuDRlike elements carry two open reading frames mudrA and mudrB the former coding for a transposase while a function of the latter is not well defined There is also a group of Mutatorlike autonomous elements eg Jittery carrying only mudrAlike ORF Xu et al 2004Tandemly repeated motifs of 2–6 nt are commonly referred to as microsatellites Microsatellites exhibit variation in length structure frequency of individual motifs and genomic distribution Schulman et al 2005 In plants TAn repeats are more abundant compared to other dinucleotide motifs Wang et al 1994 Microsatellite regions are considered as hypervariable as the number of tandem repeats can be changed following DNA polymerase slippage in the course of DNA replication In plants tandem repeats were shown to be preferentially associated with generich regions Morgante et al 2002 In Medicago truncatula microsatellites were found near genes in 5′ and 3′ untranslated regions UTRs and introns Mun et al 2006Relationships between microsatellites and TEs were reported in insects Meglécz et al 2007 nematodes Johnson et al 2006 and plants Temnykh et al 2001 Tero et al 2006 TEs targeting microsatellites were reported in Lepidoptera Coates et al 2010 rice Akagi et al 2001 and maize Wang and Dooner 2006 Protomicrosatellites were shown to be created by Angela LTR retrotransposons in pea Smýkal et al 2009 Microsatelliteassociated interspersed nuclear elements MINEs containing hitchhiking microsatellites identified in moths Coates et al 2011 are another example of possible TEmicrosatellite relationshipsHere we report on MuTAnTs a novel family of MULEs present in M truncatula and targeting TAn microsatellite repeats We identified 218 copies of MuTAnTs and characterized a putative autonomous element carrying a complete ORF encoding a mudrAlike transposaseMolecular analyses were performed on the reference line A17 ‘Jemalong’ 2HA an A17 derivative and on 21 wild accessions of M truncatula provided by INRA Montpelier France Apart from M truncatula eight other Fabaceae species ie Lupinus angustifolius L L luteus L Pisum sativum L Phaseolus vulgaris L Trifolium pratense L T repens L and Vicia faba L were included in the analyses Additional file 1 Each accession was represented by a single plant seeds were germinated according to the Medicago Handbook Garcia et al 2006 plants were grown in pots in the greenhouse Genomic DNA was isolated from the fresh tissue collected from ca 8weeksold plants with Plant DNeasy Mini Kit Qiagen following the manufacturer’s protocol

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