Active miniature transposons from a plant genome and its non-recombining Y chromosome
Roberta Bergero 1*, Alan Forrest 1 and Deborah Charlesworth 1
1 University of Edinburgh
* To whom correspondence should be addressed. E-mail: r.bergero{at}ed.ac.uk.
Submitted on October 18, 2007
Revised on November 30, 2007
Accepted on 16 December 2007
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Abstract |
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Mechanisms involved in eroding fitness of evolving Y-chromosomes have been the focus of much theoretical and empirical work. Evolving Y-chromosomes are expected to accumulate transposable elements (TEs), but it is not known whether such accumulation contributes to their genetic degeneration. Among TEs, miniature inverted-repeat transposable elements are non-autonomous DNA transposons, often inserted in introns and untranslated regions of genes. Thus, if they invade Y-linked genes and selection against their insertion is ineffective, they could contribute to genetic degeneration of evolving Y-chromosome. Here, we examine the population dynamics of active MITEs in the young Y-chromosomes of the plant Silene latifolia and compare their distribution with those in recombining genomic regions. In order to isolate active MITEs, we developed a straightforward approach based on the assumption that recent transposon insertions or excisions create singleton or low-frequency size-polymorphisms which can be detected in alleles from natural populations. Transposon display was then used to infer the distribution of MITE insertion frequencies. The overall frequency spectrum showed an excess of singleton and low-frequency insertions which suggest that these elements are readily removed from recombining chromosomes. In constrast, insertions on the Y-chromosomes were present at high frequencies. Their potential contribution to Y-degeneration is discussed.
Key Words:
TE dynamics, genome evolution, non-recombining chromosomes, repetitive DNA, transposon display
