THE IMPACT OF TWO ABUNDANT TRANSPOSABLE ELEMENT
FAMILIES ON GENOME DIFFERENTIATION IN POLYPLOID
WHEAT
E.M. Sergeeva*, I.G. Adonina, A.B. Shcherban, E.A. Salina
Institute of Cytology and Genetics SB RAS, Novosibirsk, Russia
e-mail: sergeeva@bionet.nsc.ru
*Corresponding author
Key words: transposable element, DNA-transposon Caspar, LTR-retrotransposon
Fatima, Triticum, Aegilops
Motivation and Aim: The bread wheat Triticum aestivum is allohexaploid (BBAADD,
2n = 6x = 42) with genome size 16×109 base pairs. The complete genomic sequence of
this species is still unknown. According to different estimations, transposable element
(TE) families of different abundance account for 60-70% of the wheat genome. TEs are
likely to influence considerably the differentiation of genomes in the allopolyploid
nucleus. The analysis of genomic organization and phylogenetic relationships of
different TE families will allow us to make the inferences about evolution of genomes
in the polyploid wheat and its diploid relatives. We took into analysis two TE families
abundant in the wheat genome which belong to the TE classes with differing
mechanisms of transposition: DNA-transposon Caspar and LTR-retrotransposon
Fatima.
Methods and Algorithms: We combined two approaches: the phylogenetic analysis of
the TE copies available in databases, and fluorescent in situ hybridization to the
Triticum and Aegilops metaphase chromosomes to explore the chromosomal
distribution of the TEs. The public nucleotide database mining for the TE sequences
was conducted using consensus nucleotide sequences coding for transposase (for the
DNA-transposon) or polyprotein (the LTR-retrotransposon) with BLASTn algorithm.
The multiple nucleotide sequence alignments were performed by the ClustalW program;
phylogenetic trees were constructed using the neighbor-joining method by the MEGA4
software package.
Results: We found the DNA-transposon Caspar to be localized predominantly in the
subtelomeric chromosomal regions of the bread wheat and its diploid relatives. The
LTR-retrotransposon Fatima is localized mainly on the chromosomes belonging to the
В-genome of the polyploid wheats and on those of Aegilops speltoides (presumable
donor of the genome B). The phylogenetic analysis showed that both the TE families
formed distinct genome- and species-specific groups and their proliferation in genomes
mainly took place during the divergence of the diploid Triticum and Aegilops species.
Conclusion: We demonstrated the impact of the DNA-transposon Caspar to the
formation and differentiation of the subtelomeric chromosomal regions of different
genomes in the polyploid wheat; and the impact of the LTR-retrotransposon Fatima to
the differentiation of the B-genome of the polyploid wheats. Our results point the
important role of the TE families in structuring and evolution of grass genomes.
Acknowledgements. We thank the Russian Foundation for Basic Research (08-0400307) for financial support.