Characterization of transcriptional activation and inserted-into-gene preference of various transposable elements in the Brassica species.

Transposable elements (TEs) have attracted increasing attention because of their tremendous contributions to genome reorganization and gene variation through dramatic proliferation and excision via transposition. However, less known are the transcriptional activation of various TEs and the characteristics of TE insertion into genomes at the genome-wide level. In the present study, we focused on TE genes for transposition and gene disruption by insertion of TEs in expression sequences of Brassica, to investigate the transcriptional activation of TEs, the biased insertion of TEs into genes, and their salient characteristics. Long terminal repeat (LTR-retrotransposon) accounted for the majority of these active TE genes (70.8%), suggesting that transposition activation varied with TE type. 6.1% genes were interrupted by LTR-retrotransposons, which indicated their preference for insertion into genes. TEs were preferentially inserted into cellular component-specific genes acted as "binding" elements and involved in metabolic processes. TEs have a biased insertion into some host genes that were involved with important molecular functions and TE genes exhibited spatiotemporal expression. These results suggested that various types of transposons differentially contributed to gene variation and affected gene function.