Transposable Elements and Genome Size Variations in Plants

초록

Although the number of protein-coding genes is not highly variable between plant taxa, the DNA content in their genomesis highly variable, by as much as 2,056-fold from a 1C amount of 0.0648 pg to 132.5 pg. The mean 1C-value in plants is 2.4pg, and genome size expansion/contraction is lineage-specific in plant taxonomy. Transposable element fractions in plantgenomes are also variable, as low as ~3% in small genomes and as high as ~85% in large genomes, indicating that genomesize is a linear function of transposable element content. Of the 2 classes of transposable elements, the dynamics of class 1long terminal repeat (LTR) retrotransposons is a major contributor to the 1C value differences among plants. The activity ofLTR retrotransposons is under the control of epigenetic suppressing mechanisms. Also, genome-purging mechanisms havebeen adopted to counter-balance the genome size amplification. With a wealth of information on whole-genome sequencesin plant genomes, it was revealed that several genome-purging mechanisms have been employed, depending on plant taxa. Two genera, Lilium and Fritillaria, are known to have large genomes in angiosperms. There were twice times of concertedgenome size evolutions in the family Liliaceae during the divergence of the current genera in Liliaceae. In addition to the LTRretrotransposons, non-LTR retrotransposons and satellite DNAs contributed to the huge genomes in the two genera bypossible failure of genome counter-balancing mechanisms.

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