RT Journal
A1 Tusso, Sergio
A1 Suo, Fang
A1 Liang, Yue
A1 Du, Li-Lin
A1 Wolf, Jochen B.W
T1 Reactivation of transposable elements following hybridization in fission yeast
JF Genome Research 
JO Genome Research 
YR 2021 
FD December 14 
DO 10.1101/gr.276056.121 
SP gr.276056.121 
UL http://genome.cshlp.org/content/early/2021/12/10/gr.276056.121.abstract 
AB Hybridization is thought to reactivate transposable elements (TEs) that were efficiently suppressed in the genomes of the parental hosts. Here, we provide evidence for this 'genomic shock hypothesis' in the fission yeast Schizosaccharomyces pombe. The species is characterized by divergence of two ancestral lineages (Sp and Sk) which have experienced recent, likely human induced, hybridization. We used long-read sequencing data to assemble genomes of 37 samples derived from 31 S. pombe strains spanning a wide range of ancestral admixture proportions. A comprehensive TE inventory revealed exclusive presence of long terminal repeat (LTR) retrotransposons. In-depth sequence analyses of active full-length elements, as well as solo-LTRs, revealed a complex history of homologous recombination. Population genetic analyses of syntenic sequences placed insertion of many solo-LTRs prior to the split of the Sp and Sk lineages. Most full-length elements were inserted more recently after hybridization. With the exception of a single full-length element with signs of positive selection, both solo-LTRs, and in particular, full-length elements carried signatures of purifying selection indicating effective removal by the host. Consistent with reactivation upon hybridization, the number of full-length LTR retrotransposons, varying extensively from zero to 87 among strains, significantly increased with the degree of genomic admixture. This study gives a detailed account of global TE diversity in S. pombe, documents complex recombination histories within TE elements and provides evidence for the ‘genomic shock hypothesis’ with implications for the role of TEs in adaptation and speciation.