The Drosophila TART transposon manipulates the piRNA pathway as a counter-defense strategy to limit host silencing

Abstract

Co-evolution between transposable elements (TEs) and their hosts can be antagonistic, where TEs evolve to avoid silencing and the host responds by reestablishing TE suppression, or mutualistic, where TEs are co-opted to benefit their host. The TART-A TE functions as an important component of Drosophila telomeres, but has also reportedly inserted into the D. melanogaster nuclear export factor gene nxf2. We find that, rather than inserting into nxf2, TART-A has actually captured a portion of nxf2 sequence. We show that Nxf2 is involved in suppressing TART-A activity via the piRNA pathway and that TART-A produces abundant piRNAs, some of which are antisense to the nxf2 transcript. We propose that capturing nxf2 sequence allowed TART-A to target the nxf2 gene for piRNA-mediated repression and that these two elements are engaged in antagonistic co-evolution despite the fact that TART-A is serving a critical role for its host genome.