Retrotransposon Tf1 induces genetic adaptation to environmental stress

Authors

• C Esnault
• HL Levin

Abstract

Schizosaccharomyces pombe possesses a compact genome that tightly restricts retrotransposon expression under normal growth conditions. However, when retrotransposon Tf1 is expressed it integrates into promoters of RNA Pol II transcribed genes and in many cases this increases transcription of adjacent genes. This result together with the Tf1 preference for stress response promoters led to the idea that Tf1 could be beneficial to its host by creating a pool of new alleles necessary for the host to survive changing environmental conditions. We tested this hypothesis by studying the Tf1 response to a stress such as exposure to cobalt, and studying the fitness of cells with genomic insertions of Tf1 when exposed to cobalt. Diverse cultures containing Tf1 integrated at 25,000 positions were grown competitively in cobalt. Cells with Tf1 at 141 positions greatly increased in proportion suggesting that these integrations improved growth in cobalt. Analysis of these positions and reconstruction of strains with single insertions indicate Tf1 integration improved growth in cobalt by inducing key regulators of the TOR pathway. These results provide strong evidence that retrotransposons have the potential to promote evolution, as well as identified mechanisms that mitigate the toxicity of cobalt.

Scientific Focus Area: Genetics and Genomics

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