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Abstract BackgroundDNA transposable elements are mobilized by a “cut and paste” mechanism catalyzed by the binding of one or more transposase proteins to terminal inverted repeats (TIRs) to form a transpositional complex. Study of the rice genome indicates that themPingelement has experienced a recent burst in transposition compared to the closely relatedPingandPongelements. A previously developed yeast transposition assay allowed us to probe the role of both internal and terminal sequences in the mobilization of these elements. ResultsWe observed thatmPingand a syntheticmPongelement have significantly higher transposition efficiency than the related autonomousPingandPongelements. Systematic mutation of the internal sequences of bothmPingandmPongidentified multiple regions that promote or inhibit transposition. Simultaneous alteration of single bases on bothmPingTIRs resulted in a significant reduction in transposition frequency, indicating that each base plays a role in efficient transposase binding. Testing chimericmPingandmPongelements verified the important role of both the TIRs and internal regulatory regions.Previous experiments showed that the G at position 16, adjacent to the 5′ TIR, allows mPingto have higher mobility. Alteration of the 16th and 17th base frommPing’s3′ end or replacement of the 3′ end withPong3′ sequences significantly increased transposition frequency. ConclusionsAs the transposase proteins were consistent throughout this study, we conclude that the observed transposition differences are due to the element sequences. The presence of sub-optimal internal regions and TIR bases supports a model in which transposable elements self-limit their activity to prevent host damage and detection by host regulatory mechanisms. Knowing the role of the TIRs, adjacent sub-TIRs, and internal regulatory sequences allows for the creation of hyperactive elements.
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Independent evolution of transposase and TIRs facilitated by recombination between Mutator transposons from divergent clades in maize
Nearly all eukaryotes carry DNA transposons of the Robertson’s Mutator ( Mu ) superfamily, a widespread source of genome instability and genetic variation. Despite their pervasive impact on host genomes, much remains unknown about the evolution of these transposons. Transposase recognition of terminal inverted repeats (TIRs) is thought to drive and constrain coevolution of MuDR transposase genes and TIRs. To address the extent of this relationship and its impact, we compared separate phylogenies of TIRs and MuDR gene sequences from Mu elements in the maize genome. Five major clades were identified. As expected, most Mu elements were bound by highly similar TIRs from the same clade (homomorphic type). However, a subset of elements contained dissimilar TIRs derived from divergent clades. These “heteromorphs” typically occurred in multiple copies indicating active transposition in the genome. In addition, analysis of internal sequences showed that exchanges between elements having divergent TIRs produced new mudra and mudrb gene combinations. In several instances, TIR homomorphs had been regenerated within a heteromorph clade with retention of distinctive internal MuDR sequence combinations. Results reveal that recombination between divergent clades facilitates independent evolution of transposase ( mudra ), transposase-binding targets (TIRs), and capacity for insertion ( mudrb ) of active Mu elements. This mechanism would be enhanced by the preference of Mu insertions for recombination-rich regions near the 5′ ends of genes. We suggest that cycles of recombination give rise to alternating homo- and heteromorph forms that enhance the diversity on which selection for Mu fitness can operate.
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- Award ID(s):
- 1748105
- PAR ID:
- 10461745
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 120
- Issue:
- 31
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2305298120
