A recently evolved nonautonomous DNA transposon shapes DREB-related DRF1 gene architecture in Triticeae

A nonautonomous DNA transposon was identified within the dehydration responsive factor 1 (DRF1) gene, a member of the DREB (dehydration responsive element binding) family involved in abiotic stress responses. The element was first detected in the Triticum durum TdDRF1 locus and subsequently in homologous genes from T. aestivum and its progenitors, T. urartu, Aegilops speltoides, and A. tauschii. The DRF1 gene consists of four exons and three introns, with the transposon inserted between Intron 1 and Intron 3. The element exhibits characteristic signatures of DNA transposons, including terminal inverted repeats (TIRs), target site duplications, and multiple internal direct and inverted repeats. Based on TIR organization, we propose a putative mechanism for its integration. Because no transposase‑coding region was detected, the element is classified as nonautonomous. We hypothesized-as a working model and a plausible evolutionary scenario-that transposable-element activity contributed to the reconstruction of DRF1 architecture, together with the potential involvement of nonsense-mediated decay/RNA interference pathways. The transposon carries a conserved core element composed of Exon 2, Intron 2, and Exon 3, which participate in alternative splicing of DRF1. Comparative and phylogenomic analyses reveal that an intact transposon is restricted to Triticeae, whereas earlier diverging Poaceae retain only degraded remnants of the core element. No comparable insertion or splice variants were detected in dicots such as Arabidopsis thaliana, indicating a monocot‑specific evolutionary event. These results suggest that a recently evolved nonautonomous transposon contributed to structural diversification and alternative splicing of DRF1 in grasses, highlighting the broader role of transposable elements in shaping gene regulation and genome evolution in Triticeae.