Glomhopper-a subfamily of DUF3504-encoding CryptonA elements in Glomeromycota

Transposable elements drive genomic changes and are mobilized by specific nucleases. Among them are tyrosine recombinases (YRs), which mediate DNA cleavage and rejoining. YR-encoding elements, such as DIRS, Ngaro, Crypton, and Starships, occur in diverse eukaryotes and display characteristic terminal repeat structures that enable their mobility. Their activity in fungi results in large-scale chromosomal rearrangements, horizontal gene transfer, and the movement of genes for pathogenicity, symbiosis, and secondary metabolism. Other YR-elements underwent domestication giving rise to ZMYM transcriptional regulators in animals.

We identify and characterize the fungal members of the CryptonA lineage of tyrosine recombinase-encoding transposons, which we name Glomhoppers. These elements encode a DUF3504 domain that retains the conserved catalytic residues characteristic of active YRs. In contrast, many domesticated animal DUF3504 homologs lack key catalytic residues, whereas active CryptonA transposon-derived DUF3504 elements have also been reported in animals. Structural modeling suggested the presence of a putative DNA-binding groove, and phylogenetic analyses placed Glomhoppers as a well-supported subclade within the CryptonA lineage, together with domesticated ZMYM-like derivatives. Across 72 Glomeromycota genomes, ~ 1,800 Glomhopper copies were identified, representing a subset of DUF3504-containing loci, mostly truncated or intronized, but ~ 25% lacked introns and maintained intact catalytic motifs, consistent with potential mobility. Genomic context analysis revealed their frequent localization within highly repetitive compartments, often alongside other transposon families. Expression data indicated that intronless variants respond to stress, reaching several-fold higher expression levels than intron-containing forms, especially in Gigaspora species. This is consistent with the possibility that a subset of Glomhoppers remains transcriptionally active and potentially mobilizable, although direct evidence of transposition is lacking.

Our findings establish Glomhoppers as a novel subfamily of DUF3504-encoding CryptonAs. The lineage-specific distribution, intron variation, and stress-responsive expression of Glomhoppers suggest divergent evolutionary trajectories, potentially including both mobility and domestication. These elements expand the known diversity of YR transposons and highlight DUF3504 as a candidate domain for further functional and evolutionary studies.