Horizontal Gene Transfer from Fungi to Myxozoa: Genomic Evidence and Evolutionary Implications

Horizontal gene transfer (HGT) is increasingly recognized as an important mechanism driving evolutionary innovation in eukaryotes, yet its functional significance in parasitic lineages remains poorly understood. Myxozoans are obligate cnidarian parasites characterized by extreme genome reduction and complex two-host life cycles, making them an intriguing system for investigating the evolutionary role of HGT. We conducted a comparative genomic and transcriptomic analysis to identify and characterize candidate genes putatively transferred from fungi to myxozoans. Phylogenetic reconstruction, sequence composition analyses, and functional annotation provided multiple lines of evidence supporting ancient HGT events retained across diverse myxozoan species. Candidate transferred genes encode proteins putatively involved in carbohydrate metabolism, defense, and regulatory processes. Exploratory codon-usage analysis revealed compositional differences between candidate genes and the sampled reference sets, a pattern that may be consistent with partial amelioration following ancient transfer, although broader quantitative comparisons will be required to evaluate codon adaptation more rigorously. Molecular clock analyses place the inferred fungi-to-myxozoan HGT events within a time interval that overlaps with the major diversification of myxozoans, around 300 Ma. Collectively, these findings suggest that candidate horizontally acquired genes may have contributed to functional innovation during myxozoan evolution, expanding our understanding of the evolutionary impact of HGT in these highly reduced parasites.