Horizontal Gene Transfer Between Fungi and Myxozoa: An Evolutionary Perspective

Horizontal gene transfer (HGT) is increasingly recognized as an important mechanism driving evolutionary innovation in eukaryotes, yet its functional significance in highly reduced parasitic lineages remains poorly understood. Myxozoans are obligate cnidarian parasites characterized by extreme genome reduction and complex life cycles involving multiple hosts, making them an intriguing system for investigating the adaptive role of HGT. In this study, we performed a comparative genomic and transcriptomic analysis to identify and characterize candidate genes transferred from fungi to myxozoan parasites. Phylogenetic reconstruction, sequence composition analyses, and functional annotation provided multiple lines of evidence supporting ancient HGT events retained across diverse myxozoan species. The transferred genes encode proteins involved in carbohydrate metabolism, membrane transport, stress response, and regulatory processes, functions that may contribute to host–parasite interactions and parasitic adaptation. Analysis of publicly available RNA-seq datasets revealed that many candidate genes are transcriptionally active across multiple species, corroborating biological relevance. Codon usage patterns further suggest partial amelioration toward host genomic preferences while retaining signatures of their donor origin, consistent with long-term evolutionary assimilation. Molecular clock analyses indicate that the inferred fungi-to-myxozoan HGT events coincide temporally with major increases in actinopterygian and chondrichthyan richness and align with evidence for a major diversification of myxozoans around 300 Ma. Collectively, these findings support the view that horizontally acquired genes can contribute functionally to important innovations that persist over evolutionary timescales and may facilitate the success of organisms with reduced genomes and specialized parasitic lifestyles. This work provides new insights into the evolutionary impact of HGT in myxozoans and highlights the need for future functional studies to elucidate the specific roles of transferred genes in host–parasite interactions.