Massive Horizontal Gene Transfer in Amphioxus Illuminates the Early Evolution of Deuterostomes

Abstract

AbstractBackgroundHorizontal gene transfer (HGT) enables novel gene establishment, has frequently reported in the genomes of protostomes but rarely in that of deuterostomes. As one of the closest living invertebrate relatives of vertebrates, amphioxus is considered as an important group for the evolutionary study of vertebrates and deuterostomes.ResultsIn this study, a high-quality genome of amphioxus wasde novoassembled and annotated. Using the genomes of four amphioxi, massive HGT events were identified and introduced novel genes in different functional groups such as follows. Innate immunity of amphioxi that has no adaptative immune system was enriched by HGT genes including that for a group of lipoxygenases and a DEAD-box helicase. Anaerobic adaptation of amphioxi may have been enabled by the HGT of genes for alcohol dehydrogenase and ferredoxin. A proximally arrayed cluster of EF-hand calcium-binding protein genes similar to that of bacteria, of which the copy number was linearly correlated to the sea salinity of the collection region, may foster their survival at different calcium concentrations.ConclusionsMassive HGT events were involved in a range of amphioxus adaptations such as innate immunity, anaerobic adaptation, and calcium balance. Combining phylogenetic analysis and conservation among species, the comprehensive analysis revealed the neglected roles of HGT in the early genome evolution of vertebrates and deuterostomes.