Abstract
Horizontal gene transfer (HGT), the movement of genetic material across branches of the tree of life, is well established in prokaryotes and uncontroversial. This is explained in part by relatively compact prokaryote genomes that facilitate assembly and gene prediction, resulting in thousands of complete genomes for analysis. By contrast, their large and often complex genome structure have thwarted HGT studies of eukaryotes. The tide has recently turned with the availability of sufficient high-quality genome data to address quantity and quality of HGT in these taxa. Here, we argue that HGT is a small but significant player in the evolution of microbial eukaryotes and provide examples where HGT has facilitated gain of adaptive functions and in some cases, underpinned major lifestyle transitions.
Horizontal gene transfer (HGT) is emerging as a significant contributor to eukaryotic genomes, challenging previous assertions that HGT is restricted to prokaryotes and only relevant to eukaryotes during organellogenesis.HGTs often confer an adaptive advantage to the ‘host’ organism, and many of these adaptations significantly enhance metabolic pathways, leading to lifestyle shifts or survival in highly fluctuating environments.Protists that exhibit a range of lifestyles, including photosynthesis, mixotrophy, polyextremophily, and parasitism, comprise the earliest divergences in major multicellular lineages, making them models for understanding the role of HGT in evolutionary transitions.HGT represents, on average, about 1% of protist gene inventories, although this ‘rule’ needs to be tested in the future using more data and a standardized pipeline for HGT quantification.