Horizontal gene acquisitions by eukaryotes as drivers of adaptive evolution

Abstract

In contrast to vertical gene transfer from parent to offspring, horizontal (or lateral) gene transfer moves genetic information between different species. Bacteria and archaea often adapt through horizontal gene transfer. Recent analyses indicate that eukaryotic genomes, too, have acquired numerous genes via horizontal transfer from prokaryotes and other lineages. Based on this we raise the hypothesis that horizontally acquired genes may have contributed more to adaptive evolution of eukaryotes than previously assumed. Current candidate sets of horizontally acquired eukaryotic genes may just be the tip of an iceberg. We have recently shown that adaptation of the thermoacidophilic red alga Galdieria sulphuraria to its hot, acid, toxic-metal laden, volcanic environment was facilitated by the acquisition of numerous genes from extremophile bacteria and archaea. Other recently published examples of horizontal acquisitions involved in adaptation include ice-binding proteins in marine algae, enzymes for carotenoid biosynthesis in aphids, and genes involved in fungal metabolism. Editor's suggested further reading in BioEssays Jumping the fine LINE between species: Horizontal transfer of transposable elements in animals catalyses genome evolution Abstract.

Monophyly of Archaeplastida supergroup and relationships among its lineages in the light of phylogenetic and phylogenomic studies. Are we close to a consensus?

“…Although such genes should be excluded from phylogenetic data sets, it can be difficult to recognize hidden paralogs and separate them from real orthologs. The same problem concerns genes subjected to horizontal gene transfer (HGT), which seems to be a common process, not only in prokaryotic organisms, but also eukaryotes including Archaeplastida lineages [106][107][108][109][110][111]. Such genes are most likely also present in many alignments analyzed and could cause artificial clustering.…”

Microbial Speciation

“…This notion was extended in the biological species concept of Dobzhansky (1935) and Mayr (1942), which states that species are reproductively isolated units, implying that adaptive mutations can spread within a species leaving other coexisting species unaffected. Although recent evidence has shown that reproductive boundaries can be leaky (Danchin and Rosso 2012;Syvanen 2012;Schönknecht et al 2013), species are still regarded as congruent genetic and ecological units for sexual eukaryotes, even if hybrids and intermediate forms are common (Mallet 2008). For bacteria and archaea, however, the situation has been marred by several complicating factors that question whether such units can be defined.…”

A tale of two tardigrades

“…For us, identifying cases where transfer has amended or added function in the recipient lineage, however rare, represents one of the most exciting prospects of this field of research. Researchers are therefore correct to look for HGT in organisms that are capable of "extraordinary" biological functions, for example colonizing extreme or variant environments in contrast to related taxa (27). However, caution is needed in these endeavors.…”