Horizontal gene transfer

A couple of recent papers are providing good evidence for the horizontal transfer of genetic material between species.

In the Journal Nature this week: A role for host–parasite interactions in the horizontal transfer of transposons across phyla.

The horizontal transfer (HT) of genetic material between non-mating species, common in bacteria, is increasingly being recognized as a significant force in eukaryotic evolution. Most instances of HT described so far in metazoans involve mobile genetic elements — mainly transposons — but the mechanisms enabling this exchange between widely divergent species are unknown. Gilbert et al. now show that transposable elements spread between disparate species by hitch-hiking in the genomes of parasites shared by these species. Specifically, Rhodnius prolixus, an insect that feeds on the blood of tetrapods and which is the vector of Chagas disease in humans, carries four distinct transposon families in its genome that can invade the genomes of a range of tetrapods including the opossum and squirrel monkey. One of these transposon families is also present in the pond snail Lymnaea stagnalis, a vector of trematodes infecting many vertebrates.

A paper in Nature earlier this year revealed that horizontal gene transfer has also been important in the evolution of virulence in Fungi: Comparative genomics reveals mobile pathogenicity chromosomes in Fusarium

Fungi of the genus Fusarium are important plant pathogens, causing various blights, root rots and wilts. While some species have a wide host range, others are more selective. Comparative genomics of three Fusarium fungi with broad and narrow host range, two newly sequenced, provide clues as to what drives these differences. Experimental follow-up shows that simply by mixing two strains on standard growth medium, transfer of two whole chromosomes from a Fusarium oxysporum tomato pathogen turns a nonpathogenic strain into a pathogenic one. These findings shed light on the evolution of host range and pathogenicity.