Revealing an active mechanism of horizontal gene transfer in fungi

Current theory asserts that eukaryotic evolution is almost exclusively mediated through vertical transmission, from parent to offspring, and relegates horizontal gene transfer (HGT), the movement of genes between individuals, to an extraordinarily rare event.

In recent years, mounting evidence from high-quality genome sequencing has forced the field to consider that HGT is likely a persistent occurrence in eukaryotic evolution.

However, as no active mechanism for HGT is known in eukaryotes, the evolutionary origin of these genes remains almost entirely a mystery.

A potential vector of HGT in eukaryotes are transposable elements (TEs), parasitic genetic sequences that can replicate independently of their host genome. Recently, I discovered a novel group of TEs that are common in filamentous fungi, which I named Starships.

These elements are massive, reaching sizes over 500 kb, and carry an extreme diversity of genetic “cargo”, some with adaptive functions such as plant pathogenicity. Furthermore, evidence suggests that many Starships have undergone HGT among a diverse set of lineages. Thus, I propose that the Starships represent the first known mechanism of active HGT among eukaryotes.

I will examine this role by developing a tractable model system in which to observe HGT under laboratory conditions.

This will be done by investigating the basic biology of Starship transposition in a model fungus with the use of transposon assays that we have recently developed and used to prove that the Staships are mobile.

We will use this knowledge to design and create “donor” strains which we can pair with any recipient strain of fungus to monitor for HGT.

Lastly, we will determine if fungi utilize the movement of the Starships to adapt to their environment by assaying the impact of a Starship on the fitness of a plant pathogenic fungus.

This work will demonstrate that HGT is an active and ongoing process in eukaryotic evolution, dramatically reshaping our current views.