Origins of lineage-specific elements via gene duplication, relocation,
and regional rearrangement in Neurospora crassa
Abstract
The origin of new genes has long been a central interest of evolutionary
biologists. However, their novelty evades reconstruction by the
classical tools of evolutionary modeling. This evasion of insight from
deep ancestral investigation necessitates intensive study of model
species within well-sampled, recently diversified, clades. One such
clade is the model genus Neurospora, members of which lack recent
gene duplications, yet harbor clusters of lineage-specific genes (LSGs)
adjacent to the telomeres. Several Neurospora species are
comprehensively characterized organisms apt for studying the evolution
of LSGs. Using gene synteny, we documented that 78% of
Neurospora LSGs clusters are located in chromosomal regions
featuring extensive tracts of non-coding DNA and duplicated genes. Here
we report several instances of LSGs that are likely from regional
rearrangements and potentially from gene rebirth. To broadly investigate
functions of LSGs, we assembled transcriptomics data from 68
experimental data points and identified co-regulatory modules using
Weighted Gene Correlation Network Analysis, revealing that LSGs are
widely but peripherally involved in known regulatory machinery for
diverse functions. The ancestral status of mas-1 and its
neighbors was investigated in detail, suggesting that it arose from an
ancient lysophospholipase precursor that is ubiquitous in lineages of
the Sordariomycetes; mas-1 plays a role in cell-wall integrity
and cellular sensitivity to antifungal toxins. Our discoveries
illuminate a “rummage region” in the N. crassa genome that
enables formation of new genes and functions to arise via gene
duplication and relocation, followed by fast mutation and recombination
facilitated by tandem repeats and deconstrained non-coding sequences.