The “evol” is in the details: a rummage-region model for the 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, 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. The model
Neurospora species—which lack recent gene duplications yet
harbor clusters of lineage-specific genes (LSGs) adjacent to the
telomeres—constitute comprehensively characterized organisms apt for
studying the evolution of LSGs. Using gene syntenies, we documented that
78% of Neurospora LSGs clusters accompany large non-coding regions,
frequent gene duplications and relocation, or regional rearrangements.
Ancestral status of the LSG mas-1 and its neighbors was
investigated in detail, and we identified sequence conservation among
syntenic non-coding regions that suggests that it arose from an ancient
copy of a lysophospholipase precursor that is ubiquitous in lineages of
the Sordariomycetes. High resistance to polyoxin D of the mas-1
mutant demonstrates that the gene exhibits a role in cell-wall integrity
and cellular sensitivity to antifungal toxins. To perform a broader
investigation of the function of LSGs, we assembled transcriptomics data
from 68 experimental data points and identified co-regulatory modules
using Weighted Gene Correlation Network Analysis. This analysis revealed
no essential roles for LSGs in known regulatory machinery. Our
discoveries illuminate a “rummage region” in the N. crassa
genome that enables some novel elements and new functions to arise via
gene duplication and relocation or invasion of genetic materials,
followed by fast mutation and recombination facilitated by tandem
repeats and unconstrained non-coding sequences.