A mutation in DNA polymerase γ harbours a shortened lifespan and high sensitivity to mutagens in the filamentous fungus Neurospora crassa

Abstract

A novel short lifespan mutant in N. crassa was screened and analyzed to better understand the mechanism involved in maintaining hyphal elongation in filamentous fungi. The mutant strain exhibited a reduced number of possible conidia passages and a shorter hyphal elongation limit. In addition, the mutant strain exhibited higher sensitivity to mutagens such as hydroxyurea (HU) and ultraviolet (UV) radiation. Based on these observations, we named the novel mutant "mutagen sensitive and short lifespan 1 (ms1)". The mutation responsible for the short lifespan and mutagen sensitivity in the ms1 strain was identified in DNA polymerase γ (mip-1:NCU00276). This mutation presumably changed the amino acid at position 814 in the polymerase domain from leucine to arginine (MIP-1 L814R). mtDNA depletion was observed in the ms1 strain, indicating that the mutation in mip-1 caused mtDNA instability. Furthermore, copy numbers for specific regions of mtDNA were preferentially decreased in the ms1 strain, and these regions were found to be near GC-rich hairpins or clusters of putative G-quadruplex sequences . These secondary structures in DNA sequences, along with HU and UV damage, can impede the progression of the replication fork. This suggests that MIP-1 L814R is more vulnerable to replication stresses than wild-type MIP-1. Our findings highlight the importance of stable mtDNA replication for continuous hyphal elongation and demonstrate that aberrant replication can shorten the lifespan of filamentous fungi.journal articl