Bread mold avoids infection by mutating its own DNA

Date:
June 22, 2020
Source:
University of Bath
Summary:
Whilst most organisms try to stop their DNA from mutating,
scientists from the UK and China have discovered that a common
fungus found on bread actively mutates its own DNA as a way of
fighting virus-like infections.



FULL STORY ========================================================================== Whilst most organisms try to stop their DNA from mutating, scientists
from the UK and China have discovered that a common fungus found on bread actively mutates its own DNA as a way of fighting virus-like infections.


==========================================================================
All organisms mutate all of the time. You were born with between ten and
a hundred new mutations, for example. Many do little harm but, if they
hit one of your genes, mutations are much more likely to be harmful than beneficial. If harmful enough they contribute to genetic diseases.

Whilst mutations can enable species to adapt, most mutations are harmful,
and so evolutionary biologists have postulated that natural selection
will always act to reduce the mutation rate.

While prior data has supported this view, recent work by Professor
Laurence Hurst of the Milner Centre for Evolution at the University of
Bath (UK) and Sihai Yang, Long Wang and colleagues at Nanjing University (China) have found that Neurospora crassa, a type of bread mould, is a remarkable exception to the rule.

Professor Hurst, Director of the Milner Centre for Evolution at the
University of Bath, said: "Many organisms have a problem with transposable elements, otherwise called jumping genes.

"These are virus-like bits of DNA that insert themselves into their
host's DNA, copy themselves and keep on inserting -- hence the name
jumping genes.



========================================================================== "Organisms have found different ways of combatting this nuisance, many
of which try to prevent the transposable elements from expressing their
own genes.

Neurospora has evolved a different solution: it hits them exceptionally
hard with mutations to rapidly degrade them." The study, published in
Genome Biology, found that Neurospora distinguishes jumping genes from
its own DNA by detecting two or more copies of the same bit of DNA. The
fungus then attacks the jumping genes by mutating them in a process
called Repeat-Induced Point mutation (RIP).

To understand how RIP affects the fungus's own DNA, the team sequenced
the whole genome from both parents and offspring for many strains of
Neurospora to see how many mutations could be found and where they were
in the DNA.

Overall, they found that each base pair in the Neurospora genome has
about a one in a million chance of mutating every generation; over a
hundred times higher than any non-viral life on the planet.

Professor Hurst said: "This was a real surprise to us -- any organism that
hits its own genes with that many mutations is likely one that will not
persist for very long. It would be like opening up the back of a watch, stabbing at all the cog wheels that look a bit similar and expecting the
watch to still function! "Our findings show that Neurospora has not only
a high mutation rate but is also a massive outlier. It appears to use
RIP to destroy transposable elements but at a cost, with considerable collateral damage.

"This organism thus goes against the standard theory for mutation rate evolution which proposes that selection should always act to reduce the mutational burden.

"It is the exception that proves the rule."

========================================================================== Story Source: Materials provided by University_of_Bath. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Long Wang, Yingying Sun, Xiaoguang Sun, Luyao Yu, Lan Xue, Zhen
He, Ju
Huang, Dacheng Tian, Laurence D. Hurst, Sihai Yang. Repeat-induced
point mutation in Neurospora crassa causes the highest known
mutation rate and mutational burden of any cellular life. Genome
Biology, 2020; 21 (1) DOI: 10.1186/s13059-020-02060-w ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200622133041.htm

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