GMO mushrooms

June 2016
Photo: button mushrooms. Adam Fagen on Flickr
As if to illustrate how simple the latest technique for gene modification is, it seems likely that Americans will be eating 'CRISPR/Cas9' [1] gene-edited 'anti-browning' mushrooms within a couple of years.

Creating a GMO using CRISPR/Cas9 "needs little training and nothing too fancy or expensive in the way of laboratory equipment" [1].  It is "fast, cheap and easy" (Hall), and has just been made faster, cheaper and easier by the US Department of Agriculture (USDA).

The GM mushrooms were created by Professor Yinong Yang, a plant pathologist in Pennsylvania State University, who had no prior expertise in mushrooms except "how to eat them".  Yet, after turning his attention to the project in 2013, only about two months of labwork were needed to achieve the required GMO.  Conveniently, mushrooms grow to maturity in only five weeks and can be grown year-round in climate-controlled facilities.  The 'field trials' were completed in a matter of months, and by October 2014, Prof. Yinong Yang was ready to present his idea to the USDA.

Regulation of the GM mushrooms seems to have consisted of an informal talk to a small group of  APHIS* regulators.  All the Prof had to do was explain why no regulation was needed for his "trait improvement" using CRISPR/Cas9 mediated "precision breeding" (in which no breeding is actually involved [2]).

A few months later, the USDA waved the mushrooms through.

In the meantime, while Prof Yinong Yang was reported to be mulling over whether to start a company to commercialize his modified mushrooms, the commercialization machine was already going full-steam-ahead.  The necessary patent had been applied for.  Pennsylvanian mushroom growers had been given a "continuing education seminar on mushrooms", during which the $3 million prizes presented to CRISPR's inventors by actress, Cameron Diaz, were showcased with photographs of pristine GM mushrooms alongside old-fashioned brown, decaying ones. .

Although no food safety approval is needed, Yinong Yang plans to seek voluntary approval from the Food and Drug Administration (FDA) to cover his back.

Mushrooms are big business, and the US $1.2 billion mushroom market is dominated by Pennsylvania.  Growing them is easy, but harvesting and handling require extreme care due to their speedy decay if bruised.  Their shelf-life is short, and their usable time-frame once sliced is extremely short.  Yinong Yang's anti-browning mushrooms have 30% less discolouration, which improves their appearance (saleability) and shelf-life.  They will facilitate mechanical harvesting thus saving time and effort, and will reduce waste.

To create these magic mushrooms, multiple small sections were excised from one of the genes which triggers browning in response to physical insult.  The CRISPR/Cas9 construct which achieved this feat consisted of two elements copied from E.coli (a bacterial pathogen of animals), one element copied from Strep. pyogenes (a bacterial pathogen of animals), one element copied from Agrobacterium tumefaciens (a bacterial pathogen of plants), plus three synthetic elements, and a mushroom DNA promoter to produce the guide molecule needed to find the right bits of the gene to be snipped out.

Tests were made to make sure none of these CRISPR/Cas9 sequences had been incorporated into the mushroom genome by mistake, after which  "Genome-edited mushroom strains containing no foreign DNA integration were selected for further studies and potential commercialization".


That last statement comes from Prof Yinong Yang's official letter of enquiry to APHIS.  It suggests that much of the outcome of CRISPR/Cas9 "precision breeding" which isn't breeding is prone to the same spurious scrambling of DNA as all the previous non-precision non-breeding techniques.

The assumption that assaulting a genome with elements of pathogenic and synthetic DNA plus unfettered gene promoters will not leave a trail of functional disruption in their wake, even if no remaining bits of artificial DNA have been detected, isn't good science.

Fungi produce some of the most toxic substances known to man.  White button mushrooms contain a number of toxins, including one carcinogen, and cooking before eating is recommended to destroy these.  The assumption that the CRISPR/Cas9 genomic assault can't trigger or enhance toxin formation by the mushrooms isn't good science.

Subtle changes in mushroom physiology can lead to significant changes in microbial colonisation.  Commercial mushroom farms grow their crops in horse or chicken manure, which will always be a potential source of pathogens.

The functional genome forms a highly interactive whole: if you disable one gene, others will change to compensate.  No one's asked why mushrooms evolved to brown easily in the first place: is it an immune mechanism to keep pathogens at bay?  If so, the aged mushrooms genetically disguised as freshly-picked and freshly-prepared specimens could be bad news for vulnerable people.

In truth, the 'precision' of gene editing does not mean predictable or error-free outcomes.

Make sure Europe doesn't fall for the schoolboy version of genetics and gene editing crafted by corporate PR departments.

[1]  CRISPR/Cas9 GENEEDITING - March 2016

*APHIS is the USDA Animal and Plant Health Inspection Service.  It's mission is "to protect the health and value of American agriculture and natural resources", with special reference to invasive pests and pathogens, and protection of exports.  Beyond this, human health and safety are not its business.


  • Stephen S. Hall, Editing the Mushroom, Scientific American, March 2016
  • Katherine Derla, CRISPR-edited button mushroom bypasses GMO food rules: USDA explains why,, 18.04.16
  • Jonathan Latham, God's Red Pencil? CRISPR and The Three Myths of Precise Genom
  • Editing, Independent Science News, 25.04.16
  • Are raw mushrooms toxic?, accessed May 2016
  • Agaritine, Wikipedia, accessed May 2016
  • Emily Waltz, 2016, Gene-edited CRISPR mushroom escapes US regulation, Nature 532
  • Douglas Main, Genetically altered mushroom cleared by the USDA, Europe Newsweek, 19.04.16
  • Letter from Professor Yinong Yang to APHIS, 30.10.15

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