The Genetic Transformation Of Mushrooms

Peter Flegg

We acknowledge, with thanks, permission to reproduce this article from the Mushroom Journal No. 613 of February 2001

Arousing Strong Feelings

A subject guaranteed to arouse strong feelings is that of genetically modified crops. A good starting point for us perhaps, is that, at present, there are no genetically modified mushroom strains commercially available. It is, however, very likely that at some time in the not too distant future there could be. Several research groups are working in that direction and recent progress, after a slow start, has been encouragingly rapid. So marked has been the progress in the past few months that several international mushrom journals have carried articles explaining what is meant by genetic transformation and discussing the possible benefits and dangers.

What is genetic transformation?

Genetic transformation involves transferring genes both within species and between different species and differs from the mixing of genes that occurs normally during sexual reproduction. It can dramatically speed up the production of new strains or varieties. Terms such as ‘genetic engineering’, ‘genetic modification’ and ‘recombinant DNA technology’ are also used to describe the process. The products of the use of this technology are called ‘genetically modified organisms’ or ‘GMOs’. One of those articles I referred to in the last July issue, that by Horgan and Castle in Mushroom News (No 48 (7)) and which had been presented at the 1999 North American mushroom Conference, gave seven crops as being on the Canadian list of approved GM plants including corn, potatoes and tomatoes. It also presented a table of nearly seventy ornamental plants, trees and fungi that were, at the time, being trialled for later production. It pointed out also that more than half of those in their list was of lesser commercial value than the cultivated mushroom. Another article (Webster, The Spawn Run, December 2000) recorded that in South Africa there have been over one hundred field trials and that, now, two GM crops are permitted and grown. They are insect-resistant yellow maize and insect-resistant cotton.

Why the delay with mushrooms?

If so many crops have GM strains or varieties approved for cultivation and, indeed, making up significant proportions of the total acreage grown in North America, why are there no GM mushroom strains? Well, you can be sure that it is not because mushroom geneticists and breeders have been dragging their feet. Surely, the recent article by Anton Sonnenberg (Mushroom Journal No. 608) should have disproved that idea. No doubt about it, the mushroom, Agaricus bisporus, is a difficult organism to work with. I didn’t have to be told that, I learnt it over many years of research experience, but it is not difficult to find similar expressions of frustration in the literature. For example, the first sentence of the first paper in Mushroom Science 14, the Proceedings of the International Congress held in Oxford, 1995, reads ‘Agaricus bisporus has gained a reputation as a difficult organism to manipulate through breeding’. The paper is by Loftus, Lodder and Legg of the Amycel/SpawnMate Bio Technical Group Research Laboratory in California and is a review of mushroom breeding in the mid 1990s. Among other developments, they record that transformation techniques used with other fungi are being adapted for use by the mushroom scientists and report a Dutch claim of A. bisporus having being transformed. Mushroom Science 14 also includes a paper by Elliott and colleagues from HRI and Cranfield University on the use of a compressed air gun as a means of delivering transforming DNA to mushroom cells.

Transformations: one achieved – another needed.

Five years on and it appears that the promise of really new and much improved mushroom strains is a real possibility. Sonnenberg in his keynote address to the 15th International Congress in Maastricht last year (Mushroom Science 15 and Mushroom Journal No. 608) reviewed recent developments in genetics and breeding of A. bisporus and concluded that all the prerequisites for the development of new strains have now been met. He does warn, though, that some time may yet occur between the promise of a ‘soon release’ of new strains and their actual appearance on the market. Among the prerequisites listed by Sonnenberg is efficient breeding methods, or ‘tools to do the job’, and among these he includes genetic transformation. He goes on to point to another paper presented at that Congress by himself and his colleagues, (Mikosch, Lavrijssen, Sonnenberg and Van Griensven) which describes a system based on the use of a common soil bacterium and plant pathogen, Agrobacterium tumefaciens, which they have developed with an efficient method of transforming the mycelium of A. bisporus. Also at the same Congress, HRI scientists (Challen et al., Mushroom Science 15) discussed their experiments on transforming A. bisporus, including the use of Agrobacterium tumefaciens, and concluded that, while other systems have proved unreliable, the one based on A. tumefaciens yielded stable transformants. As those who attended the HRI Mushroom Day a few months later learned, work on developing that transformation system is progessing well. At last we are on our way. A powerful biological tool is now available to mushroom geneticists and breeders. However, reaching this far has proved difficult enough, gaining acceptance of the consumer of GM mushrooms could be no less difficult. A transformation of customer perception may be needed.

The good news

As no GM mushroom strains yet exist, for the benefits from the new technology we have, initially at least, to look at what has happened with those other crops. Among the claimed benefits listed by Horgan and Castle (Mushroom News No. 38(7)) and Webster (The Spawn Run, December 2000) are pest and disease resistant crops and drought tolerance so reducing production costs and increasing the economic yield. Both articles point out that many of the benefits relate to crop producers and processors, but some consumer benefits are mentioned such as delayed ripening of tomatoes with enhanced flavour and crops with improved fat composition for healthier eating. Webster, writing about South African conditions, draws attention to major benefits for crop producers in developing countries helping the economic growth of small-scale producers and increasing the food supply for the population. Also mentioned is the possibility of using GM technology as a research tool to study the biology of the mushroom. New strains need not necessarily be an outcome of this work, but we could discover the function of some mushroom genes of which, at present we are completely in the dark. This point is particularly emphasised by Sonnenberg. Other possible and promised benefits which might accrue to the mushroom industry include, not surprisingly, pest and disease resistance and more efficient use of compost by the mushroom. Eyebrow-raising possibilities for use in niche markets are mushroom strains that are garlic flavoured or even almond flavoured! At this stage of things it looks as though listing possible attributes of new mushroom strains is just another version of ‘think of a number’.

The other side of the coin

The articles by Sonnenberg, by Horgan and Castle, and by Webster all recognise the opposition to GM foods, which exists among much of the general public. Horgan and Castle explain that worldwide there is a considerable variation. In 1999 the United Nations drafted a Biosafety Protocol which included the transfer, handling and use of ‘living modified organisms’. Two main groups of countries seem to have emerged. One group including USA, Canada, Australia, Uruguay, Argentina and Chile supports the development and use of GM plants whereas China and many developing countries are opposed to the idea. EU countries generally, they report, have sided with the opposition. At this point it is only fair to point out that the UK-based HRI, partially funded by the government money, issued a statement recently declaring that it supports GM technologies and, while recognising the benefits and potential risks, is looking to maximise the benefits and eliminate the risks. Dutch scientists are also in the fore-front of work on GM mushrooms. It seems more than likely that the ‘for and against’ situation is much more complicated than ‘some countries for and some against’! Horgan and Castle also tell us that there appear to be two main areas of concern, that of dangers to human health and that of threats to the environment. There are fears that the escape of genetically engineered traits will escape into weeds and there will be reduction in biodiversity and organically grown crops will be compromised.

What about the Consumer?

Sonnenberg points out that consumer acceptance of GM products is not helped by the general perception that the benefits accruing from the use of such crops are mainly for the crop producers and processors. The consumer seems to be gaining very little directly. Thinking about it briefly, ‘buy this product it is going to make me rich,’ does not seem to be a very appealing slogan to the customer. In similar vein Horgan and Castle pose the question, ‘why is genetic engineering more widely accepted in medicine than it is in agriculture?’ While accepting that the answer is complex, they suggest that one important fact or is that the main beneficiary is seen to be the consumer – the patient. There is probably a message there. It seems that we have passed the stage at which the question ‘who is right?’ is relevant. Those who wish to further the cause of GM crops need, perhaps, to realise those words of reassurance, however soundly-based, are unlikely to convince. We have, after all, had too many food scares in recent years. It is important that all concerns, justified or otherwise, are addressed seriously, effectively, patiently and sympathetically. It is no good going on about ’emotive issues and media hysteria,’ If the benefits from the use of GM crops are going to be as good as some claim, it has surely got to be worth the effort to confront the problems and to persuade. At the same time, don’t forget the ultimate consumers. What will be in it for them? Perhaps, when they become available, GM mushrooms should have some obvious benefits for the consumer. Mushroom breeders might like to cogitate on that. I’m not sure about peppermint flavoured mushrooms, though!