Bridging the generation gap

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Arabidopsis, or rock cress, is used by scientists as a model flowering plant

A farmer can remember what has happened last year and the year before, and can prepare accordingly.  But what about plants? How can they pass on their experience to their offspring?

It turns out that they can and do, and by being prepared, the new plants will grow better than they otherwise would have.

Scientists from Warwick University have reported in the journal eLIFE that when plants were repeatedly grown in soil with a high salt content, seeds from these plants then grew better in the same difficult conditions than seeds from unstressed plants. However this is just a short-term change, as a single generation back in normal soil removes this memory.

That they can do this is not in itself new knowledge.  Lead scientist Jose Guttierez-Marcos said, “It’s well known that plants have to adapt to environmental fluctuations using this strategy, which in the past used to be called priming.” What wasn’t known was how this happened.

What seems to be a temporary genetic change suggested that epigenetics was at work.  “An epigenetic change is one where there is a piece of information that is heritable through cell division, which is not encoded in changes in DNA sequence,” said Imperial College scientist Peter Sarkies.

Epigenetics is massively important, as it underlies the development of different tissues in the body. “The DNA sequence is not going to tell you very much about whether a cell is an eye cell or a liver cell,” Sarkies said.

But what both Sarkies and Guttierez-Marcos are studying is transgenerational epigenetics.  This is much harder to prove, but it lies behind the suggestions that the way humans live now can affect the biology of future generations.  An example where epigenetics is proposed is that of the Dutch Hunger Winter of 1944-1945, where it was claimed that not only were children born at this time smaller, but so were their children.

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In humans, the gametes are already established in the grandparents’ generation

Both scientists are using model organisms to test out their ideas. They grow quickly, and because many people work on them, there are lots of resources. The Warwick group used Arabidopsis, a fast-growing member of the mustard family, that only takes three months to grow, while Sarkies’ choice, C. elegans, a small threadworm, has a lifecycle of just three days.  This is the only realistic way of finding out how significant epigenetic communication between generations is.  Studying it in mammals is a researcher’s nightmare: “In plants the gametes are formed in the mother plant, but in humans, the gametes are already established in the grandparents’ generation,” said Gutierrez-Marcos.

Back to plants grown in poor conditions, and their seeds. Guttierez-Marcos has done some beautiful genetic experiments, and uncovered a novel genetic process, and I asked whether this also happens in crops. “It does, yes,” he said, “we have done it already. We have used maize.”

So can it be used practically?  He thinks so.  “We can prime crops one generation, two generations before they are grown in a particular environment; could be pathogens, could be drought, could be salinity.”

However, David Harris from the School of Environment, Natural Resources and Geography at Bangor University is more sceptical.  He has worked for years on a related phenomenon, seed priming, where seeds are pre-soaked in water, with and without added nutrients.  “It’s very very simple,” he said, “a major problem in smallholder farming in marginal areas of the tropics is that many times farmers sow their crops, and they don’t germinate very well, and we’ve been working on simple methods for improving that. And it usually entails a bucket of water and some careful timing.”

When I ask his opinion on whether the Warwick findings might have practical applications, he has two reservations.  The first is about the effect itself. “To be honest I would be quite surprised if there was much of an effect in that direction,” he said. “Most of our work suggests good quality seeds are a prerequisite for good quality growth, and any adaptation to poor conditions or good conditions or whatever, as a requirement is genotypic, not phenotypic.”

We will have to wait and see, but it seems to me that that is exactly where epigenetics fits in, blurring the boundary between the genetic make-up (the genotype) and what we see (the phenotype).

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Smallholder farming in Vietnam

His second concern is not about biology at all, and might be harder to resolve. “For me, the main problem with agricultural development in developing countries is the size of the farms, and the fact that they’re getting even smaller as they become subdivided over the generations. For most resource-poor smallholder farmers, it doesn’t really matter how much you increase the yield, a 50% increase of not very much is not very much. This has serious implications for their incentive for adopting improved practices and improved seeds.”

So whether or not priming of crops works, producing real change in society is a far more complex problem.  But the geneticists are helping us understand the natural world better, and presenting us with practical possibilities.  And with environmental uncertainty increasing, the more options we have, the better.

Neil Stoker is studying for an MSc in Science Communication

Images: Featured image: Crops, Tom (Flickr); Arabidopsis, Frost Museum (Flickr); Grandmother, Judysh (Pixabay);  Farming in Vietnam (Wikimedia Commons) 

Article: Wibowo, A., et al. 2016. Hyperosmotic stress memory in Arabidopsis is mediated by distinct epigenetically labile sites in the genome and is restricted in the male germline by DNA glycosylase activity. Elife, 5.

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