There is currently a lot of excitement regarding the field of epigenetics and the production of Australian wine.
It's a relatively new research area in molecular biology and as such it's often misunderstood. There's even still some controversy about just how significant it is, but it is a field that is full of promise and looks to be highly relevant to viticulture.
Put simply, many scientists think that epigenetics could be a way that vines 'remember' environmental stresses and that by applying insights from epigenetics it might be possible to adapt vines to difficult conditions they might later be exposed to. Experiments are ongoing and early results are positive.
What exactly is epigenetics?
It sounds like science fiction and it's fiendishly complex to explain in a straightforward way, so it's probably best to begin with some basic genetics. In each of our cells we have a full set of genes – around 19 000 of them in the human genome and 30 000 in the grapevine’s – in two interlocking strands of deoxyribonucleic acid (DNA). There are equal contributions from our mother and our father. This is the DNA library that makes us 'us', and the key factor is how these genes are then read by each cell. Each gene codes for a protein, but in each cell only a subset of these genes is 'expressed' (the term for a gene being switched on, so that it then produces a protein). The pattern of gene expression determines the identity and also the ongoing functioning of each cell. This is how cells differentiate into the many different types we have in our bodies: skin, nerve, blood, bone and so on.
"Think of them as molecular dimmer switches: they are mechanisms for turning genes on or off, or turning them up or down."
Most of us are familiar with the notion of evolution: that mutations occur in our cells whereby there are changes in the DNA sequence and when these changes occur in sex cells (producing sperm and eggs), they can be passed on. Most of the time these mutations are bad, but sometimes they can be good. Over many generations there is selection for organisms who have the most reproductive success and genes that contribute to this success will be selected and increase in frequency. But it turns out that there are some heritable changes that can be passed on without any changes to the genetic code itself, a notion that seems slightly heretical for those schooled on Darwinian evolution. This is epigenetics.
Epigenetics refers to heritable change in the way that DNA is read, even though the DNA stays the same. Epigenetics transmits information separately from DNA changes by mechanisms such as DNA methylation (the most well-studied), histone modifications, chromatin remodelling and non-coding ribonucleic acid (RNA) changes. These chemical alterations change the way that the DNA is packed, or act as barriers to stop certain bits being read. Think of them as molecular dimmer switches: they are mechanisms for turning genes on or off, or turning them up or down. The exciting thing is that these changes can be passed on to daughter cells when cells divide and can even be passed transgenerationally, from parents to their offspring. This is what makes epigenetics so interesting, because it is dealing with heritable changes without changing the DNA sequence itself.
Epigenetics is particularly exciting for wine production. When new plants are generated from cuttings, genetically identical clones of the same plant are produced. But it was noticed a long time ago that even though propagated plants have the same DNA sequence – they are clones – they often grow differently, a phenomenon described as somaclonal variation. One of the causes of this variation turns out to be epigenetics, caused by exposure to different environments. Plant scientists were interested in seeing whether exposing the plant tissue to various stresses could result in epigenetic changes that caused the plant to adapt to these stresses, and then remember this adaptation when the clone was propagated for planting in the field.
Rachel Steer – Modern Australian Viticulturist
This is really interesting for viticulture because vines are often exposed to hostile environments and stay put for 20 or more years. Could vines be adapting to their environment? Can these adaptations be captured in cuttings?
A research project currently underway at The University of Adelaide that has built on research in other plants that propagate via seeds. This research showed that it is possible to prime plants for stresses such as low relative humidity, heat, high salt levels or disease, and that this epigenetic priming can be passed on to the next generation, making the new plants more tolerant to these stresses.
Old vine characteristics from young vines?
Vines do have sex, but each time they do a new variety is produced and very few of these new varieties are as good as their parents from a winemaking point of view. It's for this reason that vines are reproduced from cuttings, keeping the variety’s characteristics. Sometimes, certain vines in a vineyard seem to perform better than others and so cuttings might be taken and specifically propagated to maintain this beneficial trait. This is how clones are produced.
So, are epigenetic changes also relevant here? University of Adelaide researchers Dr. Carlos Rodriguez Lopez and Dr. Roberta De Bei in collaboration with Dr. Everard Edwards from CSIRO looked at whether vines can 'remember' being exposed to heat and drought through epigenetics and specifically, they examined DNA methylation patterns. Their pilot study showed proof of concept: some of the epigenetic markers of stress persisted for a month after the stress was removed.
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Initially, these epigenetic changes could be used to produce cuttings that are more tolerant to water and heat stress. This would reduce the cost of establishing a new vineyard and also lower the environmental impact of this process. Beyond this though, there are more implications of epigenetic changes in vines. Might it be possible to study vines in an old vineyard and select cuttings that have epigenetic changes that have helped adapt the vine to the place? If those changes would persist in the next generation of vines, then this could help produce vines that are better adapted to certain environments. It may then be possible to get some of the benefits of old vines with younger vineyards. One of the other advantages of epigenetic research is that it doesn’t involve genetic modification.
As is usual, more research is required and this is underway. After the success of the pilot trial, a new two-year study will analyse to what extent the epigenetic memory of drought and heat stress is maintained four years after discontinuation of the initially experienced stress. The cuttings of Cabernet Sauvignon that were exposed to stress in the first project will be exposed again to the same stresses and researchers will track the epigenetic modifications and also the way the vines respond to these stresses. These plants will be propagated vegetatively using both dormant and green cuttings and the old-fashioned technique of layering, to see how durable the epigenetic changes are.
This is just the beginning of understanding the role of epigenetics in viticulture and it's going to be a field that's worth following over the next few years.
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