The knowledge base that has been generated by plant scientists since the first plant genome was sequenced 12 years ago is huge. Plant biotechnology has such a lot to offer. This is a beautiful example of putting that knowledge into practice.
Professor Barbara Ann Halkier
Plant biologists at the University of Copenhagen, Denmark, have developed a method to limit the presence of toxins in oilseed rape with the potential to make by-products of rapeseed oil production more suitable for use as protein-rich animal fodder.
Rapeseed, also known as oilseed rape or simply rape, is the third most widely grown oilseed-producing crop in the world (other oilseed crops include sunflowers, mustard and castor). Rapeseed contains types of glucosides known as glucosinolates, which have been shown to have adverse effects when used as the main feedstuff of non-ruminants.
Published this week in the journal Nature
, the paper represents the culmination of 16 years of basic research aimed at understanding how these glucosides are transported into the seeds of rape plants. While the researchers originally believed it might be possible to reduce the amount of glucosides present in the seeds by ten or perhaps 20 per cent, their innovative approach in fact enables a 100 per cent reduction and presents the hope that more rapeseed meal could be produced and used in northern Europe.
Professor Barbara Ann Halkier from the University’s Faculty of Science is head of the Center of Excellence for Dynamic Molecular Interactions (DynaMo), which was established in January this year. I spoke to her to find out more about the possibilities for ‘transport engineering’…What makes glucosinolates toxic? Why is that some are not only non-toxic but healthy?
Typically, more than 30 different glucosinolates are produced by the various members of the cabbage family, or Brassicaceae
. Cress doesn’t taste the same as radishes, and radishes don’t taste the same as broccoli or cauliflower or Brussels sprouts – they each taste different because they have a slightly different composition. One of the reasons broccoli has received so much attention recently is that it contains high concentrations of a certain type of glucoside which has been associated with cancer prevention.
Rape cake – the solid that is left after you’ve pressed the oil from the seed of oilseed rape, Brassica napus
– contains a particular glucoside which inhibits growth in pigs in poultry. Ruminants such as cows have more than one stomach so they can deal with it, but one-stomached animals are affected. For that reason there is a limit to how much rape cake you can use as fodder for pigs and poultry. That is why at our latitude we import a lot of soy cake to supply enough protein for the meat we want to produce. What is innovative about the technology you and your colleagues have developed?
Our technology enables us to remove the toxic compound from those parts of the crop meant for fodder. We studied a model plant called thale cress, or Arabidopsis thaliana
. We prevent the accumulation of glucosides by blocking the import of the toxic compound into the seed. This is why we call it ‘transport engineering’; because a transport pathway is blocked.
Normally you would try to inhibit synthesis, but here we kept synthesis going as usual. Hence the plant’s leaves have the defence compounds they need to protect it, but we are blocking the movement of these compounds into the seeds of the next generation. This is not a problem because we’re not harvesting these seeds to sow them again. The technique used means that the generation produced have no glucosides in their seeds, but come from a father and mother that do.
That’s how we found these transporters. We found them by screening a library of transporters in oocytes (eggs) from frogs, identifying them by looking at mutants that were mutated in exactly that transporter and its closest homologue. When we crossed the two mutants together we got a plant with no glucosides in the seeds. The great thing is that the defence compounds are kept in the rest of the plant, meaning that it maintains the ability to defend itself. They actually have higher levels of these defence compounds because the glucosides that would go into the seeds remain in the green parts of the plant. This might mean that fewer pesticides are needed also. Why was thale cress used in your experiments?
Thale cress is the
model plant. It was the first plant to have its genome sequenced, in 2000, and the reason it was chosen is because it’s the plant equivalent of yeast. It has a very short life cycle at only eight weeks, is easy to transfer and has a very small genome. The plant science community has been able to generate many tools from it; molecular tools are more widely available for this plant than any other.
We had the advantage, in our study of glucosides, that these compounds are found in thale cress and therefore we were able to carry out our proof of concept in that system. We are also fortunate that rape is very closely related to thale cress. The biotech company Bayer CropScience immediately saw the potential of our technology from the proof of concept study and have initiated collaboration with the University of Copenhagen to translate this technology into rape.Are there other potential uses for the transport engineering methods you have developed?
Yes. For example, in the tropical potato or cassava, which is very drought resistant and is eaten widely throughout Africa, another toxin – a cyanogenic defence compound – is transferred from the leaves down into the tuber. We can imagine that transport engineering could be applied to block the transport pathways and produce tubers without the cyanogenic glucosides. What are the potential benefits and risks of the introduction of this technology?
The amount of rape cake that pigs and poultry can be fed is limited, so we supplement it by importing a lot of soya. We imagine that the commercial potential of rape as an animal feed crop could be increased using this technology. For us in northern Europe where we grow a lot of rape and not much soya, it would mean we could be much more sustainable and grow more locally. In that sense we think it has a lot of potential.
Another aspect of this technique’s potential within the rape breeding field relates to selection for increased yield; a lot of the new lines generated have to be discarded because they have high glucoside levels. Consequently, the biodiversity within the pool of rape cultivars used for breeding is currently very small. Our technology enables the use of ancient cultivars which may produce higher yields. They may also display higher glucoside content in the green parts of the plant, but it is not a problem, because transport into the seeds is blocked.
The technology used to translate this into rape could be either GM technology, where we eliminate insertions of particular mutants, or non-GM technology. Personally speaking, I’m not particularly afraid of GM technology, and I think this goes to show that we should not be so afraid of using it if it is possible to make such great breakthroughs. The knowledge base that has been generated by plant scientists since the first plant genome was sequenced 12 years ago is huge. Plant biotechnology has such a lot to offer. This is a beautiful example of putting that knowledge into practice.