Canny breeding creates vitamin A-rich maize without genetic modification

Blogging on Peer-Reviewed ResearchOn Thursday, I wrote about a way of genetically modifying carrots to turn them into rich sources of calcium. The method could be more widely used in vegetables to help reduce nutritional deficiencies, but it risks raising the ire of the anti-GM environmentalist camp. But there is another way of altering the genes of crop plants that avoids such controversy, and it’s a traditional one – selective breeding.

Types of maizeBy cross-breeding individuals with desirable qualities, farmers have been tinkering with the genes of both animals and plants for centuries. Traditionally, the process has been a bit messy. Genes don’t always easily translate into physical characteristics, so there is a certain amount of trial-and-error involved.

Now, Carlos Harjes from Cornell University had developed a way of using modern genetic techniques to make selective breeding even more selective. For his first trick, he has developed a variety of maize to combat vitamin A deficiencies. Best of all, no genes were added, tweaked or subtracted in the making of this vegetable – he only used the natural genetic variation within the world’s maize strains.

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Meet the genetically modified super-carrot, now fortified with calcium

Blogging on Peer-Reviewed ResearchFor centuries, mothers have wrongly told their children that eating carrots will improve their vision. The sight-enhancing properties of these iconic vegetables is be a myth (albeit a fascinating one involving Nazis and fighter pilots) but if Jay Morris has anything to say about it, they may soon be better known for building strong bones.

Types of carrotsMorris, together with Kendal Hirschi and other Texan colleagues, has found a way to double the calcium content of carrots through genetic modification, making them a rich source of the element that is so vital for bones

The team loaded their super-carrots with a protein called sCAX1, which pumps calcium into the plant’s cells. The protein originally hailed from the plant-of-choice for geneticists, Arabidopsis thaliana, where it exists in a larger version. Morris’s team lopped off a small piece from its tip that stops the protein from funnelling in more calcium once a certain amount has been reached.

In this shortened form, sCAX1 is relentless in its import of calcium and the researchers have found that it can greatly increase the calcium content of several vegetables including tomatoes, potatoes and carrots. These super-charged vegetables could help to reduce the risk of osteoporosis, one of the world’s leading nutritional disorders, where a lack of calcium leads to brittle bones.

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The effect of GM crops on local insect life

A large study weighs up the existing evidence on the impact of GM crops on local insect life, providing some much-needed scientific rigour to the GM debate.

In Europe, the ‘GM debate‘ about the merits and dangers of genetically-modified (GM) crops is a particularly heated one. There is a sense of unease about the power of modern genetic technology, and a gut feeling that scientists are ‘playing God’. These discontents are stoked by the anti-GM camp, who describe GM crops with laden and fear-mongering bits of unspeak like ‘Frankenstein foods’ and ‘unnatural’.

Bt cotton is better for non-targeted insects than non-resistant crops sprayed with insecticdes.In a debate so fuelled by emotion and personal values, scientific research and a critical analysis of the evidence rarely gets a look-in. But science has to grudgingly admit some blame in this, because there is actually precious little research on the safety of GM crops. And many of the studies that have been done were short-term and poorly replicated.

A lack of research is dangerous. It provides opening for people on either side of the debate to quote single, small studies as canon and brushing aside any research that contrasts with their stances.

Adding evidence to the debate

Michelle Marvier and colleagues from Santa Clara University, California, are trying to change all that. They have analysed over 42 field experiments on GM crops to get an overall picture about their safety. The technique they used is called meta-analysis, a statistical tool that asks “What does everyone think?” It works on the basis that individual small studies may be far from conclusive, but pooling their results together can lead to stronger and more accurate results.

They looked at three strains of GM-crops that had been modified with genes from a soil-dwelling bacterium called Bacillus thuringiensis. The transferred genes are responsible for producing a number of biological (and therefore ‘natural’) insecticides. When moving them across to plants, geneticists typically try to match the insecticide to the pest they are trying to fight. (In the image on the right, Bt-peanut leaves are protected from the damaging European corn borer)Some GM crops are resistant to specific insect pests.

The toxins are delivered at high dosages to pests, but are restricted to the plant (and sometimes even to particular tissues). They can also be added to the chloroplast genome, which is quite separate form the plant’s nuclear DNA. This stops them from being transferred to other plants.

The hope is that these so-called ‘Bt crops’ can help to minimise the collateral damage of less targeted insecticide sprays. In theory, only pest insects that eat valued crops are killed, while the rest of the ecosystem is unharmed.

The results

That’s what Marvier set out to test. She looked at field experiments which tested the impact of caterpillar-resistant cotton and maize plants on the abundance of other groups of insects and invertebrates.

She found that these other creatures are found in greater numbers in fields containing the caterpillar-resistant GM plants, compared to those sprayed with conventional insecticides. However, the GM crops also led to slightly lower numbers of non-targeted insects compared to fields where no GM crops and no insecticides were used.

The results stayed the same even when Marvier analysed them in more detail. For example, she found much the same thing when she only looked at experiments that had been published in peer-reviewed scientific journals.

So assuming that Bt crops do indeed reduce the use of insecticides (and that’s far from proven), then they will also, as claimed, reduce the collateral damage caused by these chemicals. But they’re not as good for the environment as using no insecticides at all, be they engineered or sprayed.

The bigger picture

Bt-crops are better than large-scale insecticide spraying.At the local level, Marvier’s study provides some much-needed scientific backbone to the GM debate. But the real decisions need to be weighed up at a larger level. For example, it’s all well and good to say that a no-insecticide, no-GM field is the best solution, but that leaves farmers in a bit of a lurch.

One of the big criticism levelled against organic farming is that it leads to lower yield than other practices and requires more agricultural land to be viable and that deals a bad hand to farmers in the developing world. This in turn could lead to deforestation and habitat loss.

On the other hand, Marvier advises caution when interpreting her work. This study has revealed just one benefit of GM crops and even then, only for one specific type of genetic modification. Many of the studies involved isolated patches of land, rather than entire farming systems, where the situation is more subtle. Not all non-GM crops are sprayed with insecticides, while not all GM crops are free from them.

Any benefits must also be weighed against potential health or environmental risks, and again, these must be researched carefully.

To Marvier, the clearest message from her study is that we have started to accumulate enough data to look at this issue from an empirical, evidence-based point of view. If we are to make sound decisions, there is little room for anecdotal evidence or knee-jerk responses guided by personal philosophy.

Bt hypocrisy

For example, there is a certain irony to the opposition to Bt crops. Because its insecticides are ‘natural’, the bacterium is one of the few pesticides that organic farmers are allowed to spray onto their crops.

The bacteria of course use the exact same genes that are transplanted into Bt-engineered crops. Some may argue that this method is better because it is more ‘natural’, because the genes stay within the organism they were intended for. But is that really better?

Wholesale Bt spraying is a crude technique than the specific and targeted use of Bt-engineered crops. It means that the surrounding land is also covered in the bacteria and creatures other than pests are exposed to its entire gamut of toxins. And because farmers need constant supplies of the bacteria, it soaks up more money.

Reference: Marvier, McCreedy, Regetz & Kareiva. 2007. A meta-analysis of effects of Bt cotton and maize on nontarget invertebrates. Science 316: 1475-1477.

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Related stories on genetic modification:

Genetically-modified mosquitoes fight malaria by outcompeting normal ones
Magnifection: mass-producing drugs in record time
Feed the world – turning cotton into a food crop

Genetically-modified mosquitoes fight malaria by outcompeting normal ones

Genetically-engineered mosquitoes that are resistant to the malarial parasite could be the key to reducing the burden of malaria. In laboratory experiments, they are stronger and fitter than their normal peers and rapidly dominate the population.

Fighting malaria with mosquitoes seems like an bizarrely ironic strategy. But that’s exactly what many scientists are trying to do.

The Anopheles mosquito carries the malaria parasite Plasmodium, but at a cost to its own health.Malaria kills one to three million people every year, most of whom are children. Many strategies for controlling it naturally focus on ways of killing the mosquitoes that spread it, stopping them from biting humans, or getting rid of their breeding grounds.

But the mosquitoes themselves are not the real problem. They are merely carriers for the true cause of malaria – a parasite called Plasmodium. It suits neither mosquitoes nor humans to be infected with Plasmodium, and by helping them resist it, we may inadvertently help ourselves.

With the power of modern genetics and molecular biology, scientists have produced strains of genetically engineered mosquitoes that cannot transmit the malarial parasite.

These ‘GM-mosquitoes’ carry a modified gene – a transgene – that produces chemicals which interfere with Plasmodium’s development. Rather than becoming suitable carriers, the modified mosquitoes are death for any invading Plasmodium.

But scientists can’t very well change the genes of every mosquito in the tropics. To actually reduce the burden of malaria, the genetic changes that induce malaria resistance need to be spread throughout the mosquito population. The easiest way to do this is, of course, to let the insects do it themselves.

And Mauro Marrelli and colleagues from the Johns Hopkins University have found that they are more than up to the task.

The Plasmodium parasite causes malaria but can’t survive in genetically modified mosquitoes.They kept cages full of equal numbers of engineered and normal mosquitoes and fed them on the blood of mice infected by Plasmodium. After nine generations, they found that the engineered insects had become proportionally more common, making up about 70% of the total population.

Like most parasites, Plasmodium affects the health of its host. So mosquitoes that are parasite-resistant are stronger and fitter than their infected peers. Marrelli found that they were about 25% less likely to die early, and had more young, with every female laying an average of 60 eggs compared to 43.

With these advantages, the transgenic mosquitoes outlasted and out-bred normal ones, and quickly established a majority in the population.

But if the advantages to resistance are so great, why haven’t naturally-resistant mosquitoes replaced non-resistant ones? Other studies have shown that resistant mosquitoes fight off Plasmodium with the help of hyperactive immune systems, but have no evolutionary advantages over carriers.

Marrelli thinks that because chronic immune responses produce health problems of their own, that cancel out the advantage of not carrying Plasmodium. In contrast, the transgenic mosquitoes are simply expressing a gene that is mostly harmless. The gene also kills Plasmodium early on in its life cycle, well before it triggers the body’s own immune system.

Even though a single transgene copy does not affect the modified insects’ health, it appears that two copies might have some as-yet-unknown health consequences. This may explain why the resistant mosquitoes in Marrelli’s experiments did not totally dominate the population, but plateaued at 70%. The strongest mosquitoes are those with just one copy of the gene.

Malaria affects tropical countries around the world.This means that introducing the engineered mosquitoes into the wild would not completely wipe out their disease-spreading cousins. But it would still drastically cut their numbers. Considering that malaria infects over 400 million people a year, reducing this number by 70% would be a monumental victory for international health.

Nonetheless, Marrelli is cautious about the future of malaria-resistant strains. These experiments are a proof-of-principle and their results may not bear out as planned in practice.

In the field, only a relatively small proportion of mosquitoes become infected, and he expects the spread of the transgene to be slower. But if it becomes established, it could complement other programmes for controlling malaria, by making it very hard for the parasite to re-colonise a cleared area after it has been eradicated.


Reference: Marrelli, Li, Rasgon & Jacobs-Lorena. 2007. Transgenic malaria-resistant mosquitoes have a fitness advantage when feeding on Plasmodium-infected blood. PNAS 104: 5580-5583.

Images: Plasmodium image by Ute Frevert

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Feed the world – turning cotton into a food crop

The world’s cottonseed harvest have enough protein to feed half a billion people in the world’s poorest places, but are inedible because they contain a potent poison. Now, scientists have found a way of removing that poison, and turning cotton into a stunning new food source.


Feed the world. Let them know it’s Christmas time.” The world is currently home to 6.5 billion people and over the next 50 years, this number is set to grow by 50%. With this massive planetary overcrowding, Band Aid’s plea to feed the world seems increasingly unlikely.

Current food crops seem unequal to the task, but scientists at Texas University may have developed a solution, a secret ace up our sleeves – cotton.

Cotton is infused with a potent poison called gossypol. Cotton is famed for its use in clothes-making and has been grown for this purpose for over seven millennia. We do not think of it as a potential source of food, and for good reason.

The seeds of the cotton plant are rife with a potent poison called gossypol (see below) that attacks both the heart and liver. Only the multi-chambered stomachs of cattle and other hooved animals can cope with this poison, relegating cottonseed to a role as animal feed.

Getting rid of gossypol could go a long way to reducing the world’s hunger crisis. A fifth of a cottonseed’s weight is made up of oil, and a quarter of high-quality protein. For every kilogram of fibre, each cotton plant produces 1.65 kg of seed.

And the plant is grown in over 80 countries by some 20 million farmers, the majority of whom live in the poorest parts of the world, where starvation is an ever-looming threat. If only the seeds could be made edible.

GossypolIn 1954, scientists attempted to launched a programme to cross-breed normal cotton plants with a mutant strain that lacked the glands that make gossypol. Unfortunately, they discovered that cotton creates the poison for a reason.

It infuses the plant’s various tissues, protecting it from insect pests and infections alike. The programme’s seeds were safe for human consumption, but the weakened plants readily succumbed to insect attacks, destroying their commercial potential.

Now, Ganesan Sunilkumar and colleagues have solved the problem. They have used a technique called RNA interference, or RNAi, to turn off a gene called delta-cadinene synthase, which is essential for gossypol production.

But in this case, the team put their system under the control of a genetic switch used only in cotton seeds, and not the rest of the plant. As a result, levels of gossypol plummeted in the plant’s seeds and these alone. The rest remained as strong as ever against attackers.

Sunilkumar ran their special plants through a series of tests to make sure that the RNAi’s effects never spread to the rest of the plant. They passed every one. Best of all, the altered plants stably passed on their characteristics to their daughters.

This study is testament to both the power and the precision of modern genetic technology. The researchers identified a very specific point in a biochemical pathway and blocked it in a single part of the plant. The result is a variant that retains the original’s survival abilities, but is suddenly fit for human consumption.

Their approach has tremendous potential for opening up other food sources. For example, the beans of the tropical grass pea, Lathyrus sativus, are often eating by poor people in Africa and Asia in times of dire need.

As the beans contain a potent neurotoxin – a nerve poison – those eating them often contract a neurological disease called lathyrism. With Sunilkumar’s technique, lathyrism could become a thing of the past.

For those who feel that the use of such technology is tantamount to playing God, consider this. Every year, 44 million tons of cottonseed are wasted. With this new technology, the engineered seed could provide enough protein for half a billion people every year.

Sunilkumar, Campbell, Puckhaber, Stipanovic & Rathore. 2006. PNAS 103: 18054-18059.

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