Nav: Home

Reducing the sweetness to survive

October 22, 2015

Plants produce a large arsenal of toxic compounds in order fend off herbivorous insects. To make sure that the toxicity of these defensive substances will not harm the plants themselves, many plants add a sugar molecule to some of their toxins. Digestive enzymes called glycosidases in the insect gut usually cleave off this sugar to release the toxin ? with harmful effects on the insects. Scientists at the Max Planck Institute for Chemical Ecology in Jena, Germany, now found the opposite mechanism: a defensive compound of the wild tobacco species Nicotiana attenuata which is toxic with sugar molecules bound to it and a glycosidase in the gut of the tobacco hornworm Manduca sexta which removes one sugar from this toxin to convert it to a non-toxic form. This is the first time that the role of deglycosylation in detoxification as an insect counter-adaptation could be shown (Nature Communications, October 2015).

Plants add sugars to their defensive compounds in order to avoid self-intoxication and to facilitate their transport and storage. The process of adding sugar to a chemical compound is called glycosylation. When herbivorous insects ingest these glycosylated toxins while feeding on plants, sugar-cleaving gut enzymes called glycosidases cleave these sugars from the defensive substances and the toxins are released in the midgut. The toxins can then exert deleterious effects on the insects' growth and fitness.

Scientists from the Max Planck Institute for Chemical Ecology examined defensive substances in the coyote tobacco Nicotiana attenuata. They were especially interested in a compound named lyciumoside IV which contains three sugar molecules and is toxic to larvae of the tobacco hornworm Manduca sexta. The ingestion of lyciumoside IV should usually cause severe body mass reduction in these caterpillars. It was thought that the sugar molecules were removed from lyciumoside IV in the Manduca sexta midgut and the released toxin caused these deleterious effects. However, what the researchers discovered contradicted the current understanding of the role of deglycosylation: lyciumoside IV is not completely deglycosylated, and what is more important, this compound itself and not its deglycosylated form is toxic. Glycosidases in the midgut of the tobacco hornworm larvae remove only one sugar molecule from lyciumoside IV which converts the toxin into a novel compound. Ingestion of this compound exerts no detrimental effects on the insects as those exerted by the ingestion of lyciumoside IV, suggesting that this novel compound is a detoxified form of lyciumoside IV. For the first time, scientists showed that removing a sugar molecule from a plant's defensive compound can also result in detoxification.

"That glucosidases which play an important role in digestion and toxin activation also function the opposite way and detoxify plant defensive substances, opens a new dimension of the plant-herbivore arms race. This discovery of an unusual detoxification mechanism can be mainly credited to our unbiased, reverse genetics-based 'ask the herbivore' and 'ask the ecosystem' approaches. The results obtained by using these approaches enabled us to find, understand and explain the mechanism which functions exactly contrary to the current understanding of glycosidases and detoxification mechanisms. Thus, this unbiased approach is one of our major contributions to the understanding of the complexity of plant defenses and insect adaptations," explains Sagar Pandit, one of the senior authors of the study.

The study revealed the significance of this unusual detoxification mechanism to the caterpillars in nature. The scientists first found the glycosidase responsible for removing the sugar from lyciumoside IV. Then they generated larvae with a suppressed glycosidase activity by silencing the respective larval glycosidase gene to study the effect of lyciumoside IV ingestion on the disabled larvae. The larval gene was silenced using a modern method called "plant-mediated RNA interference" in which transgenic tobacco plants were generated to produce the specific gene-silencing signal, which was transferred to larvae feeding on these plants. Interestingly, when the glycosidase-silenced larvae ingested lyciumoside IV, they failed to molt and eventually died. Glycosidase-silenced larvae which ingested the deglycosylated product did not show such molting failure and mortality. This suggested that the detoxification of lyciumoside IV is necessary to avoid these deleterious effects.

Many herbivores are known to store their host plant's toxic compounds in specialized compartments of their body, a process which is called sequestration. Usually, herbivores use sequestered compounds as their own defense against predators and parasites. The scientists therefore examined whether lyciumoside IV or its detoxified product protect Manduca sexta caterpillars against their natural enemies. Field experiments with glycosidase-silenced caterpillars revealed that the wolf spider Camptocosa parallela, a predator of tobacco hornworm larvae, captured and killed about the same number of glucosidase-silenced larvae and controls, but ingested significantly fewer glucosidase-silenced larvae. Larvae that had been coated with lyciumoside IV deterred the spiders; such deterrence was not observed when they were coated with the detoxification product. This clearly demonstrates that lyciumoside IV would have a protective effect if it was sequestered by the larvae. However, as the researchers showed, Manduca sexta larvae prefer to detoxify this plant defensive compound rather than sequestering it. The scientists infer that these larvae have not yet evolved the mechanism to co-opt lyciumocide IV and so they have to detoxify it in order to avoid the molting failure and mortality caused by its ingestion.

Now, the scientists want to find out whether there are natural Manduca sexta variants or related Manduca species that have already evolved a mechanism to co-opt lyciumoside IV and simultaneously avoid mortality and impairments. They are also interested in the question why the deglycosylation is restricted to the removal of only one sugar. By studying the responses to lyciumoside IV in Nicotiana attenuata's other specialist and generalist herbivores, they want to shed more light into this particular plant defense and the insects' counter-adaptations. [AO]
-end-
Original Publication:

Poreddy, S., Mitra, S., Schöttner, M., Chandran, J. N., Schneider, B., Baldwin, I. T., Kumar, P., Pandit, S. S. (2015). Detoxification of hostplant's chemical defense rather than its anti-predator co-option drives β-glucosidase-mediated lepidopteran counter-adaptation. Nature Communications, 6:8525, doi:10.1038/ncomms9525 http://dx.doi.org/10.1038/ncomms9525

Further Information:

Sagar S. Pandit, Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07743 Jena, Germany, +49 3641 57-1332, E-Mail spandit@ice.mpg.de

Ian T. Baldwin, Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07743 Jena, Germany, +49 3641 57-1101, E-Mail baldwin@ice.mpg.de

Contact and Media Requests:

Angela Overmeyer M.A., Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07743 Jena, +49 3641 57-2110, E-Mail overmeyer@ice.mpg.de

Download high-resolution images via http://www.ice.mpg.de/ext/downloads2015.html

Max Planck Institute for Chemical Ecology

Related Insects Articles:

A robot to track and film flying insects
French scientists have developed the first cable-driven robot that can follow and interact with free-flying insects.
Dramatic loss of food plants for insects
Just a few weeks ago, everyone was talking about plummeting insect numbers.
The brains of shrimps and insects are more alike than we thought
Crustaceans share a brain structure known to be crucial for learning and memory in insects, a University of Arizona-led research team discovered.
Freshwater insects recover while spiders decline in UK
Many insects, mosses and lichens in the UK are bucking the trend of biodiversity loss, according to a comprehensive analysis of over 5,000 species led by UCL and the UK Centre for Ecology & Hydrology (UKCEH), and published in Nature Ecology & Evolution.
Hundreds of novel viruses discovered in insects
New viruses which cause diseases often come from animals. Well-known examples of this are the Zika virus transmitted by mosquitoes, bird flu viruses, as well as the MERS virus which is associated with camels.
Tiny insects become 'visible' to bats when they swarm
Small insects that would normally be undetectable to bats using echolocation suddenly become detectable when they occur in large swarms.
Helpful insects and landscape changes
We might not notice them, but the crops farmers grow are protected by scores of tiny invertebrate bodyguards.
New information on tropical parasitoid insects revealed
The diversity and ecology of African parasitoid wasps was studied for over a year during a project run by the Biodiversity Unit of the University of Turku in Finland.
Insects need empathy
In February, environmentalists in Germany collected 1.75 million signatures for a 'save the bees law.' Citizens can stop insect declines by halting habitat loss and fragmentation, producing food without pesticides and limiting climate change, say the authors of this Perspectives piece in Science.
Migratory hoverflies 'key' as many insects decline
Migratory hoverflies are 'key' to pollination and controlling crop pests amid the decline of many other insect species, new research shows.
More Insects News and Insects Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.