Nav: Home

The chemical language of plants depends on context

July 01, 2019

A team of scientists from the Max Planck Institute for Chemical Ecology in Jena, Germany, studied the ecological function of linalool, a naturally abundant volatile organic compound, in wild Nicotiana attenuata tobacco plants. They found the gene responsible for linalool synthesis and release which vary considerably in plants of the same species. Females of the tobacco hawkmoth (Manduca sexta) prefer to lay eggs on plants with a higher naturally occurring linalool. At the same time, the more linalool a plant released, the more eggs and freshly hatched larvae were predated on by bugs. Behavioral assays in increasingly complex environments showed that the effects of linalool are quite variable, depending on the natural environment and the genetic makeup of the plant (Proceedings of the National Academy of Sciences of the United States of America, DOI: 10.1073/pnas.1818585116).

Interactions between tobacco plants, tobacco hawkmoths, and predatory bugs

Plants have evolved multiple strategies to defend themselves against herbivorous animals, especially insects. In addition to mechanical defenses, such as thorns and spines, plants also produce chemical defense compounds that hold insects and other herbivores at bay. These substances include volatile organic compounds, often only produced by plants after insect attack. Linalool is such a plant volatile organic compound; it mediates different ecological interactions with insects. Its complex mode of action has already been the subject of previous investigations. It is known that linalool in tobacco plants can attract predatory Geocoris bugs to show them the way to their prey: the eggs or freshly hatched larvae of tobacco hawkmoths. However, as a floral scent component, linalool is also attractive for adult hawkmoths and influences mated female moths in their decision to lay their eggs on a plant. A team of scientists from the Max Planck Institute for Chemical Ecology lead by Meredith Schuman and Ian Baldwin has now studied the ecological functions of the monoterpene linalool in wild Nicotiana attenuata plants in more detail.

The genetic analysis of linalool synthesis

The researchers observed a correlation between the rate of Manduca sexta eggs predated by Geocoris bugs and the amount of linalool produced by the respective plants. They didn't observe such a correlation between five similar organic compounds emitted by tobacco plants and the egg predation rate. This indicates that linalool, in fact, functions as the plants' chemical cry for help and attracts predatory bugs that attack herbivorous larvae. "Tobacco plants vary a lot in their linalool emission. If linalool mainly has a defensive effect, that is attracting predators and repelling hawkmoths, we would expect there to be less variation. Obviously, linalool emission is not always advantageous for the plant. Therefore we wanted to explore systematically, which ecological interactions result from differences in linalool production," Jun He, the first author of the study, explains.

The scientists were able to identify the enzyme that regulates linalool synthesis in Nicotiana attenuata and to determine its genetic basis. To achieve this, they crossed plants from native populations in Arizona which were high in linalool production, with plants from Utah which produced considerably less linalool. This approach, which is called forward genetics, allowed for an identification of genes underlying the natural variation of linalool synthesis.

Mirror images of molecules and their different effects

Linalool occurs in two different forms, so called enantiomers. Both enantiomers, (R)-(?)-linalool and (S)-(+)-linalool, are almost identical, however, their three-dimensional structures are mirror images of each other. Although only (S)-(+)-linalool was found in natural Nicotiana attenuata populations in Utah and Arizona, the researchers also used plants in their experiments which produced its mirror image, (R)-(?)-linalool. Both enantiomers are perceived as two different compounds by hawkmoths, resulting in different effects on their behavior.

Experiments in an increasingly complex context

The scientists tested the effect of these plants in behavioral assays with tobacco hawkmoths. They observed the behavior of mated females exposed to two different experimental plants in a choice assay in a wind tunnel in order to answer the question how linalool blends affect oviposition. Amazingly, egg-laying was only partially influenced by a manipulated production of the two linalool enantiomers. In fact, the genetic background of the plants, that is, whether a Utah or an Arizona plant had been modified to produce more linalool, had a much higher impact on the moths' preferences. "It was surprising to us that experimental context mattered even more than the two different enantiomers", Richard Fandino, who designed the wind tunnel experiments, explains. The researchers performed further experiments with moths and different tobacco plants in oviposition chambers and a large experimental tent, where moths were able to fly around. However, the differences in the moths' responses to linalool emission vanished, the more complex the environment became.

The meaning of signals in context

Context is a linguistic term. It points to the problem that words or vocabulary may have different meanings depending on the communication situation in which they are used. This is also true for the "chemical vocabulary" component, linalool. Originally, the authors of the study expected that a chemical compound triggers a certain behavior. "However, our study showed that moths pay attention to many different features of plants when choosing where to feed or oviposit. Then, they integrate this information in order to choose among the available plants. Thus, differences in other plant properties as well as the availability of alternative plants and their characteristics, are likely to determine the importance of any individual cue: in this case, linalool", Meredith Schuman, one of the main authors of the publication, summarizes.

A better understanding of context-appropriate plant defense against herbivores might help to overcome problems in standardized industrial agriculture, such as the evolution of resistance to commonly used pesticides.
-end-
Original Publication:

He, J., Fandino, R. A., Halitschke, R., Luck, K., Köllner, T. G., Murdock, M. H., Ray, R., Gase, K., Knaden, M., Baldwin, I. T., Schuman, M. (2019). An unbiased approach elucidates variation in (S)-(+)-linalool, a context-specific mediator of a tri-trophic interaction in wild tobacco. Proceedings of the National Academy of Sciences of the United States of America, DOI:

10.1073/pnas.1818585116

https://doi.org/10.1073/pnas.1818585116

Further Information:

Ian T. Baldwin, Max Planck Institute for Chemical Ecology, Hans-Knöll-Straße 8, 07745 Jena, Germany, +49 (0)3641 57 1100, baldwin@ice.mpg.de

Meredith C. Schuman, University of Zurich, Department of Geography, Winterthurerstrasse 190, 8057 Zürich, Switzerland, +41 44 63 55162, meredith.schuman@geo.uzh.ch

Contact and Media Requests:

Angela Overmeyer M.A., Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07745 Jena, +49 3641 57-2110, E-Mail overmeyer@ice.mpg.de

Max Planck Institute for Chemical Ecology

Related Moths Articles:

Deaf moths evolved noise-cancelling scales to evade prey
Some species of deaf moths can absorb as much as 85 per cent of the incoming sound energy from predatory bats -- who use echolocation to detect them.
Moths' flight data helps drones navigate complex environments
The flight navigation strategy of moths can be used to develop programs that help drones to navigate unfamiliar environments, report Ioannis Paschalidis at Boston University, Thomas Daniel at University of Washington, and colleagues, in the open-access journal PLOS Computational Biology.
Moths and perhaps other animals rely on precise timing of neural spikes
By capturing and analyzing nearly all of the brain signals sent to the wing muscles of hawk moths (Manduca sexta), researchers have shown that precise timing within rapid sequences of neural signal spikes is essential to controlling the flight muscles necessary for the moths to eat.
Lazy moths taste disgusting
Researchers have noticed that some moths are nonchalant when attacked by predatory bats.
Research explores how grape pests sniff out berries
A new study, published Nov. 21 in the Journal of Chemical Ecology, investigates how these pests find their target amid a sea of other plants in the landscape.
New to science New Zealand moths link mythological deities to James Cameron's films
In an unexpected discovery, two species of macro-moths were described as new species endemic to the South Island, New Zealand.
Four new species of plume moths discovered in Bahamas
Deborah Matthews hunts for plume moths in darkness, waiting for the halo of her headlamp to catch a brief flicker.
Russian scientists make discovery that can help remove gypsy moths from forests
The caterpillars of Lymantria dispar or Gypsy Moth are voracious eaters capable of defoliating entire forests.
Deaf moth evolves sound-production as a warning to outwit its predator
A genus of deaf moth has evolved to develop an extraordinary sound-producing structure in its wings to evade its primary predator the bat.
Antennal sensors allow hawkmoths to make quick moves
All insects use vision to control their position in the air when they fly, but they also integrate information from other senses.
More Moths News and Moths 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: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.