Terpenes (general)

The Hiring of Bodyguards by Plants Through the Release of Terpenes

Throughout nature, terpenes tempt us with their scents, pulling us closer to a flower or hop cone or cannabis bud for a deeper inhalation to better entwine the emitted aromas with our senses. Terpenes are more than just fragrances or flavors, and it’s been well publicized that the many terpenes throughout our world bestow a bounty of therapeutic possibilities. But there is so much more to the roles of terpenes.

One of the most fascinating attributes of terpenes is their ability to help plants communicate with the animal world, specifically with insects. A plant, when under attack from an herbivorous insect, may release terpenes that taste bitter to discourage its destruction. Or, plants may emit terpenes into the atmosphere with the hopes that some hungry, carnivorous insect intercepts the cry for help, and comes to the plant’s rescue.

This phenomenon was demonstrated by researchers using the model plant Arabidopsis thaliana. [1] The first step the researchers undertook was to get A. thaliana to create the volatile constituents they sought to study, and they achieved this via engineering transgenic plants. The terpenoid they chose to exploit in the plants was (3S)-(E)-nerolidol (trans-nerolidol), which is common to important agricultural crops like tomatoes and corn.

(3S)-(E)-Nerolidol also happens to be an intermediate molecule during the biosynthesis of 4,8-dimethyl-1,3(E),7-nonatriene ((E)-DMNT), an inelegantly named acyclic monoterpenoid that makes up part of the volatile emissions native to A. thaliana.

The researchers built upon previous research that sought to produce larger quantities of sesquiterpenes, but that failed due to “a lack of sufficient precursors.” The past experiments targeted the cytosol, where the precursor of sesquiterpenes called farnesyl diphosphate (FPP) is located, or in the plastids. The authors of the study decided to target an enzyme (strawberry linalool/nerolidol synthase) in the mitochondria, hypothesizing that FPP would also be present there.

This approach led to a 20-30x increase in (3S)-(E)-nerolidol compared to where plastids were targeted. The terpenoid was not detected in wild-type plants. Five of the nine transgenic plants also showed (E)-DMNT which had never been detected before in Arabidopsis foliage after it had been fed upon by insects or in the wild-type plants.

Interestingly, mastication by spider mites or caterpillars did not provoke emission of (3S)-(E)-nerolidol or (E)-DMNT in wild-type Arabidopsis despite their inducing these molecules in other plants. Past research has demonstrated that (E)-DMNT formation is rate-limited by the initial formation of (3S)-(E)-nerolidol. [2] By introducing strawberry linalool/nerolidol synthase into the mitochondria, however, the researchers generated sizeable amounts of (3S)-(E)-nerolidol, and what’s more, they also discovered that Arabidopsis contains appropriate enzymes for converting (3S)-(E)-nerolidol to (E)-DMNT.

The researchers, then, intentionally infested their transgenic plants with spider mites. Transgenic Arabidopsis heralded more predatory mites due to the augmented volatile profile compared to the wild-type control. When neither (3S)-(E)-nerolidol or (E)-DMNT were created by spider mite attack, predatory mites were not attracted to the plants, and did not come to their rescue.

This study, therefore, validates the fact that plants can communicate when they need help, seeking their own survival, and they can do this through releasing key terpenes. And in a rather beautiful and poetic symbiosis, predatory insects and plants help support each other to better ensure their existence.

 

References

[1] Kappers IF, Aharoni A, van Herpen TW, Luckerhoff LL, Dicke M, Bouwmeester HJ. Genetic engineering of terpenoid metabolism attracts bodyguards to ArabidopsisScience. 2005;309(5743):2070-2072. [journal impact factor = 47.728; times cited = 494]

 

[2] Bouwmeester HJ, Verstappen FW, Posthumus MA, & Dicke M. Spider mite-induced (3S)-(E)-nerolidol synthase activity in cucumber and lima bean. The first dedicated step in acyclic C11-homoterpene biosynthesis. Plant Physiology. 1999;121(1):173-80. [journal impact factor = 8.340; times cited = 144]

 

Image Credit: Vimantha Dilshan, CC BY-SA 4.0, via Wikimedia Commons

About the author

Jason S. Lupoi, Ph.D.

Jason S. Lupoi, Ph.D.

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