AsianScientist (Apr. 13, 2026)–That fresh, sharp scent released when grass is cut is often associated with calm and nostalgia, but beneath this sensory experience lies a sophisticated biological signal. These compounds, known as green leaf volatiles (GLVs), are released by plants within seconds of being wounded, attacked by herbivores, or exposed to environmental stress.
GLVs are active participants in plant defense. They suppress pathogens, warn neighbouring plants to prepare for attack, and attract the natural enemies of herbivores feeding on them. This intricate chemical signaling system highlights the complexity of plant behaviour.
A new study led by Yu-Hsien Lin, Assistant Professor in the Global Agricultural Technology and Genomic Science Program, at National Taiwan University, along with collaborators, including Assistant Professor Ching-Wen Tan from the Department of Entomology at National Chung Hsing University, sheds light on how this chemical communication has evolved.
“The study connects plant and insect physiology, chemical ecology, molecular function, and evolutionary analysis to offer a new perspective on plant–insect coevolution,” says Yu-Hsien Lin, commenting on the study published in Nature Ecology & Evolution.
Central to the study is an enzyme known as hexenal isomerase (Hi), found in both plants and certain insects – particularly lepidopterans such as moths and butterflies.
The researchers discovered that Hi enzymes in lepidopteran saliva can convert Z-3-hexenal, one of the earliest GLVs released by wounded plants, into E-2-hexenal, thereby altering the composition of plant-emitted volatiles. Because increased E-2-hexenal may more effectively attract the natural enemies of caterpillars, this transformation can effectively amplify the plant’s alarm signal while the insect is feeding.
Plants too possess their own versions of Hi enzymes capable of catalyzing the same reaction. However, plant and insect enzymes arise from entirely different protein families, showing that they evolved similar functions independently, through distinct evolutionary routes.
The team analyzed 34 species of Lepidoptera and found that insect Hi is largely restricted to more recently diversified lineages, suggesting that this function was not broadly present early in lepidopteran evolution but emerged gradually in specific groups.
The study also revealed significant variation in enzyme activity across species, pointing to ongoing evolutionary fine-tuning. To probe deeper into how these enzymes function, the researchers used AlphaFold, an artificial intelligence system developed by Google DeepMind, to predict protein structures. Combined with functional analyses, this helped clarify the catalytic mechanisms underlying Hi activity.
On the plant side, molecular evolutionary analyses suggest that plant-specific Hi enzymes originated in mesangiosperms, a major group of flowering plants. Their emergence appears to be closely tied to the ecological transformations brought about by the diversification of flowering plants.
“The next time we notice the familiar scent of freshly cut grass, it may be worth remembering that this is not just the smell of plants—it may also be a chemical distress signal, and a trace of a plant–insect arms race that has unfolded over millions of years,” says Yu-Hsien Lin.
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Source: National Taiwan University; Image: Reflex-Ajans_Freepik
The article can be found at: Convergent evolution of hexenal isomerases in Lepidoptera and plants
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