A flower sways in a gentle breeze, its smell attracting pollinators from hundreds of meters away. Unlike roses and gardenias, which emanate a sweet fragrance, certain flowers have embraced the aroma of decay. Species such as Amorphophallus titanium, known for producing the world’s largest floral structure, lure insects with a stench that resembles carrion and dung.1 Mistaking the flowers for places to lay eggs, insects that thrive on decaying matter land on these stinky blossoms, thus aiding their pollination. Now, in a study published in Science, researchers have sniffed out the genetic and molecular mechanisms behind this olfactory deception.2
A common feature of carrion-mimicking flowers is the secretion of malodorous volatile blends dominated by oligosulfides.3 Scientists have previously shown that plants produce these pungent compounds from methanethiol, a product of breaking down the amino acid methionine.4 Methanethiol is also present in the human body, where bacteria degrade it to secrete oligosulfides in the mouth and gut, which can lead to bad breath. Atsushi Nagano, a plant biologist at Ryukoku University, wanted to understand if stinky plants utilize the same molecular mechanisms as animals to produce their characteristic smell. He hypothesized that specific enzymes could drive the differences in the strength of the odor between different plant species. To investigate this, Nagano and his team experimented with the malodorous Asarum plant. An analysis of the transcriptome of 26 Asarum species revealed a strong correlation between the gene encoding for selenium-binding proteins (SBPs) and the abundance of oligosulfides in the flowers.
Carrion-mimicking flowers produce oligosulfides to deceive insects into pollinating them.
© 2025, National Museum of Nature and Science
In humans, SBPs detoxify methanethiol into less harmful or putrid substances.5 Curious to know why carrion-mimics had higher expression of these proteins, Nagano and his team tested the function of plant SBPs by introducing three identified genes into engineered bacteria: SBP1, SBP2, and SBP3. Instead of breaking down methanethiol, the plant SPBs, specifically the SBP1 variant, clustered it to produce pungent oligosulfides.
How did the ancestral function of these proteins evolve into something new? A phylogenetic comparison of the ancestral methanethiol detoxifier and SBP1 revealed substitutions at three amino acid sites. Instead of detoxification, SBP1’s function shifted to become an oligosulfide factory, thus enabling these stink bombs to carve an ecological niche for themselves. However, this evolutionary trait was not present in all oligosulfide-producing plants. Among the 12 genera tested, only three—Asarum, Symplocarpus, and Eurya—showed enzyme activity, all of which gained the protein through gene duplication events. These findings raise new questions about how and why some plants evolve floral mimicry with strong, pungent scents.
- Claudel C, Lev-Yadun S. Odor polymorphism in deceptive Amorphophallus species - a review: Odor polymorphism in Amorphophallus. Plant Signaling & Behavior. 2021;16(12):1991712.
- Okuyama Y, et al. Convergent acquisition of disulfide-forming enzymes in malodorous flowers. Science. 2025.
- Stensmyr MC, et al. Rotting smell of dead-horse arum florets. Nature. 2002;420(6916):625-626.
- Rébeillé F, et al. Methionine catabolism in Arabidopsis cells is initiated by a γ-cleavage process and leads to S-methylcysteine and isoleucine syntheses. Proc Nat Acad Sci USA. 2006;103(42):15687-15692.
- Pol A, et al. Mutations in SELENBP1, encoding a novel human methanethiol oxidase, cause extraoral halitosis. Nat Genet. 2018;50(1):120-129.
