The evolutionary secret of rotten-smelling flowers that seduce pollinators
Science News, May 8 (EFEverde).- Not all plants attract pollinators with sweet fragrances; some do so with tremendous odors. Now, a study published in Science explains how a plant gene has evolved to produce unpleasant odors and obtain ecological advantages.
Led by Yudai Okuyama, an evolutionary biologist at the University of Tokyo and the National Museum of Nature and Science in Japan, and conducted by a dozen Japanese research centers, the study demonstrates how plants are able to emit unpleasant odors to attract pollinators.
Emitting fragrances can encourage insects to visit the plant's reproductive organs and thus increase the chances of pollination, but they can also repel unwanted visitors.
Throughout evolution, plants have modulated the molecular composition of these odors to attract certain insects.
The study explains that in the flowers of Asarum, or wild ginger, a gene designed to detoxify odorous compounds has evolved to produce unpleasant odors, a finding that sheds light on how plants use ancient metabolic pathways for ecological advantage.
According to the study, these plants use chemicals (oligosulfides) that give their flowers a smell similar to that of a rotting corpse to trick insects that feed on decaying organic matter into visiting them and achieving pollination.
Smelly volatile compoundsA key feature of malodorous flowers is the release of malodorous volatile compounds, particularly oligosulfides such as dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS).
These compounds mimic the chemical signals emitted by decomposing material.
Although these compounds are known to be formed from the bacterial breakdown of sulfur-containing amino acids, the biological mechanisms that allow flowers to produce them remain largely unknown.
To learn more about this question, Yudai Okuyama studied flowers of the genus Asarum , which have a remarkable diversity of shapes and scents, traits thought to have evolved to attract as many pollinators as possible.
Using comparative genomics and functional assays, Okuyama and his team discovered that floral DMDS emission is linked to the expression of a gene in the selenium-binding protein family.
In humans, the related protein, SELENBP1, normally detoxifies methanethiol, a strong-smelling compound linked to clinical bad breath. This protein detoxifies methanethiol, converting it into less harmful substances.
In Asarum species , Okuyama and colleagues found three distinct types of methanethiol oxidase genes: SBP1, SBP2 , and SBP3 .
By expressing these genes in bacteria and testing their enzymatic function, they discovered that SBP1 performs a unique reaction: instead of detoxifying methanethiol, it transforms it into DMDS.
This ability arose through a small number of amino acid changes in SBP1 that altered the enzymatic function of SBP1 from a methanethiol oxidase (MTOX) to a disulfide synthase (DSS).
The authors believe this ability has evolved independently in at least three plant lineages unrelated to Asarum , suggesting convergent evolution driven by similar ecological pressures, the study notes.
In a related perspective published in Science and titled "flowers with bad breath," Lorenzo Caputi and Sarah O'Conner of the Max Planck Institute for Chemical Ecology note that "it is remarkable" that while methanethiol oxidation is also observed in humans, "oligosulfide synthase enzymatic activity has only evolved in plants."
Researchers believe this may be because "plants are under constant evolutionary pressure to produce complex chemistry for communication and defense."
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