Not all plants attract pollinators by smelling sweet. Some stink like rotting meat or even dung. Those odors can attract flies that will pollinate them. This stench comes from bacteria feasting on rotting corpses. How plants make such a foul smell has been a mystery — until now.
Scientists in Japan looked at DNA in three unrelated groups of stinky plants. All had all evolved the same trick to produce this reeking scent. It involved tweaking one gene. (Genes are bits of DNA related to certain traits.)
The team shared its findings May 8 in Science.
First, the stinky plants all made an extra copy of a gene called SBP1. This gene makes an enzyme. It helps break down a chemical called methanethiol (Meth-an-ETH-ee-awl). This molecule is already fairly smelly. It can build up in the mouths of some people who don’t regularly brush their teeth. An oral condition can develop called halitosis, in which someone’s breath becomes really stinky.
The extra copy of SBP1 in the stinky plants is altered, or mutated. The affected gene now makes its enzyme with a few different amino acids in it. In some plants, three amino acids in this enzyme have been changed. Those plants include a type of wild ginger and the East Asian eurya shrub. In the Asian skunk cabbage, meanwhile, only two amino acids are changed.
But those tiny changes have big impacts. The altered SBP1 enzyme no longer breaks down methanethiol. Instead, it links two of these molecules into dimethyl disulfide. That chemical is to blame for the much more putrid scent of rotten meat. It’s also one of the chemicals responsible for the intense reek of the corpse flower (although the main ones there are putrescine and dimethyl trisulfide).
What benefit do plants get from making the foul-smelling molecule? They may attract more flies to pollinate them, the researchers found.
Gene duplication — like these plants did with SBP1 — is pretty common. It has happened in the evolution of most life-forms, including humans.
Flawed extra copies of genes become the sources of new traits in many species. The reason is that copies of genes can mutate without harming the original gene. This allows species to try out new traits without losing their old ones.