Asarum fudsinoi is one of several plant species whose flowers have a distinctive foul odour, reminiscent of decaying flesh, that attracts pollinators specialized to oviposit on decomposing materials. Writing in Science, Okuyama and colleagues explored the genetic and physiological mechanisms that enable plants to exhibit this form of floral mimicry. The volatile blends emitted by Asarum flowers are dominated by oligosulfides such as dimethyl disulfide (DMDS), which is derived from an organosulfur compound known as methanethiol. The authors performed enzymatic assays and phylogenetic analysis to show that Asarum species have independently evolved floral scents with high DMDS content, and that DMDS emission is closely correlated with high expression levels of genes that encode selenium-binding proteins (SBPs). Reconstruction of ancestral protein sequences and recombinant protein assays revealed that, similar to the SBPs of animals and prokaryotes, the SBP2 protein in land plants oxidizes methanethiol to produce hydrogen sulfide, which indicates that this enzymatic function is probably conserved across prokaryotes and eukaryotes. Independent gene duplication events gave rise to the SBP1 gene in three genera with high levels of DMDS emission — Asarum, Eurya and Symplocarpus. The SBP1 proteins encoded by these genes share two or three amino acid substitutions and have lost the ability to oxidize methanethiol, but have gained disulfide synthase activity (which converts methanethiol to DMDS). The authors conclude that repeated gene duplication and co-option of a highly conserved metabolic pathway has facilitated the evolution of floral mimicry.
Original reference: Science 388, 656–661 (2025)
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