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Abstract:
Dictyostelids, or social amoebae, have a unique life style in forming multicellular fruiting bodies from
unicellular amoeboids upon starvation. Recently, dictyostelids were found to contain terpene synthase
(TPS) genes, a gene type of secondary metabolism previously known to occur only in plants, fungi and
bacteria. Here we report an evolutionary functional study of dictyostelid TPS genes. The number of TPS
genes in six species of dictyostelids examined ranges from 1 to 19; and the model species Dictyostelium
purpureum contains 12 genes. Using in vitro enzyme assays, the 12 TPS genes from D. purpureum were
shown to encode functional enzymes with distinct product profiles. The expression of the 12 TPS genes
in D. purpureum is developmentally regulated. During multicellular development, D. purpureum releases
a mixture of volatile terpenes dominated by sesquiterpenes that are the in vitro products of a subset of
the 12 TPS genes. The quality and quantity of the terpenes released from D. purpureum, however, bear
little resemblance to those of D. discoideum, a closely related dictyostelid. Despite these variations,
the conserved clade of dictyostelid TPSs, which have an evolutionary distance of more than 600 million
years, has the same biochemical function, catalyzing the formation of a sesquiterpene protoillud-7-ene.
Taken together, our results indicate that the dynamic evolution of dictyostelid TPS genes includes both
purifying selection of an orthologous group and species-specific expansion with functional divergence.
Consequently, the terpenes produced by these TPSs most likely have conserved as well as speciesadaptive
biological functions as chemical languages in dictyostelids.
