Diversity and Functional Evolution of Terpene Synthases in Dictyostelid Social Amoebae

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 species-adaptive biological functions as chemical languages in dictyostelids.

A terpene synthase-cytochrome P450 cluster in Dictyostelium discoideum produces a novel trisnorsesquiterpene

“…As mentioned earlier, D. purpureum is related to D. discoideum and its TPS family has been comprehensively characterized in our recent study (Chen et al, 2018). For comparison, we also analyzed the CYP family in D. purpureum and searched for putative TPS-CYP clusters in this species.…”

“…It is equally intriguing to observe that D. purpureum contains two TPS-CYP clusters (Figure 7B). With the evolutionary relationship of TPS genes from D. discoideum and D. purpureum recently determined (Chen et al, 2018), we are able to examine the relatedness of these TPS-CYP gene clusters. The ortholog of DdTPS8 in D. purpureum is DpTPS6 (Chen et al, 2018), which is not clustered with any CYP gene.…”

“…With the evolutionary relationship of TPS genes from D. discoideum and D. purpureum recently determined (Chen et al, 2018), we are able to examine the relatedness of these TPS-CYP gene clusters. The ortholog of DdTPS8 in D. purpureum is DpTPS6 (Chen et al, 2018), which is not clustered with any CYP gene. Moreover, D. purpureum lacks an ortholog of CYP521A1 , implying that the D. purpureum may not produce discodiene, consist with the volatile profiling of this species (Chen et al, 2018).…”

“…Dictyostelium discoideum and D. purpureum are among the most extensively investigated species of dictyostelid social amoebae. Our recent studies illustrated that the multicellular stages of the life cycle of both D. discoideum (Chen et al, 2016) and D. purpureum (Chen et al, 2018) are characterized by the emission of a complex mixture of volatile organic compounds that is dominated by sesquiterpenes. While some terpenoids are produced by both species, most appear to be species-specific (Chen et al, 2018).…”

Small molecules and cell differentiation in Dictyostelium discoideum

“…Recent findings indicate a wider distribution of TPS genes in social amoeba (Chen et al, 2016). For example, D. discoideum has 11 putative TPS genes in its genome, of which 9 are full-length sequences, while D. purpureum genome contains 12 functional TPS genes (Chen et al, 2018). Based on the profiling of volatile compounds by solid-phase microextraction followed by gas chromatography-mass spectrometry, no evidence of volatile terpenes was detected at t0 stage of D. discoideum development.…”