Biosynthesis of modular signaling molecules requires functional diversification of carboxylesterases in Pristionchus pacificus

Abstract

The model nematode Pristionchus pacificus produces four types of complex ascaroside pheromones named UBAS, DASC, NPAR, and PASC. However, the exact biosynthetic pathways of these modular signaling molecules remain enigmatic. We have previously identified a carboxylesterase Ppa-UAR-1 for the biosynthesis of UBAS, enabling the attachment of ureidoisobutyric acid at the 4-position of simple ascarosides. Here, we report three new carboxylesterases Ppa-UAR-5, Ppa-UAR-6 and Ppa-UAR-12 from P. pacificus. Ppa-UAR-5 functions downstream of Ppa-UAR-1 to furnish the biosynthesis of ubas#1 and ubas#2, whereas Ppa-UAR-12 specifically links two ascr#1 at the 4-position to synthesize dasc#1. Finally, Ppa-UAR-6 is essential for the biosynthesis of npar#1-3 and part#9. The expression patterns of Ppa-uar-6 and Ppa-uar-12 in the intestinal and epidermal cells suggest pheromone biosynthesis to be restricted to specific tissues. These findings indicate that the expansion and functional diversification of carboxylesterases plays a crucial role in the evolution of complex pheromones in nematodes. SIGNIFICANCEOur study identified three new carboxylesterase genes (Ppa-uar-5, Ppa-uar-12 and Ppa-uar-6) from P. pacificus. The encoded enzymes separately regulated the biosynthesis of three types of modular pheromones (UBAS, DASC, and NPAR-types) in worms intestinal cells and exhibited extremely high substrate-specificity. For example, we verified that Ppa-UAR-12 specifically linked one ascr#1 to the 4-position of another ascr#1 to finally furnish the biosynthesis of ascaroside dimer dasc#1. These new discoveries largely clarify the delicate biosynthetic mechanisms of how diversification of carboxylesterases functions in P. pacificus to build up enormous complexity of modular signaling molecules. Such a biosynthetic mechanism of nematode pheromones might be widely conserved in the phylum Nematoda.