Identification and characterization of terpene synthase genes accounting for volatile terpene emissions in the flower of Paeonia lactiflora

Abstract

Emergence of floral scents marked a significant milestone in biological development of plant, letting out olfactory signals that enable them to induce pollinators. In this research, molecular and metabolomics methodologies were used to explore terpene synthase (TPS) genes, which are responsible for synthesis of floral fragrance in Paeonia lactiflora ‘Wu Hua Long Yu’. Analyses on transcriptome data identified 11 PlTPS genes, among them 7 genes were isolated, and the functions of 5 genes were confirmed. PlTPS1 was identified as a single-product enzyme; PlTPS4, 8 and 9 were identified as bifunctional enzymes, capable of recognizing farnesyl pyrophosphate and geranyl pyrophosphate; PlTPS6 generated multiple products by recognizing farnesyl pyrophosphate. Enzymatic products of these PlTPS proteins closely matched the volatile terpenes emitted by flowers, revealing the relation between PlTPS genes and the release of such volatile compounds. Functions of five PlTPS genes in herbaceous peony were further elucidated through virus-induced gene silencing experiments, as well as overexpression in tobacco. PlTPS1 catalyzes geraniol production, while PlTPS4 catalyzes linalool. PlTPS6 is responsible for producing two sesquiterpenes, caryophyllene and α-humulene. PlTPS8, with the most varied products, mainly catalyzes the production of α-pinene, linalool, and germacrene D. Based on these findings, graphical models summarizing the biosynthesis of floral volatile terpenes in herbaceous peony have been proposed. The characterization of PlTPS genes has elucidated their specific roles in the synthesis of herbaceous peony fragrance, opening up possibilities for introducing or enhancing floral scents in herbaceous peony and other plants.