A pivotal switch in β-domain determines the substrate selectivity of terpene synthases involved in Gardenia jasminoides floral scent synthesis

Int J Biol Macromol. 2024 Dec 7:288:138333. doi: 10.1016/j.ijbiomac.2024.138333. Online ahead of print.

Abstract

Plants have evolved a diverse array of secondary metabolites to enhance their adaptability to environmental stresses, with volatile terpenoids being a notable example. Gardenia (Gardenia jasminoides), celebrated for its unique fragrance, is a key natural source of volatile terpenoids. Using our chromosome-level genome and transcriptome data of G. jasminoides, we previously identified six terpene synthases (TPSs) involved in the production of its floral scent. Here, we functionally characterized these six key TPS enzymes, aligning their product profiles with volatile organic compound (VOC) analysis. Notably, we identified two highly similar TPSs, GjTPS1 and GjTPS2, which share high sequence homology but differ in substrate selectivity. Through AI-based predictions and site-directed mutagenesis, we pinpointed a single amino acid in the β-domain that acts as a "switch," modulating substrate selectivity-an unusual finding, as this residue is outside the active site region. Comparative genomic analyses with Coffea canephora and other eudicots revealed that G. jasminoides TPS genes primarily expanded through dispersed duplications (DSD) and tandem duplications (TD). Our study is the first to reveal a "switch" in a previously deemed "non-functional" region, regulating substrate selectivity in TPS proteins. These insights could facilitate breeding elite Gardenia varieties and support the rational engineering of terpene synthases.

Keywords: Dispersed duplication; Gardenia jasminoides; Site-directed mutagenesis; Substrate selectivity; Tandem duplication; Terpene synthases.