A dual-localized geraniol synthase and a previously unreported cytosolic geranyl pyrophosphatase contribute to geraniol formation in lemongrass

Geraniol, a major constituent of many essential oils and precursor for geraniol-derived aldehydes and acetates, is produced in plants through the action of a terpene synthase encoding geraniol synthase or via terpene synthase-independent non-canonical pathway involving a Nudix hydrolase and a yet to be discovered pyrophosphatase. Here, we identify a geraniol synthase (Cymbopogon flexuosus geraniol synthase; CfGES) that catalyzes the conversion of geranyl pyrophosphate (GPP) (also known as geranly diphosphate) to geraniol, as well as a previously unreported geranyl pyrophosphatase (CfG(P)Pase) that acts on both GPP and geranyl monophosphate (GP), albeit with different efficiencies, to generate geraniol. Virus-induced gene silencing of CfGES or CfG(P)Pase resulted in a substantial reduction in geraniol and its immediate product citral in lemongrass leaves. Conversely, transient overexpression of CfGES or CfG(P)Pase resulted in enhanced production of geraniol and citral in lemon balm (Melissa officinalis) leaves, as well as geraniol, citronellol, and citral in rose (Rosa damascena) flower petals. Subcellular localization studies revealed that while CfGES exhibited dual cytosolic/plastidial localization, CfG(P)Pase was localized to the cytosol. This localization pattern was further supported by the significantly higher geraniol-forming activity observed in the purified cytosolic protein fraction compared to the chloroplast fraction. Our study uncovers the missing step in cytosolic geraniol formation via a TPS-independent non-canonical route and demonstrates that geraniol, required for citral production in lemongrass, is synthesized by cytosolic CfG(P)Pase and cytosol-/plastid-localized CfGES.