Research progress on biosynthesis and regulation of monoterpenoid compounds.

Monoterpenoids are an important class of plant volatile natural products with broad applications in the food, fragrance, pharmaceutical, and agricultural industries. However, their conventional production largely relies on plant extraction, which is often constrained by low efficiency, high cost, and limited sustainability. Structurally, monoterpenoids can be classified into acyclic, monocyclic, and bicyclic types, and their structural diversity is closely associated with differences in biosynthetic routes and regulatory mechanisms. Their biosynthesis depends on precursor supply from the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways, followed by terpene synthase (TPS)-mediated scaffold formation and subsequent modification reactions. In addition, monoterpenoid accumulation is regulated by multiple factors, including environmental cues, phytohormone signaling, transcriptional regulation, and epigenetic or post-transcriptional control. Meanwhile, substantial progress has been made in the heterologous production of monoterpenoids in microbial platforms such as Escherichia coli and Saccharomyces cerevisiae through metabolic engineering and synthetic biology. This review summarizes recent advances in monoterpenoid biosynthesis, multilevel regulation, and heterologous production, with particular emphasis on major bottlenecks and optimization strategies for sustainable and efficient biomanufacturing.