Advances in biosynthesis, regulation, and metabolic engineering of plant specialized terpenoids

•This review summarizes recent progress in research on plant specialized terpenoids.•This includes formation of universal precursors and different classes of terpenoids and their diversification.•Discoveries of non-canonical routes and gene clusters involved in terpenoid biosynthesis are highlighted.•The review also deals with different aspects of regulation of specialized terpenoids biosynthesis.•Finally, the review covers metabolic engineering strategies employed for overproduction of specialized terpenoids. Plant specialized terpenoids are natural products that have no obvious role in growth and development, but play many important functional roles to improve the plant’s overall fitness. Besides, plant specialized terpenoids have immense value to humans due to their applications in fragrance, flavor, cosmetic, and biofuel industries. Understanding the fundamental aspects involved in the biosynthesis and regulation of these high-value molecules in plants not only paves the path to enhance plant traits, but also facilitates homologous or heterologous engineering for overproduction of target molecules of importance. Recent developments in functional genomics and high-throughput analytical techniques have led to unraveling of several novel aspects involved in the biosynthesis and regulation of plant specialized terpenoids. The knowledge thus derived has been successfully utilized to produce target specialized terpenoids of plant origin in homologous or heterologous host systems by metabolic engineering and synthetic biology approaches. Here, we provide an overview and highlights on advances related to the biosynthetic steps, regulation, and metabolic engineering of plant specialized terpenoids.