Advances in engineering microalgae for heterologous terpenoid synthesis: A review

Terpenoids are a class of natural products widely distributed in living organisms, with isoprene as their fundamental structural unit. However, traditional plant extraction and chemical synthesis methods are often limited by low product purity, difficult separation, and complex synthetic steps, making it challenging to meet the demands of large-scale production. Conventional hosts such as Escherichia coli and Saccharomyces cerevisiae are utilized for terpenoid synthesis due to their advantages of short growth cycles and controllable cultivation conditions. Nevertheless, the complexity of terpenoid biosynthetic pathways poses significant challenges for these hosts in producing structurally complex terpenoids. In contrast, microalgae as photosynthetic microorganisms, possess well-developed endogenous terpenoid metabolic pathways, abundant precursor pools, and subcellular structures and regulatory mechanisms similar to those of plants, demonstrating significant advantages in the heterologous production of complex terpenoids. This review systematically summarizes recent advances in the production of heterologously synthesized terpenoids in eukaryotic microalgae, ranging from monoterpenes to triterpenes, and provides an in-depth analysis of key engineering strategies, including MEP/MVA pathway regulation, gene expression optimization, subcellular compartmentalization, and cultivation process intensification. In addition, the application potential of advanced tools such as CRISPR/Cas, microalgae-microorganism co-culture, and artificial intelligence is introduced. Finally, the major bottlenecks faced by microalgae as a sustainable green cell factory for terpenoid production are briefly analyzed, and future research directions are proposed.