High-intensity natural sweeteners from four representative plants: Biosynthetic pathways, heterologous production, and molecular markers

Background The rising demand for high-intensity, low-calorie alternatives to sucrose has catalyzed scientific interest in Stevia rebaudiana , Siraitia grosvenorii , licorice ( Glycyrrhiza uralensis , G. inflata , and G. glabra ), and Cyclocarya paliurus . While these plants share a common functional utility, their major sweet constituents differ biochemically: steviol glycosides are ent-kaurane diterpene glycosides, whereas mogrosides, glycyrrhizin, and cyclocariosides are derived from cucurbitane, oleanane, and dammarane-related triterpenoid scaffolds, respectively. Scope and approach This review compares recent advances in genomic resources, biosynthetic pathway elucidation, heterologous production, and molecular marker development across these four botanical groups, emphasizing the functional evidence needed to translate gene discovery into biotechnological and agricultural application. Key findings and conclusions Despite their structural diversity, these compounds share biosynthetic stages involving terpenoid scaffold formation, oxidative modification, and glucosylation or glucuronosylation. While high-quality genome assemblies have substantially expanded candidate gene resources, rigorous experimental verification of these pathways remains limited to specific lineages. Multiple steps in steviol glycoside, mogroside V, and glycyrrhizin biosynthesis have been experimentally characterized, thereby enabling heterologous production to varying degrees of efficiency. By contrast, the specific oxidation and glycosylation reactions leading to cyclocariosides A and I remain largely unresolved. In addition, while trait-linked marker development is most advanced in S. rebaudiana , validated markers to improve sweet-compound traits in other plant groups remain scarce. Overall, comprehensive functional validation of pathway genes and trait-associated variants emerges as the principal requirement for further progress in heterologous production and molecular breeding.