Integrated Metabolomic and Transcriptomic Analysis of Polysaccharide Biosynthesis in Polygonatum odoratum (Mill.) Druce Rhizomes of Different Growth Years and Growth Stages

Polygonatum odoratum (Mill.) Druce is a well-known traditional medicinal plant, with rhizomes as the principal medicinal tissue and polysaccharides as its key bioactive components. To conduct a systematic investigation of the polysaccharide biosynthetic pathway and screen key genes involved in the polysaccharide biosynthesis of different growth years and growth stages in P. odoratum, this study performed transcriptomic and metabolomic analyses on P. odoratum rhizomes of different growth years and growth stages. This study revealed that most saccharides, which serve as precursors for polysaccharide biosynthesis in P. odoratum rhizomes, exhibited higher levels in two-year-old P. odoratum than in three-year-old. Co-expression analysis revealed that PosacA3 showed a high positive correlation with sucrose, D-fructose, and D-glucose, while PoGT16 exhibited a high negative correlation with sucrose, D-fructose, and D-glucose. PoGT6 and PoGT32 displayed a positive correlation with D-glucose and sucrose, respectively, suggesting that these genes may be key regulators involved in polysaccharide biosynthesis in P. odoratum. Compared with two-year-old and three-year-old P. odoratum rhizomes harvested in July and September from Shaodong City, Hunan Province, China, when steroidal saponins and soluble sugars are required as medicinal components, two-year-old P. odoratum can be harvested in July or September. When alkaloids and amino acids and derivatives are the core extraction targets, both two-year-old and three-year-old P. odoratum are recommended to be harvested in September. This study furnishes a theoretical reference for the rational harvesting and utilization of P. odoratum, and lays a foundation for further elucidating its polysaccharide biosynthetic mechanism.