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

<i>Polygonatum odoratum</i> (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 <i>P. odoratum</i>, this study performed transcriptomic and metabolomic analyses on <i>P. odoratum</i> rhizomes of different growth years and growth stages. This study revealed that most saccharides, which serve as precursors for polysaccharide biosynthesis in <i>P. odoratum</i> rhizomes, exhibited higher levels in two-year-old <i>P. odoratum</i> than in three-year-old. Co-expression analysis revealed that <i>PosacA3</i> showed a high positive correlation with sucrose, D-fructose, and D-glucose, while <i>PoGT16</i> exhibited a high negative correlation with sucrose, D-fructose, and D-glucose. <i>PoGT6</i> and <i>PoGT32</i> displayed a positive correlation with D-glucose and sucrose, respectively, suggesting that these genes may be key regulators involved in polysaccharide biosynthesis in <i>P. odoratum</i>. Compared with two-year-old and three-year-old <i>P.</i> 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 <i>P. odoratum</i> 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 <i>P. odoratum</i> are recommended to be harvested in September. This study furnishes a theoretical reference for the rational harvesting and utilization of <i>P. odoratum</i>, and lays a foundation for further elucidating its polysaccharide biosynthetic mechanism.