Growth Year and Chemotype Synergistically Regulate Coumarin Accumulation and the Associated Transcriptional Profiles in Peucedanum praeruptorum Dunn

<i>Peucedanum praeruptorum</i> is increasingly cultivated as wild resources are depleted. However, cultivated plants often contain lower levels of coumarins than wild individuals and may not meet the standards of the <i>Chinese Pharmacopoeia</i>. To clarify whether growth year could influence coumarin accumulation, we analyzed <i>P. praeruptorum</i> populations cultivated for 1-3 years using a newly developed 17-coumarin quantification method and conducted transcriptomics to characterize gene expression across growth years. The results suggest that total coumarins and major pyranocoumarins (notably praeruptorin B) increased steadily with growth years, while furanocoumarins and simple coumarins increased initially then declined. Notably, despite substantial intra-population variation in coumarin content, cultivated plants could be classified into two distinct chemotypes: chemotype A (higher praeruptorin A and praeruptorin E, lower praeruptorin B) and chemotype B (lower praeruptorin A and praeruptorin E, higher praeruptorin B, pteryxin, and qianhucoumarin D than chemotype A). Both chemotypes coexisted across all examined populations, with the proportion of chemotype B increasing with growth years. Transcriptomic profiling revealed that 3-year-old plants showed higher expression of pyranocoumarin biosynthetic genes and lower expression of genes associated with simple coumarin and furanocoumarin biosynthesis compared with 1-year-old plants. Differential expression analysis further identified key candidate genes associated with growth years and chemotypes. Together, these results demonstrate that growth year and chemotype synergistically regulate coumarin accumulation in cultivated <i>P. praeruptorum</i>, providing a two-dimensional framework for improving the quality of cultivated medicinal materials.