Biosynthetic mechanisms of isoflavone accumulation affected by different growth patterns in Astragalus mongholicus...

At present, Astragalus mongholicus products on the market represent two growth patterns: imitative wild A. mongholicus (WAM) and cultivated A. mongholicus (CAM). The 6-year-old WAM (A6) and 2-year-old CAM (B2) products are often sold as commodities. This study aimed to explore the effects of the abovementioned growth patterns on the biosynthetic mechanisms of isoflavone accumulation in A. mongholicus products.

In this paper, the content of calycosin-7-O-β-D-glucoside in 6-year-old WAM (A6) was significantly higher than that in 2-year-old CAM (B2) based on high-performance liquid chromatography. Tissue anatomy indicated that A6 has developed phloem fibers, thickened secondary walls, and a more well-developed vascular system than B2. Thirteen differentially accumulated metabolites were found in A6 and B2 by UHPLC-ESI-Q-TOF-MS/MS, of which isoflavones were highly and significantly enriched in A6. By combining transcriptomics and metabolomics analysis, we found that the metabolomics profile was the same as the transcriptomics profile in both A6 and B2. In total, 11 novel isoflavone-related genes were isolated using BLAST and functional annotation through RNA-Seq and Iso-Seq. The results of integrated analysis, Short Time-series Expression Miner analysis, and Pearson correlation analysis showed that the regulation of four key enzymes, cinnamate 4-hydroxylase, 6-deoxychalcone synthase, chalcone reductase, and chalcone isomerase, led to the high accumulation of isoflavones in A6. In addition, AmUFGT (c778119) and AmUCGT (c303354) were predicted to be 7-O-glycosyltransferases by phylogenetic analysis; these genes catalyze formononetin and calycosin, respectively.

The findings of this work will clarify the differences in the biosynthetic mechanism of isoflavone accumulation between A6 and B2, which will guide the cultivation of A. mongholicus.