Integrated metabolomic and transcriptomic analysis of specialized metabolites and isoflavonoid biosynthesis in Sophora alopecuroides L. under different degrees of drought stress

Appropriate drought stress could promote the accumulation of specialized metabolites in plants, especially in medicinal plants. Sophora alopecuroides L. (Leguminosae), a medicinal plant with a variety of bioactive specialized metabolites, has an excellent drought resistance. In this study, drought stress-induced metabolomic and transcriptomic changes in S. alopecuroides were identified, to explore the mechanism of specialized metabolite changes in response to mild, moderate and severe drought stress. The metabolic analysis results showed that a total of 919 annotated metabolites were detected and quantified, of them, flavonoid metabolites were the main metabolites in S. alopecuroides. Moreover, a total of 411 differentially accumulated metabolites (DAMs) were identified, among them, 6-Hydroxydaidzein, 2-Hydroxy-2,3-dihydrogenistein, prunetin, and bio-chanin A significantly increased under mild drought stress but isoflavonoids significantly decreased under moderate and severe drought stress. Transcriptional analysis showed that a total of 21,307 differentially expressed genes (DEGs) were identified, and most of them were enriched in the biosynthesis of secondary me-tabolites pathway. The integrated metabolomic and transcriptomic analyses results proved that these DAMs and DEGs were most significantly enriched in isoflavonoid biosynthesis pathway (ko00943). In addition, some structural genes such as 2-hydroxyisoflavanone synthase (IFS), 2-hydroxyisoflavanone dehydratase (HID), iso-flavone 7-O-glucosyltransferase (IF7GT), and isoflavone 7-O-glucoside-6"-O-malonyltransferase (IF7MAT) and seven MYB transcription factors (SaMYB1 similar to SaMYB7) were identified, which played crucial regulatory roles in the isoflavonoid synthesis. This study provides useful insights into the molecular mechanism of S. alopecuroides in response to drought stress, and help develop biotechnological strategies to manipulate the levels of therapeutic specialized metabolites in S. alopecuroides.