Mild water deficit at seed filling stage promotes drought-tolerant soybean production formation and flavonoids accumulation

Soybean is an important crop for both grain and oil use. Appropriate agricultural managements increase crop productivity quantity and chemical nutrition quality. This study utilized two soybean varieties HN44(droughttolerant) and SN14 (drought-sensitive)to analyze mechanism effect of light drought stress on instantaneous water use efficiency(WUEi), yield and isoflavone content by changes in the transcriptome and metabolome during the early seed-filling stage. The results showed that light drought stress can improve WUEi, stimulate the yield potential and increase the content of Daidzin and 6''-O-malonyldaidzin of HN44. In addition, under light drought stress, the differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in HN44 and SN14 were significantly enriched in the biosynthetic pathways of flavonoids and isoflavones. The flavonoid metabolites in HN44 increased, while those in SN14 decreased. Through the different expression patterns of DEGs and DAMs in the two varieties, differential genes and differential metabolites were screened out, such as CHS, HCT, F3H, HIDH, IF7GT, VR, p-coumaroylquinic, and 6''-O-Malonylglycitin. These genes and metabolites can provide theoretical basis for the selection breeding of drought-tolerant soybean varieties and the evaluation of drought-resistant resources. The findings provided important agronomic strategies for improving the yield, bioactive substances, and water resource management of crop soybeans.