Natural variation of GmFNSII-2 contributes to drought resistance by modulating enzyme activity in soybean

As an essential crop that provides vegetable oil and protein, soybean (Glycine max (L.) Merr.) is widely planted all over the world. However, the scarcity of water resources worldwide has seriously impacted on the quality and yield of soybean. To address this, exploring excellent genes for improving drought resistance in soybean is crucial. In this study, we identified natural variations of GmFNSII-2 (flavone synthase II) significantly affect the drought resistance of soybeans. Through sequence analysis of GmFNSII-2 in 632 cultivated and 44 wild soybeans nine haplotypes were identified. The full-length allele GmFNSII-2C, but not the truncated allele GmFNSII-2A possessing a nonsense nucleotide variation, increased enzyme activity. Further research found that GmDREB3, known to increase soybean drought resistance, bound to the promoter region of GmFNSII-2C. GmDREB3 positively regulated the expression of GmFNSII-2C, increased flavone synthase abundance and improved the drought resistance. Furthermore, a single-base mutation in the GmFNSII-2C promoter generated an additional drought response element (CCCCT), which had stronger interaction strength with GmDREB3 and increased its transcriptional activity under drought conditions. The frequency of drought-resistant soybean varieties with Hap 1 (Pro:GmFNSII-2C) has increased, suggesting that this haplotype may be selected during soybean breeding. In summary, GmFNSII-2C could be used for molecular breeding of drought-tolerant soybean