Evaluation of Drought Resistance in Soybean Germplasm and Identification of Candidate Drought-Resistant Genes

In order to provide theoretical basis for molecular breeding of soybean drought resistance, the different evaluation indexes of drought resistance were comprehensively used to screen soybean germplasm with drought-resistance, and the candidate drought-tolerant genes were identified.

In 2018, 2019, 2020 and 2021, a total of 188 soybean germplasm were used to determine pod number per plant, biomass per plant and yield per plant under well-watered and drought stressed conditions. Drought resistance index (DI), improved drought resistance index (IDI), weighted drought resistance coefficient (WDC) and weighted drought resistance index (WDI) were used to identify drought resistance of soybean germplasm. The single nucleotide polymorphisms (SNP) loci significantly associated with these parameters were detected by genome-wide association study (GWAS), and the candidate genes for drought resistance were screened by RNA-seq and qRT-PCR analysis of soybean seedling leaves under drought stress.

The DI, IDI, WDC and WDI of 188 soybean germplasm varied widely, and five classification criteria for each drought resistance parameter were determined by hierarchical classification method. Among them, Liaodou 15, Liaodou 69, Liaodou 14, Jinzhangzi Huangdou, Zhonghuang 606, Kexin 3 and Koreane 4 were identified as first-grade drought resistant by all evaluation methods. By using GWAS for DI, IDI, WDC and WDI, a total of 15 significantly SNP loci were detected under multiple environments, and the contribution rate of these loci to phenotypic variation ranged from 12.46% to 25.60%. There are 226 annotated genes within 200 kb intervals of upstream and downstream for the significant SNP loci. According to RNA-seq and qRT-PCR analysis of drought-resistant cultivar Liaodou 14 and drought-sensitive cultivar Liaodou 21 under drought stress, a total of 32 annotated genes were significantly differentially expressed by drought stress. Among them, eight genes including Glyma.02G182900, Glyma.04G012400, Glyma.06G258900, Glyma.15G100900, Glyma.01G172600, Glyma.04G012300, Glyma.01G172200 and Glyma.04G010300, encodes calcium-dependent protein kinase, universal stress protein A-like protein, G-type lectin S-receptor-like serine/threonine-protein kinase, protein phosphatase 2C, isoflavone reductase, isoflavone reductase homolog, auxin-like protein, and bZIP transcription factor, respectively.

Seven germplasm were identified from 188 soybean germplasm by comprehensive application of different drought tolerance parameters. A total of 15 SNP loci significantly associated with drought tolerance parameters were identified by GWAS, and eight candidate genes were identified.