Data from: Improvement in nitrogen fixation capacity could be part of the domestication process in soybean

Biological nitrogen fixation (BNF) in soybeans is a complex process involving the interplay between the plant host and the symbiotic rhizobia. As nitrogen supply has a crucial role in growth and development, higher nitrogen fixation capacity would be important to achieve bigger plants and larger seeds, which were important selection criteria during plant domestication by humans. To test this hypothesis, we monitored the nitrogen fixation-related performance in 31 cultivated and 17 wild soybeans after inoculation with the slow-growing Bradyrhizobium diazoefficiens sp. nov. USDA110 and the fast-growing Sinorhizobium (Ensifer) fredii CCBAU45436. Our results showed that, in general, cultivated soybeans gave better performance in BNF. Electron microscopic studies indicated that there was an exceptionally high accumulation of poly-β-hydroxybutyrate bodies in bacteroids in the nodules of all wild soybeans tested, suggesting that the C/N balance in wild soybeans may not be optimized for nitrogen fixation. Furthermore, we identified new quantitative trait loci (QTLs) for total ureides and total nodule fresh weight by employing a recombinant inbred population composed of descendants from a cross between a cultivated and a wild parent. Using nucleotide diversity (θπ), divergence index (Fst) and distribution of fixed single-nucleotide polymorphisms as parameters, we found that some regions in the total ureides QTL on chromosome 17 and the total nodule fresh weight QTL on chromosome 12 exhibited very low diversity among cultivated soybeans, suggesting that these were traits specially selected during the domestication and breeding process.

大豆生物固氮（Biological nitrogen fixation, BNF）是宿主植物与共生根瘤菌相互作用的复杂过程。氮供应对植物生长发育至关重要，更高的固氮能力对于培育更大植株、更饱满种子具有重要意义，而这也是人类开展植物驯化时的重要选择标准。为验证这一假说，本研究对31份栽培大豆及17份野生大豆分别接种慢生型大豆慢生根瘤菌（Bradyrhizobium diazoefficiens）新种USDA110与快生型费氏中华根瘤菌（Sinorhizobium (Ensifer) fredii）CCBAU45436，监测其固氮相关性状表现。结果显示，总体而言栽培大豆的固氮表现更优。电子显微镜研究表明，所有供试野生大豆的根瘤类菌体中均异常积累聚β-羟基丁酸酯颗粒，提示野生大豆的碳氮比可能未优化至适宜固氮的状态。此外，本研究利用栽培大豆与野生大豆杂交构建的重组自交系群体，鉴定出与总尿囊素类物质含量及根瘤总鲜重相关的全新数量性状位点（quantitative trait loci, QTLs）。通过以核苷酸多样性（θπ）、分化指数（Fst）以及固定单核苷酸多态性的分布作为分析参数，本研究发现17号染色体上的总尿囊素类物质QTL区域与12号染色体上的根瘤总鲜重QTL区域在栽培大豆中呈现极低的遗传多样性，表明这两类性状是驯化与育种过程中受到定向选择的目标性状。