Effect of nitrogen fixation enhancing type <i>SEN1</i> gene on soybean growth

It is well known that the growth of legumes is greatly affected not only by fertilizer nitrogen but also by fixed nitrogen by symbiosis with rhizobia. We have reported that a polymorphism in <i>SEN1</i>, which is essential for nitrogen fixation in <i>Lotus japonicus</i>, could be used to enhance nitrogen fixation and plant growth. In this study, we examined whether the same strategy could be applied to <i>Glycine max</i>. Sequencing of orthologs of the <i>LjSEN1</i> gene in 38 soybean cultivars revealed that the polymorphism occurred at <i>Glyma.08g076300</i>. We defined the standard sequence that most of the cultivars retained as Peking type <i>SEN1</i>, and the mutated sequence found in Enrei as Enrei type <i>SEN1</i>. To investigate the effect of genotype differences, we generated near-isogenic lines by crossing Enrei with Fukuyutaka, which has Peking type <i>SEN1</i>, and analyzed their characteristics. The results showed that Enrei type enhanced nitrogen fixation activity and promoted plant growth. Since soybean SEN1 has been reported to be a homolog of vacuolar iron transporter-like protein, we investigated the iron content in the nodules. In the result, the iron content in the nodules of Enrei type was significantly higher than that of Peking type. Iron is known to be present in the active center of nitrogenase, and the high iron content may have contributed to the increased nitrogen fixation activity. These results suggest that Enrei type <i>SEN1</i> is a nitrogen fixation enhancing gene and that introduction of Enrei type <i>SEN1</i> may reduce nitrogen fertilizer application and increase yield.众所周知，豆科植物（legumes）的生长不仅受化肥氮的影响显著，同时还会受到其与根瘤菌（rhizobia）共生所固定的氮素的调控。我们此前已有研究报道，百脉根（Lotus japonicus）中固氮必需的SEN1基因的多态性可用于提升固氮能力与植物生长。本研究旨在探究相同策略是否可应用于大豆（Glycine max）。对38个大豆栽培品种中LjSEN1基因的直系同源基因进行测序后发现，Glyma.08g076300位点存在多态性。我们将多数栽培品种所保留的标准序列定义为北京型SEN1，而在Enrei品种中发现的突变序列则被命名为Enrei型SEN1。为探究基因型差异的影响，我们将携带Enrei型SEN1的Enrei品种与携带北京型SEN1的Fukuyutaka品种进行杂交，构建了近等基因系（near-isogenic lines），并对其性状进行了分析。结果显示，Enrei型SEN1可提升固氮酶活性并促进植物生长。已有研究表明，大豆SEN1为液泡铁转运蛋白样蛋白的同源蛋白，因此我们对根瘤中的铁含量进行了检测。结果发现，Enrei型SEN1植株根瘤中的铁含量显著高于北京型SEN1植株。众所周知，铁是固氮酶（nitrogenase）活性中心的组成成分，较高的铁含量或许是固氮能力提升的关键原因之一。上述结果表明，Enrei型SEN1是一个固氮增强基因，引入Enrei型SEN1或可减少化肥氮的施用量并提升作物产量。