过量的硝酸盐会诱导根瘤变绿，并降低大豆血红蛋白的转录本和蛋白表达水平。
Excess nitrate induces nodule greening and reduces transcript and protein expression levels of soybean leghaemoglobins.
机构信息
Root Biology Center, Fujian Agriculture and Forestry University, Fuzhou, China.
出版信息
Ann Bot. 2020 Jun 19;126(1):61-72. doi: 10.1093/aob/mcaa002.
BACKGROUND AND AIMS
Efficient biological nitrogen fixation (BNF) requires leghaemoglobin (Lb) to modulate oxygen pressure in nodules. Excess N supply severely inhibits BNF through effects on Lb during nodulation. As yet, a systematic identification and characterization of Lb-encoding genes in soybean has not been reported.
METHODS
The effects of N on BNF were studied in soybean plants inoculated with rhizobia and exposed to excess or low N availability in hydroponic cultures. To identify soybean Lb proteins, BLAST searches were performed on the Phytozome website. Bioinformatic analysis of identified GmLbs was then carried out to investigate gene structure, protein homology and phylogenetic relationships. Finally, quantitative real-time PCR was employed to analyse the expression patterns of soybean Lb genes in various tissues and in response to high N availability.
KEY RESULTS
Excess N significantly accelerated nodule senescence and the production of green Lb in nodules. In total, seven haemoglobin (Hb) genes were identified from the soybean genome, with these Hb genes readily split into two distinct clades containing predominantly symbiosis-associated or non-symbiotic Hb members. Expression analysis revealed that all of the symbiosis-associated Lbs except GmLb5 were specifically expressed in nodules, while the non-symbiotic GmHbs, GmHb1 and GmHb2, were predominantly expressed in leaves and roots, respectively. Among identified GmLbs, GmLb1-4 are the major Lb genes acting in soybean nodulation, and each one is also significantly suppressed by exposure to excess N.
CONCLUSIONS
Taken together, the results show that excess N inhibits BNF by reducing nodule formation, Lb concentration and nitrogenase activity. The characteristics of the entire Hb family were analysed, and we found that GmLb1-4 are closely associated with nodule development and N2 fixation. This works forms the basis for further investigations of the role of Lbs in soybean nodulation.
背景与目的
高效的生物固氮（BNF）需要豆血红蛋白（Lb）来调节根瘤中的氧压。在结瘤过程中，过量的氮供应会通过对 Lb 的影响严重抑制 BNF。然而，大豆 Lb 编码基因的系统鉴定和表征尚未报道。
方法
在水培培养中，用根瘤菌接种大豆植株并暴露于过量或低氮供应下，研究氮对 BNF 的影响。在 Phytozome 网站上进行 BLAST 搜索，以鉴定大豆 Lb 蛋白。然后对鉴定出的 GmLbs 进行生物信息学分析，以研究基因结构、蛋白质同源性和系统发育关系。最后，采用定量实时 PCR 分析大豆 Lb 基因在不同组织中的表达模式以及对高氮供应的响应。
主要结果
过量的氮显著加速了根瘤的衰老和绿色 Lb 在根瘤中的产生。总共从大豆基因组中鉴定出七个血红蛋白（Hb）基因，这些 Hb 基因很容易分为两个不同的分支，包含主要的共生相关或非共生 Hb 成员。表达分析表明，除 GmLb5 外，所有共生相关的 Lb 都特异性地在根瘤中表达，而非共生的 GmHbs、GmHb1 和 GmHb2 分别主要在叶片和根中表达。在所鉴定的 GmLbs 中，GmLb1-4 是大豆结瘤中主要的 Lb 基因，并且每个基因也都被过量的氮暴露显著抑制。
结论
综上所述，结果表明过量的氮通过减少根瘤形成、Lb 浓度和固氮酶活性来抑制 BNF。对整个 Hb 家族的特征进行了分析，我们发现 GmLb1-4 与根瘤发育和 N2 固定密切相关。这项工作为进一步研究 Lb 在大豆结瘤中的作用奠定了基础。
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