Legume–rhizobia symbiosis enables biological nitrogen fixation to improve crop production for sustainable agriculture. Small heat shock proteins (sHSPs) are involved in multiple environmental stresses and plant development processes. However, the role of sHSPs in nodule development in soybean remains largely unknown. In the present study, we identified a nodule-localized sHSP, called GmHSP17.9, in soybean, which was markedly up-regulated during nodule development. GmHSP17.9 was specifically expressed in the infected regions of the nodules. GmHSP17.9 overexpression and RNAi in transgenic composite plants and loss of function in CRISPR-Cas9 gene-editing mutant plants in soybean resulted in remarkable alterations in nodule number, nodule fresh weight, nitrogenase activity, contents of poly β-hydroxybutyrate bodies (PHBs), ureide and total nitrogen content, which caused significant changes in plant growth and seed yield. GmHSP17.9 was also found to act as a chaperone for its interacting partner, GmNOD100, a sucrose synthase in soybean nodules which was also preferentially expressed in the infected zone of nodules, similar to GmHSP17.9. Functional analysis of GmNOD100 in composite transgenic plants revealed that GmNOD100 played an essential role in soybean nodulation. The hsp17.9 lines showed markedly more reduced sucrose synthase activity, lower contents of UDP-glucose and acetyl coenzyme A (acetyl-CoA), and decreased activity of succinic dehydrogenase (SDH) in the tricarboxylic acid (TCA) cycle in nodules due to the missing interaction with GmNOD100. Our findings reveal an important role and an unprecedented molecular mechanism of sHSPs in nodule development and nitrogen fixation in soybean.

中文翻译：

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来自根瘤的小热休克蛋白 GmHSP17.9 赋予大豆共生固氮和种子产量

豆科植物-根瘤菌共生使生物固氮能够改善可持续农业的作物生产。小型热休克蛋白 (sHSP) 涉及多种环境压力和植物发育过程。然而，sHSPs 在大豆根瘤发育中的作用仍然很大程度上未知。在本研究中，我们在大豆中发现了一种定位于根瘤的 sHSP，称为GmHSP17.9，它在根瘤发育过程中显着上调。GmHSP17.9在结节的感染区域特异性表达。GmHSP17.9转基因复合植物中的过表达和 RNAi 以及大豆中 CRISPR-Cas9 基因编辑突变体植物的功能丧失导致根瘤数量、根瘤鲜重、固氮酶活性、聚 β-羟基丁酸小体 (PHB) 含量、脲和总氮含量，引起植物生长和种子产量的显着变化。还发现 GmHSP17.9 作为其相互作用伙伴 GmNOD100 的伴侣，GmNOD100 是大豆根瘤中的一种蔗糖合酶，它也优先在根瘤的感染区表达，类似于GmHSP17.9。GmNOD100在复合转基因植物中的功能分析表明，GmNOD100在大豆结瘤中起重要作用。hsp17.9 _由于缺乏与结核的相互作用，株系显示出蔗糖合酶活性显着降低，UDP-葡萄糖和乙酰辅酶A（乙酰辅酶A）含量降低，以及在结节三羧酸（TCA）循环中琥珀酸脱氢酶（SDH）的活性降低。 GmNOD100。我们的研究结果揭示了 sHSPs 在大豆根瘤发育和固氮中的重要作用和前所未有的分子机制。