Bradyrhizobium diazoefficiens Requires Chemical Chaperones To Cope with Osmotic Stress during Soybean Infection.
Bradyrhizobium diazoefficiens Requires Chemical Chaperones To Cope with Osmotic Stress during Soybean Infection.
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DOI：
10.1128/mbio.00390-21
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发表时间：
2021-03-30
期刊：
影响因子：
6.4
通讯作者：
Fischer HM
中科院分区：
文献类型：
--
作者：
Ledermann R;Emmenegger B;Couzigou JM;Zamboni N;Kiefer P;Vorholt JA;Fischer HM
大豆-慢生根瘤菌共生体系具有重要的农业意义，是研究细菌-植物相互作用的模式系统。虽然详细的分子洞察力是关于相互识别和早期结节器官形成，我们的理解的主机强加的条件和生理感染根瘤菌在过渡期间从自由生活状态在根际内共生类杆菌是目前有限的。根瘤菌与豆科植物共生时，会面临环境的变化，包括养分的可利用性和胁迫暴露。遗传电路允许对这些环境刺激做出反应，以优化从自由生活到共生生活方式的转换过程中的生理适应。大豆固氮根瘤菌（Bradyrhizobium diazoefficiens）高效共生的一个关键调节系统是一般胁迫反应（GSR），它依赖于另一个σ因子σEcfG。然而，共生所需的GSR控制过程尚未确定。在这里，我们证明海藻糖的生物合成受到GSR的控制，并且缺乏相应生物合成基因otsA和/或otsB的突变体在共生和选择的自由生活应激条件下表现出GSR缺陷突变体。海藻糖作为细胞质化学伴侣和应激保护剂的作用可以在otsA或otsB突变体中通过引入异源遗传途径生物合成化学上不相关的相容性溶质甘氨酸甜菜碱和（羟基）四氢嘧啶而在功能上被取代。或者，摄取外源性提供的海藻糖也恢复了otsA突变体对高渗和高离子胁迫的有效共生和耐受性。因此，由GSR控制的生物合成导致的细胞质海藻糖水平升高对B至关重要。重氮素能促进细胞生长，以克服宿主感染早期的不利条件，并确保与根瘤发育同步。
The Bradyrhizobium-soybean symbiosis is of great agricultural significance and serves as a model system for fundamental research in bacterium-plant interactions. While detailed molecular insight is available about mutual recognition and early nodule organogenesis, our understanding of the host-imposed conditions and the physiology of infecting rhizobia during the transition from a free-living state in the rhizosphere to endosymbiotic bacteroids is currently limited. When engaging in symbiosis with legume hosts, rhizobia are confronted with environmental changes, including nutrient availability and stress exposure. Genetic circuits allow responding to these environmental stimuli to optimize physiological adaptations during the switch from the free-living to the symbiotic life style. A pivotal regulatory system of the nitrogen-fixing soybean endosymbiont Bradyrhizobium diazoefficiens for efficient symbiosis is the general stress response (GSR), which relies on the alternative sigma factor σEcfG. However, the GSR-controlled process required for symbiosis has not been identified. Here, we demonstrate that biosynthesis of trehalose is under GSR control, and mutants lacking the respective biosynthetic genes otsA and/or otsB phenocopy GSR-deficient mutants under symbiotic and selected free-living stress conditions. The role of trehalose as a cytoplasmic chemical chaperone and stress protectant can be functionally replaced in an otsA or otsB mutant by introducing heterologous genetic pathways for biosynthesis of the chemically unrelated compatible solutes glycine betaine and (hydroxy)ectoine. Alternatively, uptake of exogenously provided trehalose also restores efficient symbiosis and tolerance to hyperosmotic and hyperionic stress of otsA mutants. Hence, elevated cytoplasmic trehalose levels resulting from GSR-controlled biosynthesis are crucial for B. diazoefficiens cells to overcome adverse conditions during early stages of host infection and ensure synchronization with root nodule development.