Shanghai Key Laboratory of Bio-energy Crops, School of Life Sciences, Shanghai University, Shanghai, 200444, China.
Environ Microbiol Rep. 2022 Aug;14(4):595-603. doi: 10.1111/1758-2229.13079. Epub 2022 May 4.
Sinorhizobium meliloti infects the host plant alfalfa to induce formation of nitrogen-fixation root nodules, which inevitably elicit reactive oxygen species (ROS) bursts and organic peroxide generation. The MarR family regulator OhrR regulates the expression of chloroperoxidase and organic hydrogen resistance protein, which scavenge organic peroxides in free-living S. meliloti cells. The single mutant of ohrR genes SMc01945 (ohrR1) and SMc00098 (ohrR2) lacked symbiotic phenotypes. In this work, we identified the novel ohrR gene SMa2020 (ohrR3) and determined that ohrR genes are important for rhizobial infection, nodulation and nitrogen fixation with alfalfa. By analysing the phenotypes of the single, double and triple deletion mutants of ohrR genes, we demonstrate that ohrR1 and ohrR3 slightly affect rhizobial growth, but ohrR2 and ohrR3 influence cellular resistance to the organic peroxide, tert-butyl hydroperoxide. Deletion of ohrR1 and ohrR3 negatively affected infection thread formation and nodulation, and consequently, plant growth. Correspondingly, the expression of the ROS detoxification genes katA and sodB as well as that of the nitrogenase gene nifH was downregulated in bacteroids of the double and triple deletion mutants, which may underlie the symbiotic defects of these mutants. These findings demonstrate that OhrR proteins play a role in the S. meliloti-alfalfa symbiosis.
根瘤农杆菌感染宿主植物紫花苜蓿诱导形成固氮根瘤，这不可避免地会引发活性氧（ROS）爆发和过氧化物的产生。MarR 家族调控因子 OhrR 调控氯过氧化物酶和有机氢抗性蛋白的表达，这些酶可以清除自由生活的根瘤农杆菌细胞中的过氧化物。ohrR 基因的单突变体 SMc01945（ohrR1）和 SMc00098（ohrR2）缺乏共生表型。在这项工作中，我们鉴定了新的 ohrR 基因 SMa2020（ohrR3），并确定 ohrR 基因对于根瘤农杆菌与紫花苜蓿的感染、结瘤和固氮非常重要。通过分析 ohrR 基因的单、双和三缺失突变体的表型，我们证明 ohrR1 和 ohrR3 对根瘤农杆菌的生长略有影响，但 ohrR2 和 ohrR3 影响细胞对过氧化物叔丁基过氧化氢的抗性。ohrR1 和 ohrR3 的缺失会影响侵染线的形成和结瘤，从而影响植物的生长。相应地，双突变体和三突变体中 ROS 解毒基因 katA 和 sodB 以及固氮基因 nifH 的表达下调，这可能是这些突变体共生缺陷的基础。这些发现表明 OhrR 蛋白在根瘤农杆菌-紫花苜蓿共生中发挥作用。
