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Volume 11
Issue 3
10.3390/genes11030335
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Article

Ohr and OhrR Are Critical for Organic Peroxide Resistance and Symbiosis in Azorhizobium caulinodans ORS571

by
Yang Si
1,
Dongsen Guo
1,
Shuoxue Deng
1,
Xiuming Lu
1,
Juanjuan Zhu
1,
Bei Rao
1,
Yajun Cao
1,
Gaofei Jiang
2,
Daogeng Yu
3,
Zengtao Zhong
1,* and
Jun Zhu
1
1
Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China
2
Jiangsu Provincial Key Lab for Organic Solid Waste Utilization, Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, National Engineering Research Center for Organic-based Fertilizers, Postdoctoral Station of Agricultural Resources and Environment, Nanjing Agricultural University, Nanjing 210095, China
3
Tropical Crops Genetic Resources Institute, Chinese Academy of Tropical Agricultural Science, Danzhou, Hainan 571737, China
*
Author to whom correspondence should be addressed.
Genes 2020, 11(3), 335; https://doi.org/10.3390/genes11030335
Submission received: 23 February 2020 / Revised: 16 March 2020 / Accepted: 20 March 2020 / Published: 20 March 2020
(This article belongs to the Special Issue Genetic Evolution of Root Nodule Symbioses)
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Abstract

Azorhizobium caulinodans is a symbiotic nitrogen-fixing bacterium that forms both root and stem nodules on Sesbania rostrata. During nodule formation, bacteria have to withstand organic peroxides that are produced by plant. Previous studies have elaborated on resistance to these oxygen radicals in several bacteria; however, to the best of our knowledge, none have investigated this process in A. caulinodans. In this study, we identified and characterised the organic hydroperoxide resistance gene ohr (AZC_2977) and its regulator ohrR (AZC_3555) in A. caulinodans ORS571. Hypersensitivity to organic hydroperoxide was observed in an ohr mutant. While using a lacZ-based reporter system, we revealed that OhrR repressed the expression of ohr. Moreover, electrophoretic mobility shift assays demonstrated that OhrR regulated ohr by direct binding to its promoter region. We showed that this binding was prevented by OhrR oxidation under aerobic conditions, which promoted OhrR dimerization and the activation of ohr. Furthermore, we showed that one of the two conserved cysteine residues in OhrR, Cys11, was critical for the sensitivity to organic hydroperoxides. Plant assays revealed that the inactivation of Ohr decreased the number of stem nodules and nitrogenase activity. Our data demonstrated that Ohr and OhrR are required for protecting A. caulinodans from organic hydroperoxide stress and play an important role in the interaction of the bacterium with plants. The results that were obtained in our study suggested that a thiol-based switch in A. caulinodans might sense host organic peroxide signals and enhance symbiosis.
Keywords: Azorhizobium caulinodans; Ohr; OhrR; organic peroxide; symbiosis Azorhizobium caulinodans; Ohr; OhrR; organic peroxide; symbiosis

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MDPI and ACS Style

Si, Y.; Guo, D.; Deng, S.; Lu, X.; Zhu, J.; Rao, B.; Cao, Y.; Jiang, G.; Yu, D.; Zhong, Z.; et al. Ohr and OhrR Are Critical for Organic Peroxide Resistance and Symbiosis in Azorhizobium caulinodans ORS571. Genes 2020, 11, 335. https://doi.org/10.3390/genes11030335

AMA Style

Si Y, Guo D, Deng S, Lu X, Zhu J, Rao B, Cao Y, Jiang G, Yu D, Zhong Z, et al. Ohr and OhrR Are Critical for Organic Peroxide Resistance and Symbiosis in Azorhizobium caulinodans ORS571. Genes. 2020; 11(3):335. https://doi.org/10.3390/genes11030335

Chicago/Turabian Style

Si, Yang, Dongsen Guo, Shuoxue Deng, Xiuming Lu, Juanjuan Zhu, Bei Rao, Yajun Cao, Gaofei Jiang, Daogeng Yu, Zengtao Zhong, and et al. 2020. "Ohr and OhrR Are Critical for Organic Peroxide Resistance and Symbiosis in Azorhizobium caulinodans ORS571" Genes 11, no. 3: 335. https://doi.org/10.3390/genes11030335

APA Style

Si, Y., Guo, D., Deng, S., Lu, X., Zhu, J., Rao, B., Cao, Y., Jiang, G., Yu, D., Zhong, Z., & Zhu, J. (2020). Ohr and OhrR Are Critical for Organic Peroxide Resistance and Symbiosis in Azorhizobium caulinodans ORS571. Genes, 11(3), 335. https://doi.org/10.3390/genes11030335

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