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Research for novel symbiotic genes using RNA polymerase sigma factor rpoH mutants of rhizobia.

Research Project

Project/Area Number 15580056
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeSingle-year Grants
Section一般
Research Field Applied microbiology
Research InstitutionTohoku University

Principal Investigator

MITSUI Hisayuki  Tohoku University, Graduate School of Life Sciences, Associate professor, 大学院・生命科学研究科, 助教授 (40261466)

Project Period (FY) 2003 – 2004
Project Status Completed (Fiscal Year 2004)
Budget Amount *help
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2004: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2003: ¥2,100,000 (Direct Cost: ¥2,100,000)
Keywordsrhizobium / sigma factor / nitrogen fixation / transcription / symbiosis / heat shock protein / マメ科 / 相互作用
Research Abstract

Sinorhizobium meliloti is a root-nodulating nitrogen-fixing bacterium. An S.meliloti strain that is mutant for the rpoH_1 gene, which encodes a σ^<32>-like protein, elicits the formation of ineffective nodules on the host plant alfalfa. We characterized the rpoH_1 mutant for phenotypes related to symbiosis. Alfalfa nodules formed by the rpoH_1 mutant exhibited greatly reduced levels of acetylene reduction activity compared to the wild-type nodules. Whereas intracellular colonization by rhizobia was observed in a zone just below the apical meristem, we found ultrastructural abnormality and signs of degeneration of bacteroids within many host cells in the proximally adjacent zone. In the proximal part of the nodule, only a few nodule cells contained bacteroids. In contrast, the rpoH_1 mutant showed normal induction of nitrogen fixation gene expression in microaerobic culture. These results suggest that the rpoH_1 mutation causes early senescence of bacteroids during the endosymbiotic process, but does not affect the invasion process or the synthesis of the nitrogenase machinery. The rpoH_1 mutant exhibited increased sensitivity to various agents and to acid pH, suggesting that RpoH_1 is required to protect the bacterial cell against environmental stresses encountered within the host. Since RpoH_1 was previously reported to be required for the synthesis of some heat shock proteins (Hsps), we examined the transcription of several genes for Hsp homologs. We found that transcription of groESL_5, lon, and clpB after heat shock was RrpoH_1-dependent, and conserved nucleotide sequences were found in the -35 and -10 regions upstream of the transcription start sites of these genes. Although groESL_5 expression is almost completely dependent on RpoH_1, we found that a groESL_5 mutant strain is still capable of normal symbiotic nitrogen fixation on alfalfa.

Report

(3 results)
  • 2004 Annual Research Report   Final Research Report Summary
  • 2003 Annual Research Report
  • Research Products

    (4 results)

All 2004 Other

All Journal Article (3 results) Publications (1 results)

  • [Journal Article] Sinorhizobium meliloti RpoH_1 is required for effective nitrogen-fixing symbiosis with alfalfa2004

    • Author(s)
      三井 久幸
    • Journal Title

      Molecular Genetics and Genomics 271

      Pages: 416-425

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2004 Final Research Report Summary
  • [Journal Article] Sinorhizobium meliloti RpoH_1 is required for effective nitrogen-fixing symbiosis with alfalfa.2004

    • Author(s)
      Mitsui H
    • Journal Title

      Mol Gen Genomics 271

      Pages: 416-425

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2004 Final Research Report Summary
  • [Journal Article] Sinorhizobium meliloti RpoH_1 is required for effective nitrogen-fixing symbiosis with alfalfa.2004

    • Author(s)
      Mitsui et al.
    • Journal Title

      Mol.Gen.Genomics 271

      Pages: 416-425

    • Related Report
      2004 Annual Research Report
  • [Publications] Mitsui et al.: "Sinorhizobium meliloti RpoH_1 is required for effective nitrogen-fixing symbiosis with alfalfa"Molecular Genetics and Genomics. (in press). (2004)

    • Related Report
      2003 Annual Research Report

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Published: 2003-04-01   Modified: 2016-04-21  

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