Open AccessRoles of Agrobacterium tumefaciens RirA in Iron Regulation, Oxidative Stress Response, and Virulence
Author(s) -
Patchara Ngok-ngam,
Nantaporn Ruangkiattikul,
Aekkapol Mahavihakat,
Susan S. Virgem,
Rojana Sukchawalit,
Skorn Mongkolsuk
Publication year - 2009
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.01380-08
Subject(s) - agrobacterium tumefaciens , biology , mutant , menadione , repressor , siderophore , superoxide dismutase , wild type , virulence , microbiology and biotechnology , superoxide , biochemistry , oxidative stress , gene , gene expression , transformation (genetics) , enzyme
The analysis of genetics and physiological functions ofAgrobacterium tumefaciens RirA (rhizobial iron regulator) has shown that it is a transcription regulator and a repressor of iron uptake systems. TherirA mutant strain (NTLrirA) overproduced siderophores and exhibited a highly constitutive expression of genes involved in iron uptake (fhuA ,irp6A , andfbpA ) compared to that of the wild-type strain (NTL4). The deregulation in the iron control of iron uptake in NTLrirA led to iron overload in the cell, which was supported by the observation that the NTLrirA mutant was more sensitive than wild-type NTL4 to an iron-activated antibiotic, streptonigrin. The NTLrirA mutant was more sensitive than the parental strain to oxidants, including hydrogen peroxide, organic hydroperoxide, and a superoxide generator, menadione. However, the addition of an iron chelator, 2,2′-dipyridyl, reversed the mutant hypersensitivity to H2 O2 and organic hydroperoxide, indicating the role of iron in peroxide toxicity. Meanwhile, the reduced level of superoxide dismutase (SodBIII) was partly responsible for the menadione-sensitive phenotype of the NTLrirA mutant. The NTLrirA mutant showed a defect in tumorigenesis on tobacco leaves, which likely resulted from the increased sensitivity of NTLrirA to oxidants and the decreased ability of NTLrirA to induce virulence genes (virB andvirE ). These data demonstrated that RirA is important forA. tumefaciens during plant-pathogen interactions.