The ColRS system of Xanthomonas oryzae pv. oryzae is required for virulence and growth in iron-limiting conditions

Authors

  • SUJATHA SUBRAMONI,

    1. Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500 007, Andhra Pradesh, India
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    • Present address: Department of Microbiology and Infectious Diseases, Faculty of Medicine, University of Calgary, 3330 Hospital NW, Calgary, AB, Canada, T2N 4N1

    • These authors contributed equally to this work.

  • ALOK PANDEY,

    1. Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500 007, Andhra Pradesh, India
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    • These authors contributed equally to this work.

  • M. R. VISHNU PRIYA,

    1. Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500 007, Andhra Pradesh, India
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    • These authors contributed equally to this work.

  • HITENDRA KUMAR PATEL,

    1. Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500 007, Andhra Pradesh, India
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  • RAMESH V. SONTI

    Corresponding author
    1. Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500 007, Andhra Pradesh, India
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: Email: sonti@ccmb.res.in

SUMMARY

Xanthomonas oryzae pv. oryzae, the causal agent of bacterial blight of rice, produces siderophores only under iron-limiting conditions. We screened 15 400 mTn5-induced mutants of X. oryzae pv. oryzae and isolated 27 mutants that produced siderophores even under iron-replete conditions. We found that the mTn5 insertions in 25 of these mutants were in or close to six genes. Mutants with insertions in five of these genes [colS, XOO1806 (a conserved hypothetical protein), acnB, prpR and prpB] exhibited a deficiency for growth on iron-limiting medium and a decrease in virulence. Insertions in a sixth gene, XOO0007 (a conserved hypothetical protein), were found to affect the ability to grow on iron-limiting medium, but did not affect the virulence. Targeted gene disruptants for colR (encoding the predicted cognate regulatory protein for ColS) also exhibited a deficiency for growth on iron-limiting medium and a decrease in virulence. colR and colS mutants were defective in the elicitation of hypersensitive response symptoms on the nonhost tomato. In addition, colR and colS mutants induced a rice basal defence response, suggesting that they are compromised in the suppression of host innate immunity. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that a functional ColRS system is required for the optimal expression of several genes encoding components of the type 3 secretion system (T3SS) of X. oryzae pv. oryzae. Our results demonstrate the role of several novel genes, including colR/colS, in the promotion of growth on iron-limiting medium and the virulence of X. oryzae pv. oryzae.

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