Arbuscular mycorrhizal symbiosis is accompanied by local and systemic alterations in gene expression and an increase in disease resistance in the shoots

Authors

  • Jinyuan Liu,

    1. Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY14853, USA, and
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    • Present address: Department of Plant Pathology, 334 Plant Science Building, Cornell University, Ithaca, NY14853, USA.

  • Ignacio Maldonado-Mendoza,

    1. Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY14853, USA, and
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    • Present address: CIIDIR-IPN Unidad Sinaloa, Blvd. Juan de Dios Bátiz Paredes 250, Guasave, Sinaloa, México, CP 081101.

  • Melina Lopez-Meyer,

    1. Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY14853, USA, and
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    • Present address: CIIDIR-IPN Unidad Sinaloa, Blvd. Juan de Dios Bátiz Paredes 250, Guasave, Sinaloa, México, CP 081101.

  • Foo Cheung,

    1. The Institute for Genomic Research, 9712 Medical Center Drive, Rockville, MD 20850, USA
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  • Christopher D. Town,

    1. The Institute for Genomic Research, 9712 Medical Center Drive, Rockville, MD 20850, USA
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  • Maria J. Harrison

    Corresponding author
    1. Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY14853, USA, and
      (fax +1 607 254 6779; e-mail mjh78@cornell.edu).
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(fax +1 607 254 6779; e-mail mjh78@cornell.edu).

Summary

In natural ecosystems, the roots of many plants exist in association with arbuscular mycorrhizal (AM) fungi, and the resulting symbiosis has profound effects on the plant. The most frequently documented response is an increase in phosphorus nutrition; however, other effects have been noted, including increased resistance to abiotic and biotic stresses. Here we used a 16 000-feature oligonucleotide array and real-time quantitative RT-PCR to explore transcriptional changes triggered in Medicago truncatula roots and shoots as a result of AM symbiosis. By controlling the experimental conditions, phosphorus-related effects were minimized, and both local and systemic transcriptional responses to the AM fungus were revealed. The transcriptional response of the roots and shoots differed in both the magnitude of gene induction and the predicted functional categories of the mycorrhiza-regulated genes. In the roots, genes regulated in response to three different AM fungi were identified, and, through split-root experiments, an additional layer of regulation, in the colonized or non-colonized sections of the mycorrhizal root system, was uncovered. Transcript profiles of the shoots of mycorrhizal plants indicated the systemic induction of many genes predicted to be involved in stress or defense responses, and suggested that mycorrhizal plants might display enhanced disease resistance. Experimental evidence supports this prediction, and mycorrhizal M. truncatula plants showed increased resistance to a virulent bacterial pathogen, Xanthomonas campestris. Thus, the symbiosis is accompanied by a complex pattern of local and systemic changes in gene expression, including the induction of a functional defense response.

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