Kumiko Oka

National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan

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Publications (2)8.44 Total impact

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    ABSTRACT: Nicotiana tabacum (tobacco) cultivars possessing the N resistance gene to Tobacco mosaic virus (TMV) induce a hypersensitive response, which is accompanied by the production of phytohormones such as salicylic acid (SA) and jasmonic acid (JA), to enclose the invaded virus at the initial site of infection, which inhibits viral multiplication and spread. SA functions as a positive regulator of TMV resistance. However, the role of JA in TMV resistance has not been fully elucidated. Exogenously applied methyl jasmonate, a methyl ester of JA, reduced local resistance to TMV and permitted systemic viral movement. Furthermore, in contrast to a previous finding, we demonstrated that silencing of CORONATINE-INSENSITIVE 1 (COI1), a JA receptor, reduced viral accumulation in a tobacco cultivar possessing the N gene, as did that of allene oxide synthase, a JA biosynthetic enzyme. The reduction in viral accumulation in COI1-silenced tobacco plants was correlated with an increase in SA, and lowering SA levels by introducing a SA hydroxylase gene attenuated this reduction. Viral susceptibility did not change in a COI1-silenced tobacco cultivar lacking the N gene. These results suggest that JA signaling is not directly responsible for susceptibility to TMV, but is indirectly responsible for viral resistance through the partial inhibition of SA-mediated resistance conferred by the N gene, and that a balance between endogenous JA and SA levels is important for determining the degree of resistance.
    Plant and Cell Physiology 09/2013; · 4.13 Impact Factor
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    ABSTRACT: Mitogen-activated kinase (MAPK) cascades are universal signal transduction pathways in eukaryotic cells. In tobacco, two MAPKs, wound-induced protein kinase (WIPK) and salicylic acid (SA)-induced protein kinase (SIPK) are activated by biotic and abiotic stresses. Both WIPK and SIPK positively regulate the biosynthesis of jasmonic acid (JA) and/or ethylene (ET), while negatively regulate SA accumulation. We showed previously that recombinant tobacco MAPK phosphatase (NtMKP1) protein dephosphorylates and inactivates SIPK in vitro, and over-expression of NtMKP1 repressed wound-induced activation of both SIPK and WIPK. To elucidate the role of NtMKP1 in response to biotic and abiotic stresses, we generated transgenic tobacco plants in which NtMKP1 expression was suppressed. Suppression of NtMKP1 expression resulted in enhanced activation of WIPK and SIPK and production of both JA and ET upon wounding. Wound-induced expression of JA/ET inducible genes, basic PR-1 and PI-II, was also significantly enhanced in these plants. Furthermore, NtMKP1-suppressed plants exhibited enhanced resistance against a necrotrophic pathogen, Botrytis cinerea, and lepidopteran herbivores, Mamestra brassicae and Spodoptera litura. These results suggest that NtMKP1 negatively regulates wound response and resistance against both necrotrophic pathogens and herbivorous insects through suppression of JA/ET pathways via inactivation of MAPKs.
    Molecular Plant-Microbe Interactions 02/2013; · 4.31 Impact Factor