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Plant and Cell Physiology Advance Access originally published online on October 22, 2007
Plant and Cell Physiology 2007 48(12):1724-1736; doi:10.1093/pcp/pcm144
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© The Author 2007. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

The Plant Growth-Promoting Fungus Penicillium simplicissimum GP17-2 Induces Resistance in Arabidopsis thaliana by Activation of Multiple Defense Signals

Md. Motaher Hossain1, Farjana Sultana1, Mayumi Kubota2, Hiroyuki Koyama2 and Mitsuro Hyakumachi2,*

1 United Graduate School of Agricultural Sciences, Gifu University, Yanagido 1-1, Gifu, 501-1193 Japan
2 Faculty of Applied Biological Sciences, Gifu University, Yanagido 1-1, Gifu, 501-1193 Japan

*Corresponding author: E-mail, hyakumac{at}cc.gifu-u.ac.jp; Fax, 81-58-293-2847.


  Abstract

Arabidopsis thaliana grown in soil amended with barley grain inocula of Penicillium simplicissimum GP17-2 or receiving root treatment with its culture filtrate (CF) exhibited clear resistance to Pseudomonas syringae pv. tomato DC3000 (Pst). To assess the contribution of different defense pathways, Arabidopsis genotypes implicated in salicylic acid (SA) signaling expressing the NahG transgene or carrying disruption in NPR1 (npr1), jasmonic acid (JA) signaling (jar1) and ethylene (ET) signaling (ein2) were tested. All genotypes screened were protected by GP17-2 or its CF. However, the level of protection was significantly lower in NahG and npr1 plants than it was in similarly treated wild-type plants, indicating that the SA signaling pathway makes a minor contribution to the GP17-2-mediated resistance and is insufficient for a full response. Examination of local and systemic gene expression revealed that GP17-2 and its CF modulate the expression of genes involved in both the SA and JA/ET signaling pathways. Subsequent challenge of GP17-2-colonized plants with Pst was accompanied by direct activation of SA-inducible PR-2 and PR-5 genes as well as potentiated expression of the JA-inducible Vsp gene. In contrast, CF-treated plants infected with Pst exhibited elevated expression of most defense-related genes (PR-1, PR-2, PR-5, PDF1.2 and Hel) studied. Moreover, an initial elevation of SA responses was followed by late induction of JA responses during Pst infection of induced systemic resistance (ISR)-expressing plants. In conclusion, we hypothesize the involvement of multiple defense mechanisms leading to an ISR of Arabidopsis by GP17-2.

Keywords: Barley grain inoculum - Culture filtrate - Ethylene - Jasmonate - Pseudomonas syringae pv. tomato DC3000 - Salicylic acid

Abbreviations: BGI, barley grain inoculum; BTH, benzothiadiazole; CF, culture filtrate; ET, ethylene; ISR, induced systemic resistance; JA, jasmonic acid; PDA, potato dextrose agar; PDB, potato dextrose broth; PGPF, plant growth-promoting fungi; PGPR, plant growth-promoting rhizobacteria; PR, pathogenesis related; Pst, Pseudomonas syringae pv. tomato DC3000; RT–PCR, reverse transcription–PCR; SA, salicylic acid; SAR, systemic acquired resistance.

(Received October 3, 2007; Accepted October 16, 2007)
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