FUNGAL DISEASES Systemic resistance to bacterial leaf speck pathogen in Arabidopsis thaliana induced by the culture filtrate of a plant growth- promoting fungus (PGPF) Phoma sp. GS8-1 Md. Motaher Hossain Æ Farjana Sultana Æ Mayumi Kubota Æ Hiroyuki Koyama Æ Mitsuro Hyakumachi Received: 3 September 2007 / Accepted: 17 December 2007 / Published online: 17 May 2008 Ó The Phytopathological Society of Japan and Springer 2008 Abstract The culture filtrate (CF) from the plant growth- promoting fungus Phoma sp. GS8-1 was found to induce systemic resistance in Arabidopsis thaliana against the bacterial leaf speck pathogen Pseudomonas syringae pv. tomato DC3000 (Pst), and the underlying mechanism was studied. Roots of A. thaliana were treated with CF from GS8-1, and plants expressed a clear resistance to sub- sequent Pst infection; disease severity was reduced, and proliferation of pathogen was suppressed. Various mutants of A. thaliana were used to test whether the CF induced resistance through one of the known signaling pathways: salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). The CF was fully protective against Pst in Arabidopsis mutants jar1 and ein2 similar to wild-type plants. How- ever, its efficacy was reduced in plants containing transgene NahG. Examination of systemic gene expression revealed that CF modulates the expression of SA-inducible PR-1, PR-2 and PR-5 genes, the JA/ET-inducible ChitB gene, and the ET-inducible Hel gene. Moreover, the expression of these genes was further enhanced upon subsequent stimulation after attack by Pst. Our data suggest that in addition to a partial requirement for SA, the signals JA and ET may also play a role in defense signaling in Arabidopsis. Keywords Plant growth-promoting fungi Á Phoma sp. Á Arabidopsis thaliana Á Induced systemic resistance Á Signaling pathways Á Defense-related genes Introduction Fungal isolates collected from the rhizosphere of zoysia- grass (Zoysia tenuifolia) enhance the growth of a variety of crop plants and thus are known as plant growth- promoting fungi (PGPF) (Hyakumachi 1994). PGPF belong to the genera Fusarium, Penicillium, Phoma, Trichoderma, and various sterile fungi. Several PGPF species were reported to suppress diseases caused by soilborne pathogens (Hyakumachi 1994; Shivanna et al. 1996) and to induce a systemic resistance in addition to promoting growth (Meera et al. 1994; Shoresh et al. 2005). Although induced systemic resistance (ISR) is often associated with host resistance induced by rhizo- sphere colonization, elicitors based on metabolites from these non-pathogenic microorganisms have been identified as activators of host resistance in many different plant species. Infiltration of Penicillium janczewskii and its culture filtrate (CF) into melon and cotton leaves induced a systemic resistance and protected the lower part of the melon stem against Rhizoctonia solani, leading to as much as a 100% reduction in the incidence of damping off (Madi and Katan 1998). Previous research also dem- onstrated that living Phoma sp. and their CFs are able to elicit systemic resistance against anthracnose in cucumber (Meera et al. 1994, 1995; Koike et al. 2001), indicating that factors other than root colonization ability, such as chemical substances produced by the mycelia, might be responsible for induction. Induction of resistance by these elicitors triggers a wide range of responses in plants, such Md. M. Hossain Á F. Sultana United Graduate School of Agricultural Sciences, Gifu University, Gifu, Japan M. Kubota Á H. Koyama Á M. Hyakumachi (&) Faculty of Applied Biological Sciences, Gifu University, Yanagido 1-1, Gifu 501-1193, Japan e-mail: hyakumac@gifu-u.ac.jp 123 J Gen Plant Pathol (2008) 74:213–221 DOI 10.1007/s10327-008-0093-5