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ABSTRACT: Xanthomonas oryzae pv. oryzae is the causal agent of bacterial blight of rice. The XopR protein, secreted into plant cells through the type III secretion apparatus, is widely conserved in xanthomonads and is predicted to play important roles in bacterial pathogenicity. Here, we examined the function of XopR by constructing transgenic Arabidopsis thaliana plants expressing it under control of the dexamethasone (DEX)-inducible promoter. In the transgenic plants treated with DEX, slightly delayed growth and variegation on leaves were observed. Induction of four microbe-associated molecular pattern (MAMP)-specific early-defense genes by a nonpathogenic X. campestris pv. campestris hrcC deletion mutant were strongly suppressed in the XopR-expressing plants. XopR expression also reduced the deposition of callose, an immune response induced by flg22. When transiently expressed in Nicotiana benthamiana, a XopR::Citrine fusion gene product localized to the plasma membrane. The deletion of XopR in X. oryzae pv. oryzae resulted in reduced pathogenicity on host rice plants. Collectively, these results suggest that XopR inhibits basal defense responses in plants rapidly after MAMP recognition.
Molecular Plant-Microbe Interactions 12/2011; 25(4):505-14. · 4.43 Impact Factor
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Sugihiro Ando,
Yuko Sato,
Hideyuki Shigemori,
Takafumi Shimizu,
Kazunori Okada,
Hisakazu Yamane,
Yusuke Jikumaru,
Yuji Kamiya,
Kosumi Yamada, Chiharu Akimoto-Tomiyama,
Shigeru Tanabe,
Yoko Nishizawa,
Eiichi Minami
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ABSTRACT: We previously detected infection-promoting activity in the supernatant of the conidial suspension (SCS) of the rice blast fungus. In the present study, a molecule carrying the activity was purified and identified as 2'-deoxyuridine (dU). The infection-promoting activity of dU was strictly dependent on its chemical structure and displayed characteristics consistent with those of the SCS. Notably, the activity of dU was exclusively detected during interactions between rice and virulent isolates of the fungus, the number of susceptible lesions in leaf blades was increased by dU, and nonhost resistance in rice plants was not affected by treatment with dU. In addition, the expression of pathogensis-related genes, accumulation of H(2)O(2), and production of phytoalexins in rice in response to inoculation with virulent fungal isolates was not suppressed by dU. The infection-promoting activity of dU was not accompanied by elevated levels of endogenous abscissic acid, which is known to modify plant-pathogen interactions, and was not detected in interactions between oat plants and a virulent oat blast fungus isolate. Taken together, these results demonstrate that dU is a novel infection-promoting factor that acts specifically during compatible interactions between rice plants and rice blast fungus in a mode distinct from that of toxins and suppressors.
Molecular Plant-Microbe Interactions 05/2011; 24(5):519-32. · 4.43 Impact Factor
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ABSTRACT: Many factors produced by the pathogen Magnaporthe oryzae enhance its ability to infect rice. We found a novel infection-promoting activity in the supernatant of a conidia suspension (SCS) of M. oryzae. The addition of SCS promoted the invasion of excised rice leaf sheaths by infectious hyphae. The activity was heat-stable and was found in SCSs from five virulent and three avirulent isolates of M. oryzae on the rice cv. Nipponbare (Pia). The effect was exclusively detected in compatible interactions. The infection of rice plants by non-rice blast fungi was not enhanced by SCS. These results suggest that SCS includes a heat-stable factor(s) that promotes M. oryzae infection during compatible interactions.
Journal of Phytopathology 02/2009; 157(7‐8):420 - 426. · 0.79 Impact Factor
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ABSTRACT: Pseudomonas syringae strains deliver diverse type III effector proteins into host cells, where they can act as virulence factors. Although the functions of the majority of type III effectors are unknown, several have been shown to interfere with plant basal defense mechanisms. Type III effectors also could contribute to bacterial virulence by enhancing nutrient uptake and pathogen adaptation to the environment of the host plant. We demonstrate that the type III effector HopAM1 (formerly known as AvrPpiB) enhances the virulence of a weak pathogen in plants that are grown under drought stress. This is the first report of a type III effector that aids pathogen adaptation to water availability in the host plant. Expression of HopAM1 makes transgenic Ws-0 Arabidopsis hypersensitive to abscisic acid (ABA) for stomatal closure and germination arrest. Conditional expression of HopAM1 in Arabidopsis also suppresses basal defenses. ABA responses overlap with defense responses and ABA has been shown to suppress defense against P. syringae pathogens. We propose that HopAM1 aids P. syringae virulence by manipulation of ABA responses that suppress defense responses. In addition, host ABA responses enhanced by type III delivery of HopAM1 protect developing bacterial colonies inside leaves from osmotic stress.
Molecular Plant-Microbe Interactions 04/2008; 21(3):361-70. · 4.43 Impact Factor
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Tetsuya Chujo,
Tomoaki Kato,
Kazunari Yamada,
Ryota Takai, Chiharu Akimoto-Tomiyama,
Eiichi Minami,
Yoshiaki Nagamura,
Naoto Shibuya,
Michiko Yasuda,
Hideo Nakashita,
Kenji Umemura,
Atsushi Okada,
Kazunori Okada,
Hideaki Nojiri,
Hisakazu Yamane
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ABSTRACT: Expression of OsWRKY71, a rice WRKY gene, was induced by biotic elicitors and pathogen infection. It was also found that OsWRKY71 has features characteristic of a transcriptional repressor. Microarray analysis revealed that several elicitor-induced defense-related genes were upregulated in rice cells overexpressing OsWRKY71. These results indicate that the activation of defense-related genes by OsWRKY71 was probably indirect.
Bioscience Biotechnology and Biochemistry 02/2008; 72(1):240-5. · 1.28 Impact Factor
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ABSTRACT: When various autoclaved microbial cells suspensions (exogenous elicitors) were added to Catharanthus roseus cell cultures, its growth was inhibited but 5'-phosphodiesterase (PDase) production was stimulated. The greatest effect was with autoclaved Alteromonas macleodii: the dry cell concentration decreased from 13 to 10.9 mg/ml while PDase production increased from 0.022 to 0.235 U/ml. A combination of A. macleodii (as exogenous elicitor) and 0.1%(w/v) alginate oligomers (AO: acting as both endogenous elicitor and scavenger of active oxygen species) minimized the cell growth inhibition but enhanced PDase production (0.474 U/ml) about 20 times higher than the control (no addition). The method for the preparation of mixed alginate elicitors with high activities containing exogenous elicitor (autoclaved A. macleodii), endogenous elicitor (AO), and trans-4,5-dihydroxy-2-cyclopenten-1-one was developed. The mixed alginate elicitors significantly promoted PDase production (2.67 U/ml) by C. roseus, and the productivity was increased 120-fold compared to the control without cell growth inhibition.
Biotechnology Letters 11/2006; 28(19):1567-71. · 1.68 Impact Factor
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ABSTRACT: Chitin is a major component of fungal cell walls and serves as a molecular pattern for the recognition of potential pathogens in the innate immune systems of both plants and animals. In plants, chitin oligosaccharides have been known to induce various defense responses in a wide range of plant cells including both monocots and dicots. To clarify the molecular machinery involved in the perception and transduction of chitin oligosaccharide elicitor, a high-affinity binding protein for this elicitor was isolated from the plasma membrane of suspension-cultured rice cells. Characterization of the purified protein, CEBiP, as well as the cloning of the corresponding gene revealed that CEBiP is actually a glycoprotein consisting of 328 amino acid residues and glycan chains. CEBiP was predicted to have a short membrane spanning domain at the C terminus. Knockdown of CEBiP gene by RNA interference resulted in the suppression of the elicitor-induced oxidative burst as well as the gene responses, showing that CEBiP plays a key role in the perception and transduction of chitin oligosaccharide elicitor in the rice cells. Structural analysis of CEBiP also indicated the presence of two LysM motifs in the extracellular portion of CEBiP. As the LysM motif has been known to exist in the putative Nod-factor receptor kinases involved in the symbiotic signaling between leguminous plants and rhizobial bacteria, the result indicates the involvement of partially homologous plasma membrane proteins both in defense and symbiotic signaling in plant cells.
Proceedings of the National Academy of Sciences 08/2006; 103(29):11086-91. · 9.68 Impact Factor
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Chiharu Akimoto-Tomiyama,
Katsumi Sakata,
Junshi Yazaki,
Keiko Nakamura,
Fumiko Fujii,
Kanako Shimbo,
Kimiko Yamamoto,
Takuji Sasaki,
Naoki Kishimoto,
Shoshi Kikuchi,
Naoto Shibuya,
Eiichi Minami
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ABSTRACT: N-acetylchitooligosaccharides are potent elicitors to suspension-cultured rice cells, inducing a set of defense reactions. Expression of defense-related genes is considered to play an important role in defense reactions, and we employed microarray analysis of 8987 randomly selected expressed sequence tags to analyze the changes in gene expression caused by N-acetylchitooctaose. In this experiment, 166 genes were significantly induced and 93 genes were repressed. RNA gel blot analysis of 16 of these genes confirmed the microarray results. Of the 259 ESTs identified as responsive to N-acetylchytooctaose, 18 genes are related to signal transduction, including five calcium-dependent protein kinases (CDPKs). Among these, three novel CDPKs responsive to N-acetylchitooctaose were isolated.
Plant Molecular Biology 07/2003; 52(3):537-51. · 4.15 Impact Factor
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ABSTRACT: Polyalginate was autoclaved at 121 degrees C for 20 min and its molecular weight distribution was analyzed. The autoclaved alginate yielded alginate polymer, oligomer and heat degraded products (HDPs). Each of the separated substances promoted 5'-phosphodiesterase (5'-PDase) production in suspension culture of Catharanthus roseus cells. HDPs could also be generated from other uronic acids (galacturonic acid and glucuronic acid) by autoclave treatment. The most effective substance in the HDPs was isolated and characterized as trans-4,5-dihydroxy-2-cyclopenten-1-one (DHCP). The optimal conditions for DHCP production were also established (autoclaving 1 mg/ml monogalacturonic acid [pH 2] at 121 degrees C for 2 h). A combination of oligo-alginate (below 4 kDa) and HDPs significantly promoted the production of 5'-PDase in C. roseus. Based on the above results, a novel alginate complex that gave a 44-fold increase in 5'-PDase production by C. roseus was developed.
Journal of Bioscience and Bioengineering 02/2002; 94(2):154-9. · 1.79 Impact Factor
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Tetsuya Chujo,
Ryota Takai, Chiharu Akimoto-Tomiyama,
Sugihiro Ando,
Eiichi Minami,
Yoshiaki Nagamura,
Hanae Kaku,
Naoto Shibuya,
Michiko Yasuda,
Hideo Nakashita,
Kenji Umemura,
Atsushi Okada,
Kazunori Okada,
Hideaki Nojiri,
Hisakazu Yamane
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ABSTRACT: We present a detailed characterization of the chitin oligosaccharide elicitor-induced gene OsWRKY53. OsWRKY53 was also induced in suspension-cultured rice cells by a fungal cerebroside elicitor and in rice plants by infection with the blast fungus Magnaporthe grisea. A fusion of OsWRKY53 with green fluorescent protein was detected exclusively in the nuclei of onion epidermal cells, and OsWRKY53 protein specifically bound to W-box elements. A transient assay using the particle bombardment method showed that OsWRKY53 is a transcriptional activator. A microarray analysis revealed that several defense-related genes, including pathogenesis-related protein genes such as PBZ1, were upregulated in rice cells overexpressing OsWRKY53. Finally, overexpression of OsWRKY53 in rice plants resulted in enhanced resistance to M. grisea. These results strongly suggest that OsWRKY53 is a transcription factor that plays important roles in elicitor-induced defense signaling pathways in rice.
Biochimica et Biophysica Acta 1769(7-8):497-505. · 4.66 Impact Factor
