Search tips
Search criteria

Results 1-11 (11)

Clipboard (0)

Select a Filter Below

Year of Publication
1.  Overexpression of Phosphomimic Mutated OsWRKY53 Leads to Enhanced Blast Resistance in Rice 
PLoS ONE  2014;9(6):e98737.
WRKY transcription factors and mitogen-activated protein kinase (MAPK) cascades have been shown to play pivotal roles in the regulation of plant defense responses. We previously reported that OsWRKY53-overexpressing rice plants showed enhanced resistance to the rice blast fungus. In this study, we identified OsWRKY53 as a substrate of OsMPK3/OsMPK6, components of a fungal PAMP-responsive MAPK cascade in rice, and analyzed the effect of OsWRKY53 phosphorylation on the regulation of basal defense responses to a virulence race of rice blast fungus Magnaporthe oryzae strain Ina86-137. An in vitro phosphorylation assay revealed that the OsMPK3/OsMPK6 activated by OsMKK4 phosphorylated OsWRKY53 recombinant protein at its multiple clustered serine-proline residues (SP cluster). When OsWRKY53 was coexpressed with a constitutively active mutant of OsMKK4 in a transient reporter gene assay, the enhanced transactivation activity of OsWRKY53 was found to be dependent on phosphorylation of the SP cluster. Transgenic rice plants overexpressing a phospho-mimic mutant of OsWRKY53 (OsWRKY53SD) showed further-enhanced disease resistance to the blast fungus compared to native OsWRKY53-overexpressing rice plants, and a substantial number of defense-related genes, including pathogenesis-related protein genes, were more upregulated in the OsWRKY53SD-overexpressing plants compared to the OsWRKY53-overexpressing plants. These results strongly suggest that the OsMKK4-OsMPK3/OsMPK6 cascade regulates transactivation activity of OsWRKY53, and overexpression of the phospho-mimic mutant of OsWRKY53 results in a major change to the rice transcriptome at steady state that leads to activation of a defense response against the blast fungus in rice plants.
PMCID: PMC4043820  PMID: 24892523
2.  Ubiquitin ligase EL5 maintains the viability of root meristems by influencing cytokinin-mediated nitrogen effects in rice 
Journal of Experimental Botany  2014;65(9):2307-2318.
Short statement
A rice ubiquitin ligase plays a role in preventing root meristematic cell death in the nitrogen-triggered pathway that leads to the production of cytokinin and superoxide.
Root formation is dependent on meristematic activity and is influenced by nitrogen supply. We have previously shown that ubiquitin ligase, EL5, in rice (Oryza sativa) is involved in the maintenance of root meristematic viability. When mutant EL5 protein is overexpressed to dominantly inhibit the endogenous EL5 function in rice, primordial and meristematic necrosis ia observed. Here, we analysed the cause of root cell death in transgenic rice plants (mEL5) overexpressing EL5V162A, which encodes a partly inactive ubiquitin ligase. The mEL5 mutants showed increased sensitivity to nitrogen that was reflected in the inhibition of root formation. Treatment of mEL5 with nitrate or nitrite caused meristematic cell death accompanied by browning. Transcriptome profiling of whole roots exhibited overlaps between nitrite-responsive genes in non-transgenic (NT) rice plants and genes with altered basal expression levels in mEL5. Phytohormone profiling of whole roots revealed that nitrite treatment increased cytokinin levels, but mEL5 constitutively contained more cytokinin than NT plants and showed increased sensitivity to exogenous cytokinin. More superoxide was detected in mEL5 roots after treatment with nitrite or cytokinin, and treatment with an inhibitor of superoxide production prevented mEL5 roots from both nitrite- and cytokinin-induced meristematic cell death. These results indicate a nitrogen-triggered pathway that leads to changes in root formation through the production of cytokinin and superoxide, on which EL5 acts to prevent meristematic cell death.
PMCID: PMC4036501  PMID: 24663342
Cytokinin; nitrogen; reactive oxygen species; rice; root cell death; ubiquitin ligase.
3.  Nationwide Surveillance of Macrolide-Resistant Mycoplasma pneumoniae Infection in Pediatric Patients 
We conducted nationwide surveillance to investigate regional differences in macrolide-resistant (MR) Mycoplasma pneumoniae strains in Japan. The prevalence of MR M. pneumoniae in pediatric patients gradually increased between 2008 and 2012. Although regional differences were observed, high levels of MR genes were detected in all seven surveillance areas throughout Japan and ranged in prevalence from 50% to 93%. These regional differences were closely related to the previous administration of macrolides.
PMCID: PMC3719750  PMID: 23716043
4.  Therapeutic Efficacy of Macrolides, Minocycline, and Tosufloxacin against Macrolide-Resistant Mycoplasma pneumoniae Pneumonia in Pediatric Patients 
The importance of macrolide-resistant (MR) Mycoplasma pneumoniae has become much more apparent in the past decade. We investigated differences in the therapeutic efficacies of macrolides, minocycline, and tosufloxacin against MR M. pneumoniae. A total of 188 children with M. pneumoniae pneumonia confirmed by culture and PCR were analyzed. Of these, 150 patients had a strain with an MR gene and 134 had one with an A-to-G mutation at position 2063 of M. pneumoniae 23S rRNA domain V. Azithromycin (n = 27), clarithromycin (n = 23), tosufloxacin (n = 62), or minocycline (n = 38) was used for definitive treatment of patients with MR M. pneumoniae. Defervescence within 48 h after the initiation of antibiotic therapy was observed in 41% of the patients in the azithromycin group, 48% of those in the clarithromycin group, 69% of those in the tosufloxacin group, and 87% of those in the minocycline group. The average number of days of fever after the administration of antibiotic treatment was lower in the minocycline and tosufloxacin groups than in the macrolide groups. The decrease in the M. pneumoniae burden, as estimated by the number of DNA copies, after 48 to 96 h of treatment was more rapid in patients receiving minocycline (P = 0.016) than in those receiving tosufloxacin (P = 0.049), azithromycin (P = 0.273), or clarithromycin (P = 0.107). We found that the clinical and bacteriological efficacies of macrolides against MR M. pneumoniae pneumonia was low. Our results indicated that minocycline rather than tosufloxacin can be considered the first-choice drug for the treatment of M. pneumoniae pneumonia in children aged ≥8 years.
PMCID: PMC3632908  PMID: 23459497
5.  WRKY76 is a rice transcriptional repressor playing opposite roles in blast disease resistance and cold stress tolerance 
Journal of Experimental Botany  2013;64(16):5085-5097.
OsWRKY76 encodes a group IIa WRKY transcription factor of rice. The expression of OsWRKY76 was induced within 48h after inoculation with rice blast fungus (Magnaporthe oryzae), and by wounding, low temperature, benzothiadiazole, and abscisic acid. Green fluorescent protein-fused OsWRKY76 localized to the nuclei in rice epidermal cells. OsWRKY76 showed sequence-specific DNA binding to the W-box element in vitro and exhibited W-box-mediated transcriptional repressor activity in cultured rice cells. Overexpression of OsWRKY76 in rice plants resulted in drastically increased susceptibility to M. oryzae, but improved tolerance to cold stress. Microarray analysis revealed that overexpression of OsWRKY76 suppresses the induction of a specific set of PR genes and of genes involved in phytoalexin synthesis after inoculation with blast fungus, consistent with the observation that the levels of phytoalexins in the transgenic rice plants remained significantly lower than those in non-transformed control plants. Furthermore, overexpression of OsWRKY76 led to the increased expression of abiotic stress-associated genes such as peroxidase and lipid metabolism genes. These results strongly suggest that OsWRKY76 plays dual and opposing roles in blast disease resistance and cold tolerance.
PMCID: PMC3830488  PMID: 24043853
Blast disease resistance; cold stress; phytoalexin; rice; transcriptional repressor; WRKY.
6.  The rare sugar d-allose acts as a triggering molecule of rice defence via ROS generation 
Journal of Experimental Botany  2013;64(16):4939-4951.
Only d-allose, among various rare monosaccharides tested, induced resistance to Xanthomonas oryzae pv. oryzae in susceptible rice leaves with defence responses: reactive oxygen species, lesion mimic formation, and PR-protein gene expression. These responses were suppressed by ascorbic acid or diphenylene iodonium. Transgenic rice plants overexpressing OsrbohC, encoding NADPH oxidase, were enhanced in sensitivity to d-allose. d-Allose-mediated defence responses were suppressed by the presence of a hexokinase inhibitor. 6-Deoxy-d-allose, a structural derivative of d-allose unable to be phosphorylated, did not confer resistance. Transgenic rice plants expressing Escherichia coli AlsK encoding d-allose kinase to increase d-allose 6-phosphate synthesis were more sensitive to d-allose, but E. coli AlsI encoding d-allose 6-phosphate isomerase expression to decrease d-allose 6-phosphate reduced sensitivity. A d-glucose 6-phosphate dehydrogenase-defective mutant was also less sensitive, and OsG6PDH1 complementation restored full sensitivity. These results reveal that a monosaccharide, d-allose, induces rice resistance to X. oryzae pv. oryzae by activating NADPH oxidase through the activity of d-glucose 6-phosphate dehydrogenase, initiated by hexokinase-mediated conversion of d-allose to d-allose 6-phosphate, and treatment with d-allose might prove to be useful for reducing disease development in rice.
PMCID: PMC3830479  PMID: 24014866
d-Allose; d-glucose 6-phosphate dehydrogenase; hexokinase; NADPH oxidase; Oryza sativa L; rare sugar.
7.  Surface α-1,3-Glucan Facilitates Fungal Stealth Infection by Interfering with Innate Immunity in Plants 
PLoS Pathogens  2012;8(8):e1002882.
Plants evoke innate immunity against microbial challenges upon recognition of pathogen-associated molecular patterns (PAMPs), such as fungal cell wall chitin. Nevertheless, pathogens may circumvent the host PAMP-triggered immunity. We previously reported that the ascomycete Magnaporthe oryzae, a famine-causing rice pathogen, masks cell wall surfaces with α-1,3-glucan during invasion. Here, we show that the surface α-1,3-glucan is indispensable for the successful infection of the fungus by interfering with the plant's defense mechanisms. The α-1,3-glucan synthase gene MgAGS1 was not essential for infectious structure development but was required for infection in M. oryzae. Lack or degradation of surface α-1,3-glucan increased fungal susceptibility towards chitinase, suggesting the protective role of α-1,3-glucan against plants' antifungal enzymes during infection. Furthermore, rice plants secreting bacterial α-1,3-glucanase (AGL-rice) showed strong resistance not only to M. oryzae but also to the phylogenetically distant ascomycete Cochlioborus miyabeanus and the polyphagous basidiomycete Rhizoctonia solani; the histocytochemical analysis of the latter two revealed that α-1,3-glucan also concealed cell wall chitin in an infection-specific manner. Treatment with α-1,3-glucanase in vitro caused fragmentation of infectious hyphae in R. solani but not in M. oryzae or C. miyabeanus, indicating that α-1,3-glucan is also involved in maintaining infectious structures in some fungi. Importantly, rapid defense responses were evoked (a few hours after inoculation) in the AGL-rice inoculated with M. oryzae, C. miyabeanus and R. solani as well as in non-transgenic rice inoculated with the ags1 mutant. Taken together, our results suggest that α-1,3-glucan protected the fungal cell wall from degradative enzymes secreted by plants even from the pre-penetration stage and interfered with the release of PAMPs to delay innate immune defense responses. Because α-1,3-glucan is nondegradable in plants, it is reasonable that many fungal plant pathogens utilize α-1,3-glucan in the innate immune evasion mechanism and some in maintaining the structures.
Author Summary
Magnaporthe oryzae, Cochlioborus miyabeanus, and Rhizoctonia solani are the top three fungal pathogens that are responsible for devastating damage to the production of rice, a staple cereal for half of the world's population. These fungal pathogens infect host plants despite the plants' innate immunity, which is activated upon recognition of a conserved cell wall component in fungi, such as chitin. Fungal pathogens seem to have evading mechanism(s) against the host innate immunity; however, the mechanisms are still unclear. In this study, we discovered a novel mechanism that is commonly used by fungal pathogens to prevent host innate immunity. In this mechanism, fungal pathogens mask the cell wall surfaces with α-1,3-glucan, a polysaccharide that plants cannot degrade. In fact, a transgenic rice secreting a bacterial α-1,3-glucanase, which is able to remove α-1,3-glucan on the fungal surfaces, obtained strong resistance to all of those fungal pathogens. We also showed that plants rapidly activated defense responses against fungi (even before the fungal penetration) when α-1,3-glucan on the fungal surfaces were damaged or removed. Our study suggests that fungal surface α-1,3-glucan interferes with host immunity in many fungal pathogens and that α-1,3-glucan is a potential target for controlling various fungal diseases in plants.
PMCID: PMC3426526  PMID: 22927818
8.  Enhancement of MAMP signaling by chimeric receptors improves disease resistance in plants 
Plant Signaling & Behavior  2011;6(3):449-451.
Plants activate defense responses through the recognition of microbe-associated molecular patterns (MAMPs). Recently, several pattern-recognition receptors (PRRs) have been identified in plants, paving the way for manipulating MAMP signaling. CEBiP is a receptor for the chitin elicitor (CE) identified in the rice plasma membrane and XA21 is a member of the receptor-like protein kinase (RLK) family that confers disease resistance to rice bacterial leaf blight expressing the sulfated protein Ax21. To improve resistance to rice blast, the most serious fungal disease of rice, we aimed to create a defense system that combines high affinity of CEBiP for CE and the ability of XA21 to confer disease resistance. Cultured rice cells expressing the chimeric receptor CRXA, which consists of CEBiP and the intracellular region of XA21, induced cell death accompanied by an increased production of reactive oxygen and nitrogen species after exposure to CE. Rice plants expressing the chimeric receptor exhibited more resistance to rice blast. Engineering PRRs may be a new strategy in molecular breeding for achieving disease resistance.
PMCID: PMC3142436  PMID: 21364321
chimeric receptor; chitin signal; disease resistance; HR cell death; MAMP-induced resistance; rice blast fungus
9.  HvCEBiP, a gene homologous to rice chitin receptor CEBiP, contributes to basal resistance of barley to Magnaporthe oryzae 
BMC Plant Biology  2010;10:288.
Rice CEBiP recognizes chitin oligosaccharides on the fungal cell surface or released into the plant apoplast, leading to the expression of plant disease resistance against fungal infection. However, it has not yet been reported whether CEBiP is actually required for restricting the growth of fungal pathogens. Here we evaluated the involvement of a putative chitin receptor gene in the basal resistance of barley to the ssd1 mutant of Magnaporthe oryzae, which induces multiple host defense responses.
The mossd1 mutant showed attenuated pathogenicity on barley and appressorial penetration was restricted by the formation of callose papillae at attempted entry sites. When conidial suspensions of mossd1 mutant were spotted onto the leaves of HvCEBiP-silenced plants, small brown necrotic flecks or blast lesions were produced but these lesions did not expand beyond the inoculation site. Wild-type M. oryzae also produced slightly more severe symptoms on the leaves of HvCEBiP-silenced plants. Cytological observation revealed that these lesions resulted from appressorium-mediated penetration into plant epidermal cells.
These results suggest that HvCEBiP is involved in basal resistance against appressorium-mediated infection and that basal resistance might be triggered by the recognition of chitin oligosaccharides derived from M. oryzae.
PMCID: PMC3020183  PMID: 21190588
10.  EL5 is involved in root development as an anti-cell death ubiquitin ligase 
Plant Signaling & Behavior  2008;3(2):148-150.
Ubiquitin ligase (E3) plays a central role in substrate recognition during ubiquitination, a post-translational modification of proteins. Rice EL5 is an E3 with a RING-H2 finger domain (RFD) and its transcript is upregulated by a chitin elicitor. The EL5-RFD has been intensively studied and demonstrated to exhibit E3 activity. Its three-dimensional structure was determined for the first time in plant E3, and the amino acid residues required for the interaction with the ubiquitin-conjugating enzyme (E2) were identified. Recent analyses revealed that EL5 plays a crucial role as an E3 in the maintenance of cell viability during root development in rice. In this addendum, we report that the EL5-RFD catalyzes polyubiquitination via the Lys48 residue of ubiquitin. We also discuss the possible role of EL5 as an anti-cell death enzyme. We hypothesize that EL5 might be responsible for mediating the degradation of cytotoxic proteins produced in root cells after the actions of phytohormones.
PMCID: PMC2634009  PMID: 19704739
EL5; E3; RFD; polyubiquitination; RAM; cell death
11.  Two LysM receptor molecules, CEBiP and OsCERK1, cooperatively regulate chitin elicitor signaling in rice 
The Plant Journal  2010;64(2):204-214.
Chitin is a major molecular pattern for various fungi, and its fragments, chitin oligosaccharides, are known to induce various defense responses in plant cells. A plasma membrane glycoprotein, CEBiP (chitin elicitor binding protein) and a receptor kinase, CERK1 (chitin elicitor receptor kinase) (also known as LysM-RLK1), were identified as critical components for chitin signaling in rice and Arabidopsis, respectively. However, it is not known whether each plant species requires both of these two types of molecules for chitin signaling, nor the relationships between these molecules in membrane signaling. We report here that rice cells require a LysM receptor-like kinase, OsCERK1, in addition to CEBiP, for chitin signaling. Knockdown of OsCERK1 resulted in marked suppression of the defense responses induced by chitin oligosaccharides, indicating that OsCERK1 is essential for chitin signaling in rice. The results of a yeast two-hybrid assay indicated that both CEBiP and OsCERK1 have the potential to form hetero- or homo-oligomers. Immunoprecipitation using a membrane preparation from rice cells treated with chitin oligosaccharides suggested the ligand-induced formation of a receptor complex containing both CEBiP and OsCERK1. Blue native PAGE and chemical cross-linking experiments also suggested that a major portion of CEBiP exists as homo-oligomers even in the absence of chitin oligosaccharides.
PMCID: PMC2996852  PMID: 21070404
chitin elicitor; LysM receptor; receptor-like kinase; receptor complex; signal transduction; rice

Results 1-11 (11)