Interaction of EXA1 and eIF4E Family Members Facilitates Potexvirus Infection in Arabidopsis thaliana.

Plant viruses depend on a number of host factors for successful infection. Deficiency of critical host factors confers recessively inherited viral resistance in plants. For example, loss of Essential for poteXvirus Accumulation 1 (EXA1) in Arabidopsis thaliana confers resistance to potexviruses. However, the molecular mechanism of how EXA1 assists potexvirus infection remains largely unknown. Previous studies reported that the salicylic acid (SA) pathway is upregulated in exa1 mutants, and EXA1 modulates hypersensitive response-related cell death during EDS1-dependent effector-triggered immunity. Here, we show that exa1-mediated viral resistance is mostly independent of SA and EDS1 pathways. We demonstrate that Arabidopsis EXA1 interacts with three members of the eukaryotic translation initiation factor 4E (eIF4E) family, eIF4E1, eIFiso4E, and novel cap-binding protein (nCBP), through the eIF4E-binding motif (4EBM). Expression of EXA1 in exa1 mutants restored infection by the potexvirus Plantago asiatica mosaic virus (PlAMV), but EXA1 with mutations in 4EBM only partially restored infection. In virus inoculation experiments using Arabidopsis knockout mutants, EXA1 promoted PlAMV infection in concert with nCBP, but the functions of eIFiso4E and nCBP in promoting PlAMV infection were redundant. By contrast, the promotion of PlAMV infection by eIF4E1 was, at least partially, EXA1 independent. Taken together, our results imply that the interaction of EXA1-eIF4E family members is essential for efficient PlAMV multiplication, although specific roles of three eIF4E family members in PlAMV infection differ. IMPORTANCE The genus Potexvirus comprises a group of plant RNA viruses, including viruses that cause serious damage to agricultural crops. We previously showed that loss of Essential for poteXvirus Accumulation 1 (EXA1) in Arabidopsis thaliana confers resistance to potexviruses. EXA1 may thus play a critical role in the success of potexvirus infection; hence, elucidation of its mechanism of action is crucial for understanding the infection process of potexviruses and for effective viral control. Previous studies reported that loss of EXA1 enhances plant immune responses, but our results indicate that this is not the primary mechanism of exa1-mediated viral resistance. Here, we show that Arabidopsis EXA1 assists infection by the potexvirus Plantago asiatica mosaic virus (PlAMV) by interacting with the eukaryotic translation initiation factor 4E family. Our results imply that EXA1 contributes to PlAMV multiplication by regulating translation.

Isolation and characterization of Helicobacter suis from human stomach.

Helicobacter suis, a bacterial species naturally hosted by pigs, can colonize the human stomach in the context of gastric diseases such as gastric mucosa-associated lymphoid tissue (MALT) lymphoma. Because H. suis has been successfully isolated from pigs, but not from humans, evidence linking human H. suis infection to gastric diseases has remained incomplete. In this study, we successfully in vitro cultured H. suis directly from human stomachs. Unlike Helicobacter pylori, the viability of H. suis decreases significantly on neutral pH; therefore, we achieved this using a low-pH medium for transport of gastric biopsies. Ultimately, we isolated H. suis from three patients with gastric diseases, including gastric MALT lymphoma. Successful eradication of H. suis yielded significant improvements in endoscopic and histopathological findings. Oral infection of mice with H. suis clinical isolates elicited gastric and systemic inflammatory responses; in addition, progression of gastric mucosal metaplasia was observed 4 mo postinfection. Because H. suis could be isolated from the stomachs of infected mice, our findings satisfied Koch's postulates. Although further prospective clinical studies are needed, H. suis, like H. pylori, is likely a gastric pathogen in humans. Furthermore, comparative genomic analysis of H. suis using complete genomes of clinical isolates revealed that the genome of each H. suis isolate contained highly plastic genomic regions encoding putative strain-specific virulence factors, including type IV secretion system-associated genes, and that H. suis isolates from humans and pigs were genetically very similar, suggesting possible pig-to-human transmission.

Helicobacter ailurogastricus in Patient with Multiple Refractory Gastric Ulcers, Japan.

We report the isolation of Helicobacter ailurogastricus, a Helicobacter species that infects cats and dogs, from a person with multiple refractory gastric ulcers. In addition to H. suis, which infects pigs, Helicobacter species that infect cats and dogs should be considered as potential gastric pathogens in humans.

Short-chain fatty acids bind to apoptosis-associated speck-like protein to activate inflammasome complex to prevent Salmonella infection.

Short-chain fatty acids (SCFAs) produced by gastrointestinal microbiota regulate immune responses, but host molecular mechanisms remain unknown. Unbiased screening using SCFA-conjugated affinity nanobeads identified apoptosis-associated speck-like protein (ASC), an adaptor protein of inflammasome complex, as a noncanonical SCFA receptor besides GPRs. SCFAs promoted inflammasome activation in macrophages by binding to its ASC PYRIN domain. Activated inflammasome suppressed survival of Salmonella enterica serovar Typhimurium (S. Typhimurium) in macrophages by pyroptosis and facilitated neutrophil recruitment to promote bacterial elimination and thus inhibit systemic dissemination in the host. Administration of SCFAs or dietary fibers, which are fermented to SCFAs by gut bacteria, significantly prolonged the survival of S. Typhimurium-infected mice through ASC-mediated inflammasome activation. SCFAs penetrated into the inflammatory region of the infected gut mucosa to protect against infection. This study provided evidence that SCFAs suppress Salmonella infection via inflammasome activation, shedding new light on the therapeutic activity of dietary fiber.

Cluster II che genes of Pseudomonas syringae pv. tabaci 6605, orthologs of cluster I in Pseudomonas aeruginosa, are required for chemotaxis and virulence.

Pseudomonas syringae pv. tabaci 6605 (Pta6605) is a causal agent of wildfire disease in host tobacco plants and is highly motile. Pta6605 has multiple clusters of chemotaxis genes including cheA, a gene encoding a histidine kinase, cheY, a gene encoding a response regulator, mcp, a gene for a methyl-accepting chemotaxis protein, as well as flagellar and pili biogenesis genes. However, only two major chemotaxis gene clusters, cluster I and cluster II, possess cheA and cheY. Deletion mutants of cheA or cheY were constructed to evaluate their possible role in Pta6605 chemotaxis and virulence. Motility tests and a chemotaxis assay to known attractant demonstrated that cheA2 and cheY2 mutants were unable to swarm and to perform chemotaxis, whereas cheA1 and cheY1 mutants retained chemotaxis ability almost equal to that of the wild-type (WT) strain. Although WT and cheY1 mutants of Pta6605 caused severe disease symptoms on host tobacco leaves, the cheA2 and cheY2 mutants did not, and symptom development with cheA1 depended on the inoculation method. These results indicate that chemotaxis genes located in cluster II are required for optimal chemotaxis and host plant infection by Pta6605 and that cluster I may partially contribute to these phenotypes.

A naturally occurring point mutation in the rocA gene of Streptococcus pyogenes confers the highly virulent phenotype.

INTRODUCTION: Mucoid (MTB313) and nonmucoid (MTB314) strains of group A streptococcus (GAS) emm (antiphagocytic M protein) type 1 were simultaneously isolated from a single patient suffering from streptococcal meningitis. In a CD46-expressing transgenic (CD46 Tg) mouse model of subcutaneous infection into both hind footpads with MTB313 or MTB314, MTB313 showed considerably higher virulence than MTB314. METHODS: The comparative genomic analysis based on the whole-genome sequencing revealed that MTB313 possessed an amber codon within rocA (sensory transduction protein kinase), but MTB314 did not carry this stop codon. Thereafter, MAT101 was generated from MTB313 by introducing pRocA, which contained the full-length rocA from MTB314, into the cloning plasmid pLZ12-Km2. MAT100 was also generated by introducing pLZ12-Km2 into MTB313. RESULTS: Although MTB313 and MAT100 showed large quantities of cell-associated hyaluronic acid (HA) in the culture pellets, MTB314 and MAT101 showed small quantities of HA production. Finally, higher mortalities were observed in the MTB313- or MAT100-infected CD46 Tg mice than the MTB314- or MAT101-infected CD46 Tg mice. CONCLUSIONS: These data indicate the possibility that a spontaneous point mutation in the rocA gene led to the highly virulent phenotype of M1 GAS.

Isolation of Natural Fungal Pathogens from Marchantia polymorpha Reveals Antagonism between Salicylic Acid and Jasmonate during Liverwort-Fungus Interactions.

The evolution of adaptive interactions with beneficial, neutral and detrimental microbes was one of the key features enabling plant terrestrialization. Extensive studies have revealed conserved and unique molecular mechanisms underlying plant-microbe interactions across different plant species; however, most insights gleaned to date have been limited to seed plants. The liverwort Marchantia polymorpha, a descendant of early diverging land plants, is gaining in popularity as an advantageous model system to understand land plant evolution. However, studying evolutionary molecular plant-microbe interactions in this model is hampered by the small number of pathogens known to infect M. polymorpha. Here, we describe four pathogenic fungal strains, Irpex lacteus Marchantia-infectious (MI)1, Phaeophlebiopsis peniophoroides MI2, Bjerkandera adusta MI3 and B. adusta MI4, isolated from diseased M. polymorpha. We demonstrate that salicylic acid (SA) treatment of M. polymorpha promotes infection of the I. lacteus MI1 that is likely to adopt a necrotrophic lifestyle, while this effect is suppressed by co-treatment with the bioactive jasmonate in M. polymorpha, dinor-cis-12-oxo-phytodienoic acid (dn-OPDA), suggesting that antagonistic interactions between SA and oxylipin pathways during plant-fungus interactions are ancient and were established already in liverworts.

The Arabidopsis CERK1-associated kinase PBL27 connects chitin perception to MAPK activation.

Perception of microbe-associated molecular patterns by host cell surface pattern recognition receptors (PRRs) triggers the intracellular activation of mitogen-activated protein kinase (MAPK) cascades. However, it is not known how PRRs transmit immune signals to MAPK cascades in plants. Here, we identify a complete phospho-signaling transduction pathway from PRR-mediated pathogen recognition to MAPK activation in plants. We found that the receptor-like cytoplasmic kinase PBL27 connects the chitin receptor complex CERK1-LYK5 and a MAPK cascade. PBL27 interacts with both CERK1 and the MAPK kinase kinase MAPKKK5 at the plasma membrane. Knockout mutants of MAPKKK5 compromise chitin-induced MAPK activation and disease resistance to Alternaria brassicicola PBL27 phosphorylates MAPKKK5 in vitro, which is enhanced by phosphorylation of PBL27 by CERK1. The chitin perception induces disassociation between PBL27 and MAPKKK5 in vivo Furthermore, genetic evidence suggests that phosphorylation of MAPKKK5 by PBL27 is essential for chitin-induced MAPK activation in plants. These data indicate that PBL27 is the MAPKKK kinase that provides the missing link between the cell surface chitin receptor and the intracellular MAPK cascade in plants.

PCR analysis and specific immunohistochemistry revealing a high prevalence of non-Helicobacter pylori Helicobacters in Helicobacter pylori-negative gastric disease patients in Japan: High susceptibility to an Hp eradication regimen.

BACKGROUND: The clinical significance of non-Helicobacter pylori Helicobacter (NHPH) is still unknown. There are many reports of NHPH-infected patients suffering from gastric diseases. Here, we investigated the polymerase chain reaction (PCR) positivity of NHPH infection in gastric disease patients who were negative for H. pylori (Hp) by the rapid urease test and by pathological observation. MATERIALS AND METHODS: We collected the 296 endoscopically obtained gastric mucosal samples of Hp-negative gastric disease patients diagnosed based on a rapid urease test and pathology from 17 hospitals in Japan from September 2013 to June 2019, and we analyzed the existence of Hp and NHPH by PCR. The samples were also treated by indirect immunohistochemistry using an anti-Helicobacter suis VacA paralog antibody and were observed by confocal laser microscopy. RESULTS: Among the 236 non-Hp-eradicated cases, 49 cases (20.8%) were positive for NHPH. Among them, 20 cases were positive for Helicobacter suis, 7 cases were positive for Helicobacter heilmannii sensu stricto/ Helicobacter ailurogastricus (Hhss/Ha), and the other 22 cases could not be identified. The regional differences in the infection rates were significant. Forty percent of the nodular gastritis cases, 24% of the MALT lymphoma, 17% of the chronic gastritis cases, and 33% of the gastroduodenal ulcer cases were NHPH positive. Forty-five patients had been treated with one of the four types of combinations of a proton pump inhibitor and two antibiotics, and in all of these cases, the NHPH diagnosed by PCR was successfully eradicated. Immunohistochemistry using the Helicobacter suis-specific HsvA antibody coincided well with the PCR results. Among the 29 post-Hp eradication cases, three were NHPH positive, including one Hhss/Ha-positive case. Thus, approx. 20% of the Hp-negative non-Hp-eradicated gastric disease patients treated at 17 hospitals in Japan were infected with NHPH.

The GYF domain protein PSIG1 dampens the induction of cell death during plant-pathogen interactions.

The induction of rapid cell death is an effective strategy for plants to restrict biotrophic and hemi-biotrophic pathogens at the infection site. However, activation of cell death comes at a high cost, as dead cells will no longer be available for defense responses nor general metabolic processes. In addition, necrotrophic pathogens that thrive on dead tissue, take advantage of cell death-triggering mechanisms. Mechanisms by which plants solve this conundrum remain described. Here, we identify PLANT SMY2-TYPE ILE-GYF DOMAIN-CONTAINING PROTEIN 1 (PSIG1) and show that PSIG1 helps to restrict cell death induction during pathogen infection. Inactivation of PSIG1 does not result in spontaneous lesions, and enhanced cell death in psig1 mutants is independent of salicylic acid (SA) biosynthesis or reactive oxygen species (ROS) production. Moreover, PSIG1 interacts with SMG7, which plays a role in nonsense-mediated RNA decay (NMD), and the smg7-4 mutant allele mimics the cell death phenotype of the psig1 mutants. Intriguingly, the psig1 mutants display enhanced susceptibility to the hemi-biotrophic bacterial pathogen. These findings point to the existence and importance of the SA- and ROS-independent cell death constraining mechanism as a part of the plant immune system.

MexEF-OprN multidrug efflux pump transporter negatively controls N-acyl-homoserine lactone accumulation in pseudomonas syringae pv. Tabaci 6605.

Our previous studies revealed that flagellar-motility-defective mutants such as ∆fliC of Pseudomonas syringae pv. tabaci 6605 (Pta6605) have remarkably reduced production of N-acyl-homoserine lactones (AHL), quorum-sensing molecules. To investigate the reason of loss of AHL production in ∆fliC mutant, we carried out transposon mutagenesis. Among approximately 14,000 transconjugants, we found 11 AHL production-recovered (APR) strains. In these APR strains, a transposon was inserted into either mexE or mexF, genes encoding for the multidrug efflux pump transporter MexEF-OprN, and mexT, a gene encoding a putative transcriptional activator for mexEF-oprN. These results suggest that MexEF-OprN is a negative regulator of AHL production. To confirm the negative effect of MexEF-OprN on AHL production, loss- and gain-of-function experiments for mexEF-oprN were carried out. The ∆fliC∆mexF and ∆fliC∆mexT double mutant strains recovered AHL production, whereas the mexT overexpressing strain abolished AHL production, although the psyI, a gene encoding AHL synthase, is transcribed as wild type. Introduction of a mexF or mexT mutation into another flagellar-motility- and AHL production-defective mutant strain, ∆motCD, also recovered the ability to produce AHL. Furthermore, introduction of the mexF mutation into other AHL production-defective mutant strains such as ∆gacA and ∆aefR also recovered AHL production but not to the ∆psyI mutant. These results indicate that MexEF-OprN is a decisive negative determinant of AHL production and accumulation.

Salicylic acid-dependent immunity contributes to resistance against Rhizoctonia solani, a necrotrophic fungal agent of sheath blight, in rice and Brachypodium distachyon.

Rhizoctonia solani is a soil-borne fungus causing sheath blight. In consistent with its necrotrophic life style, no rice cultivars fully resistant to R. solani are known, and agrochemical plant defense activators used for rice blast, which upregulate a phytohormonal salicylic acid (SA)-dependent pathway, are ineffective towards this pathogen. As a result of the unavailability of genetics, the infection process of R. solani remains unclear. We used the model monocotyledonous plants Brachypodium distachyon and rice, and evaluated the effects of phytohormone-induced resistance to R. solani by pharmacological, genetic and microscopic approaches to understand fungal pathogenicity. Pretreatment with SA, but not with plant defense activators used in agriculture, can unexpectedly induce sheath blight resistance in plants. SA treatment inhibits the advancement of R. solani to the point in the infection process in which fungal biomass shows remarkable expansion and specific infection machinery is developed. The involvement of SA in R. solani resistance is demonstrated by SA-deficient NahG transgenic rice and the sheath blight-resistant B. distachyon accessions, Bd3-1 and Gaz-4, which activate SA-dependent signaling on inoculation. Our findings suggest a hemi-biotrophic nature of R. solani, which can be targeted by SA-dependent plant immunity. Furthermore, B. distachyon provides a genetic resource that can confer disease resistance against R. solani to plants.

Flesh-eating Streptococcus pyogenes triggers the expression of receptor activator of nuclear factor-κB ligand.

Human CD46 is a receptor for the M protein of group A streptococcus (GAS). The emm1 GAS strain GAS472 was isolated from a patient suffering from streptococcal toxic shock-like syndrome. Human CD46-expressing transgenic (Tg) mice developed necrotizing fasciitis associated with osteoclast-mediated progressive and severe bone destruction in the hind paws 3 days after subcutaneous infection with 5 × 10(5) colony-forming units of GAS472. GAS472 infection induced expression of the receptor activator of nuclear factor-κB ligand (RANKL) while concomitantly reducing osteoprotegerin expression in the hind limb bones of CD46 Tg mice. Micro-computed tomography analysis of the bones suggested that GAS472 infection induced local bone erosion and systemic bone loss in CD46 Tg mice. Because treatment with monoclonal antibodies (mAbs) against mouse CD4(+) and CD8(+) T lymphocytes did not inhibit osteoclastogenesis, T lymphocyte-derived RANKL was not considered a major contributor to massive bone loss during GAS472 infection. However, immunohistochemical analysis of the hind limb bones showed that GAS472 infection stimulated RANKL production in various bone marrow cells, including fibroblast-like cells. Treatment with a mAb against mouse RANKL significantly inhibited osteoclast formation and bone resorption. These data suggest that increased expression of RANKL in heterogeneous bone marrow cells provoked bone destruction during GAS infection.

Protective efficacy of a hydroxy fatty acid against gastric Helicobacter infections.

BACKGROUND: We have previously revealed that omega-3 polyunsaturated fatty acids can prevent Helicobacter pylori infection by blocking the futalosine pathway, an alternative route for menaquinone (MK) biosynthesis. MATERIALS AND METHODS: 1, Different H. pylori strains were grown in liquid media supplemented with linoleic acid, an omega-6 fatty acid, or its 10-hydroxy derivative, 10-hydroxy-cis-12-octadecenoic acid (HYA), in the presence or absence of MK. The bacterial numbers in the media were estimated by plating; 2, C57BL/6NCrl mice received drinking water supplemented with different fatty acids starting from 1 week before infection with H. pylori or Helicobacter suis until the end of the experiment. The gastric colonization levels of H. pylori or H. suis were determined 2 weeks after infection by plating or quantitative PCR, respectively; 3, Mice were given HYA, starting 1 week before infection with H. suis and continuing until 6 months after infection, for analysis of the gastric conditions. RESULTS: 1, A low concentration (20 µmol/L) of HYA in culture broth suppressed the growth of H. pylori, and this inhibition was reduced by MK supplementation; 2, HYA treatment protected mice against H. pylori or H. suis infection; 3, HYA treatment suppressed the formation of lymphoid follicles in the gastric mucus layer after H. suis infection. CONCLUSIONS: HYA prevents gastric Helicobacter infections by blocking their futalosine pathways. Daily HYA supplementation is effective for the prevention of gastric mucosa-associated lymphoid tissue lymphoma induced by persistent infection with H. suis.

Expression profiling of marker genes responsive to the defence-associated phytohormones salicylic acid, jasmonic acid and ethylene in Brachypodium distachyon.

BACKGROUND: Brachypodium distachyon is a promising model plants for grasses. Infections of Brachypodium by various pathogens that severely impair crop production have been reported, and the species accordingly provides an alternative platform for investigating molecular mechanisms of pathogen virulence and plant disease resistance. To date, we have a broad picture of plant immunity only in Arabidopsis and rice; therefore, Brachypodium may constitute a counterpart that displays the commonality and uniqueness of defence systems among plant species. Phytohormones play key roles in plant biotic stress responses, and hormone-responsive genes are used to qualitatively and quantitatively evaluate disease resistance responses during pathogen infection. For these purposes, defence-related phytohormone marker genes expressed at time points suitable for defence-response monitoring are needed. Information about their expression profiles over time as well as their response specificity is also helpful. However, useful marker genes are still rare in Brachypodium. RESULTS: We selected 34 candidates for Brachypodium marker genes on the basis of protein-sequence similarity to known marker genes used in Arabidopsis and rice. Brachypodium plants were treated with the defence-related phytohormones salicylic acid, jasmonic acid and ethylene, and their transcription levels were measured 24 and 48 h after treatment. Two genes for salicylic acid, 7 for jasmonic acid and 2 for ethylene were significantly induced at either or both time points. We then focused on 11 genes encoding pathogenesis-related (PR) 1 protein and compared their expression patterns with those of Arabidopsis and rice. Phylogenetic analysis suggested that Brachypodium contains several PR1-family genes similar to rice genes. Our expression profiling revealed that regulation patterns of some PR1 genes as well as of markers identified for defence-related phytohormones are closely related to those in rice. CONCLUSION: We propose that the Brachypodium immune hormone marker genes identified in this study will be useful to plant pathologists who use Brachypodium as a model pathosystem, because the timing of their transcriptional activation matches that of the disease resistance response. Our results using Brachypodium also suggest that monocots share a characteristic immune system, defined as the common defence system, that is different from that of dicots.

In the Aftermath of Helicobacter pylori: Other Helicobacters Rising Up to Become the Next Gastric Epidemic?

Non-Helicobacter pylori-Helicobacters including H. suis, H. heilmanniisensu stricto and H. felis comprise a group of bacteria that may inhabit the stomach of humans and animals. Human gastric infection has been associated with gastritis, ulcer, MALT lymphoma and cancer. Although the fastidious nature of these organisms has hampered their research, recent advancements in in vitro cultivation and recent reports on in vivo models and prevalence studies in humans suggest this group of bacteria to be of more clinical significance than earlier believed. The present review discusses their history, microbiology and relevance to human health.

A highly susceptible CD46 transgenic mouse model of subcutaneous infection with Streptococcus dysgalactiae subspecies equisimilis.

The Streptococcus dysgalactiae subspecies equisimilis (SDSE) possesses clinical similarities to group A streptococcus (GAS) and has recently been recognized as a causative pathogen of life-threatening streptococcal infections. Human membrane cofactor protein (CD46), a complement regulatory protein ubiquitously expressed on every cell type except for erythrocytes, has been implicated as a receptor for human-specific pathogens including GAS. In the present report, SDSE strain GGS_124 was isolated from a patient suffering from streptococcal toxic shock syndrome. When CD46-expressing transgenic (Tg) and non-Tg mice were infected subcutaneously into a hind footpad with 1 × 10(7) colony-forming units of GGS_124, both CD46 Tg and non-Tg mice showed similar levels of colonization in the popliteal lymph nodes at day 3 after infection. However, the following differences were found between CD46 Tg and non-Tg mice after infection. First, there was a statistically significant difference in mortality rates between CD46 Tg (33%) and non-Tg (0%) mice within 35 days after infection. Second, all surviving CD46 Tg mice developed ankle arthritis at day 35 after infection, whereas non-Tg mice did not develop ankle arthritis on the infected hind paws. Finally, CD46 Tg mice developed a pus-filled abscess accompanied by renal failure at day 6 or later after infection. These observations suggest that CD46, the host cell-surface pathogen receptor, functioned to attract GGS_124 into deep tissues, so that the subcutaneous infection with GGS_124 induced invasive streptococcal diseases in CD46 Tg mice.

Narrow-spectrum inhibitors targeting an alternative menaquinone biosynthetic pathway of Helicobacter pylori.

We aimed to identify narrow-spectrum natural compounds that specifically inhibit an alternative menaquinone (MK; vitamin K2) biosynthetic pathway (the futalosine pathway) of Helicobacter pylori. Culture broth samples of 6183 microbes were examined using the paper disc method with different combinations of 2 of the following 3 indicator microorganisms: Bacillus halodurans C-125 and Kitasatospora setae KM-6054(T), which have only the futalosine pathway of MK biosynthesis, and Bacillus subtilis H17, which has only the canonical MK biosynthetic pathway. Most of the active compounds isolated from culture broth samples were from the families of polyunsaturated fatty acids (PUFAs). Only one compound isolated from the culture broth of Streptomyces sp. K12-1112, siamycin I (a 21-residue lasso peptide antibiotic), targeted the futalosine pathway. The inhibitory activities of representative PUFAs and siamycin I against the growth of B. halodurans or K. setae were abrogated by supplementation with MK. Thereafter, the growth of H. pylori strains SS1 and TN2GF4 in broth cultures was dose-dependently suppressed by eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), or siamycin I, and these inhibitory effects were reduced by supplementation with MK. Daily administration of EPA (100 µM), DHA (100 µM), or siamycin I (2.5 µM) in drinking water reduced the H. pylori SS1 colonization in the gastric mucosa of C57BL/6 mice by 96%, 78%, and 68%, respectively. These data suggest that EPA, DHA, and siamycin I prevented H. pylori infection by inhibiting the futalosine pathway of MK biosynthesis.

Plasma membrane localization is essential for Oryza sativa Pto-interacting protein 1a-mediated negative regulation of immune signaling in rice.

Oryza sativa Pto-interacting protein 1a (OsPti1a), an ortholog of tomato (Solanum lycopersicum) SlPti1, functions as a negative regulator of innate immunity in rice (Oryza sativa). In ospti1a mutants, the activation of immune responses, including hypersensitive response-like cell death, is caused by loss of the OsPti1a protein; however, it is as yet unclear how OsPti1a suppresses immune responses. Here, we report that OsPti1a localizes to detergent-resistant membrane fractions of the plasma membrane through lipid modification of the protein's amino terminus, which is highly conserved among Pti1 orthologs in several plant species. Importantly, mislocalization of OsPti1a after deletion of its amino terminus reduced its ability to complement the mutant phenotypes, including hypersensitive response-like cell death. Furthermore, complex formation of OsPti1a depends on its amino terminus-mediated membrane localization. Liquid chromatography-tandem mass spectrometry analysis of OsPti1a complex-interacting proteins identified several defense-related proteins. Collectively, these findings indicate that appropriate complex formation by OsPti1a at the plasma membrane is required for the negative regulation of plant immune responses in rice.