Dual phosphorylation of DGK5-mediated PA burst regulates ROS in plant immunity.

Phosphatidic acid (PA) and reactive oxygen species (ROS) are crucial cellular messengers mediating diverse signaling processes in metazoans and plants. How PA homeostasis is tightly regulated and intertwined with ROS signaling upon immune elicitation remains elusive. We report here that Arabidopsis diacylglycerol kinase 5 (DGK5) regulates plant pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). The pattern recognition receptor (PRR)-associated kinase BIK1 phosphorylates DGK5 at Ser-506, leading to a rapid PA burst and activation of plant immunity, whereas PRR-activated intracellular MPK4 phosphorylates DGK5 at Thr-446, which subsequently suppresses DGK5 activity and PA production, resulting in attenuated plant immunity. PA binds and stabilizes the NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD), regulating ROS production in plant PTI and ETI, and their potentiation. Our data indicate that distinct phosphorylation of DGK5 by PRR-activated BIK1 and MPK4 balances the homeostasis of cellular PA burst that regulates ROS generation in coordinating two branches of plant immunity.

Toxicological effects of tire rubber-derived 6PPD-quinone, a species-specific toxicant, and dithiobisbenzanilide (DTBBA) in the marine rotifer Brachionus koreanus.

The ingredients of tire-rubber products include a complex range of chemicals additives, most of which are leached into surrounding water as unmeasured toxicants with unexplored ecotoxicological impacts. The present study summarizes the reported species-specific acute toxicity of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), the ozonation product of anti-oxidant 6PPD used in tire rubber. Also, chronic toxicity and oxidative response of 6PPD-Q and another tire-rubber derivative, 2',2'''-dithiobisbenzanilide (DTBBA), in rotifer Brachionus koreanus were investigated. Although 6PPD-Q has been reported to be highly toxic to several species of salmonids, only moderate chronic toxicity was observed in B. koreanus. In contrast, DTBBA significantly retarded the population growth and fecundity. The varying toxicity of 6PPD-Q and DTBBA was linked to the level of reactive oxygen species in which DTBBA exposure caused a significant concentration-dependent increase. Our results imply unanticipated risks to aquatic species posed by chemical additives in tire-rubber which may be considered emerging contaminants of toxicological concern.

Environmental DNA surveillance of biocontamination in a drinking water treatment plant.

A clean and adequate supply of drinking water is essential to life and good health. However, despite the risk of biologically derived contamination of drinking water, monitoring of invertebrate outbreaks has relied primarily on naked-eye inspections that are prone to errors. In this study, we applied environmental DNA (eDNA) metabarcoding as a biomonitoring tool at seven different stages of drinking water treatment, from prefiltration to release from household faucets. While the composition of invertebrate eDNA communities reflected the communities of the source water in earlier stages of the treatment, several predominant invertebrate taxa (e.g., rotifer) were shown to be introduced during purification, but most were eliminated in later treatment stages. In addition, the limit of detection/quantification of PCR assay and read capacity of high-throughput sequencing was assessed with further microcosm experiments to estimate the applicability eDNA metabarcoding to the biocontamination surveillance in drinking water treatment plants (DWTPs). Here we propose a novel eDNA-based approach for sensitive and efficient surveillance of invertebrate outbreaks in DWTPs.

Maternal exposure to nanoplastic induces transgenerational toxicity in the offspring of rotifer Brachionus koreanus.

Nanoplastics have received a great deal of attention as evidence of their potential harmful effects on aquatic biota. In zooplankton, ingestion is known as a major uptake route of nanoplastics due to the low feeding selectivity of filter-feeding organisms. In this study, we propose maternal transfer as an alternative uptake route of nanoplastic in the rotifer Brachionus koreanus. Exposure to nanoplastics in parental rotifers induced maternal transfer in offspring, as revealed by fluorescence in rotifer eggs. We further verified that egg shells are not permeable to nanoplastics, and the observed fluorescence was associated with nanoplastic particles, not leached fluorescent dye, supporting the idea that nanoplastics can be transferred through an intrinsic maternal transfer route. This maternal transfer induced adverse effects on life-cycle parameters, including development and reproduction, in offspring rotifers, and was associated with oxidative stress. The results of this study shed light on the ecological impacts of nanoplastics in marine environments.

An unexpected role for tomato threonine deaminase 2 in host defense against bacterial infection.

The hormones salicylic acid (SA) and jasmonic acid (JA) often act antagonistically in controlling plant defense pathways in response to hemibiotrophs/biotrophs (hemi/biotroph) and herbivores/necrotrophs, respectively. Threonine deaminase (TD) converts threonine to α-ketobutyrate and ammonia as the committed step in isoleucine (Ile) biosynthesis and contributes to JA responses by producing the Ile needed to make the bioactive JA-Ile conjugate. Tomato (Solanum lycopersicum) plants have two TD genes: TD1 and TD2. A defensive role for TD2 against herbivores has been characterized in relation to JA-Ile production. However, it remains unknown whether TD2 is also involved in host defense against bacterial hemi/biotrophic and necrotrophic pathogens. Here, we show that in response to the bacterial pathogen-associated molecular pattern (PAMP) flagellin flg22 peptide, an activator of SA-based defense responses, TD2 activity is compromised, possibly through carboxy-terminal cleavage. TD2 knockdown (KD) plants showed increased resistance to the hemibiotrophic bacterial pathogen Pseudomonas syringae but were more susceptible to the necrotrophic fungal pathogen Botrytis cinerea, suggesting TD2 plays opposite roles in response to hemibiotrophic and necrotrophic pathogens. This TD2 KD plant differential response to different pathogens is consistent with SA- and JA-regulated defense gene expression. flg22-treated TD2 KD plants showed high expression levels of SA-responsive genes, whereas TD2 KD plants treated with the fungal PAMP chitin showed low expression levels of JA-responsive genes. This study indicates TD2 acts negatively in defense against hemibiotrophs and positively against necrotrophs and provides insight into a new TD2 function in the elaborate crosstalk between SA and JA signaling induced by pathogen infection.

Overexpression of maize ZmLOX6 in Arabidopsis thaliana enhances damage-induced pentyl leaf volatile emissions that affect plant growth and interaction with aphids.

Pentyl leafy volatiles (PLV) are C5 volatiles produced from polyunsaturated fatty acids by plant 13-lipoxygenases (13-LOX) in concert with other lipid metabolizing enzymes. Unlike related C6 volatiles (GLV, green leafy volatiles), little is known about the biosynthesis and physiological function of PLV in plants. Zea mays LOX6 (ZmLOX6) is an unusual plant LOX that lacks lipid oxygenation activity but acts as a hydroperoxide lyase hypothesized to be specifically involved in PLV synthesis. We overexpressed ZmLOX6 in Arabidopsis thaliana and established that it indeed produces PLVs. Overexpression of ZmLOX6 caused a mild chlorotic phenotype, and induced a similar phenotype in untransformed Col-0 plants grown in close proximity, suggesting that airborne signals, such as PLVs, are responsible for the phenotype. PLV production, dependency on the substrate from endogenous 13-LOX(s), and likely competition with endogenous 13-oxylipin pathway were consistent with the model that ZmLOX6 functions as a hydroperoxide lyase. The abundance of individual PLVs was differentially affected by ZmLOX6 overexpression, and the new profile indicated that ZmLOX6 had reaction products distinct from endogenous PLV-producing activities in the Arabidopsis host plants. ZmLOX6 overexpression also induced a new hormonal status, which is likely responsible for increased attraction and propagation of aphids, nonetheless improving host plant tolerance to aphid infestation.

Phenotypic toxicity, oxidative response, and transcriptomic deregulation of the rotifer Brachionus plicatilis exposed to a toxic cocktail of tire-wear particle leachate.

Tire-wear particles (TWPs) are potential source of microplastic (MP) pollution in marine environments. Although the hazardous effects of MPs on marine biota have received considerable attention, the toxicity of TWPs and associated leachates remain poorly understood. Here, to assess the toxicity of TWP leachate and the underlying mechanisms of toxicity, the phenotypic and transcriptomic responses of the rotifer Brachionus plicatilis were assessed with chemistry analysis of a TWP leachate. Although acute toxicity was induced, and a variety of metals and polyaromatic hydrocarbons were detected in the leachate, levels were below the threshold for acute toxicity. The results of particle analysis suggest that the acute toxicity observed in our study is the result of a toxic cocktail of micro- and/or nano-sized TWPs and other additives in TWP leachate. The adverse effects of TWP leachate were associated with differential expression of genes related to cellular processes, stress response, and impaired metabolism, with further oxidative stress responses. Our results imply that TWPs pose a greater threat to marine biota than other plastic particles as they constitute a major source of nano- and microplastics that have synergistic effects with the additives contained in TWP leachate.

Effects of atrazine and diuron on life parameters, antioxidant response, and multixenobiotic resistance in non-targeted marine zooplankton.

Atrazine and diuron are among the most widely used antifoulant biocides in the world. Due to their persistence in the environment, they can induce adverse effects on non-targeted organisms. In this study, we investigated the chronic in vivo toxicity of atrazine and diuron with further assessments on oxidative stress responses (e.g., oxidative stress, antioxidant) and multixenobiotic resistance (MXR) function in the rotifer Brachionus koreanus, a non-targeted microzooplanktonic grazer at the primary level of the marine food chain. Although similar oxidative response was shown by both biocides, diuron induced stronger retardation on reproduction and population growth rates of B. koreanus while moderate effects were observed by atrazine. This higher toxicity of diuron was shown to be associated with its stronger inhibition of MXR conferred by P-glycoprotein and multidrug resistance proteins which play as a first line of defense by transporting various toxicants out of a cell. Our study provides new insight into non-targeted effects of biocides on marine zooplankton and mechanisms beyond their different degrees of toxicity.

Knowing me, knowing you: Self and non-self recognition in plant immunity.

Perception of non-self molecules known as microbe-associated molecular patterns (MAMPs) by host pattern recognition receptors (PRRs) activates plant pattern-triggered immunity (PTI). Pathogen infections often trigger the release of modified-self molecules, termed damage- or danger-associated molecular patterns (DAMPs), which modulate MAMP-triggered signaling to shape the frontline of plant immune responses against infections. In the context of advances in identifying MAMPs and DAMPs, cognate receptors, and their signaling, here, we focus on the most recent breakthroughs in understanding the perception and role of non-self and modified-self patterns. We highlight the commonalities and differences of MAMPs from diverse microbes, insects, and parasitic plants, as well as the production and perception of DAMPs upon infections. We discuss the interplay between MAMPs and DAMPs for emerging themes of the mutual potentiation and attenuation of PTI signaling upon MAMP and DAMP perception during infections.

Screening for potential nuclear substrates for the plant cell death suppressor kinase Adi3 using peptide microarrays.

The tomato AGC protein kinase Adi3 is a Ser/Thr kinase that functions as a negative regulator of programmed cell death through cell death suppression (CDS) activity in the nucleus. In this study, to understand the mechanism of Adi3 CDS, peptide microarrays containing random Ser- and Thr-peptide phosphorylation substrates were used to screen for downstream phosphorylation substrates. In the microarray phosphorylation assay, Adi3 showed promiscuous kinase activity more toward Ser-peptides compared to Thr-peptides, and a preference for aromatic and cyclic amino acids on both Ser- and Thr-peptides was seen. The 63 highest phosphorylated peptide sequences from the Ser-peptide microarray were selected as queries for a BLAST search against the tomato proteome. As a result, 294 candidate nuclear Adi3 substrates were selected and categorized based on their functions. Many of these proteins were classified as DNA/RNA polymerases or regulators involved in transcription and translation events. The list of potential Adi3 substrates was narrowed to eleven and four candidates were tested for phosphorylation by Adi3. Two of these candidates, RNA polymerase II 2nd largest subunit (RPB2) and the pathogen defense related transcription factor Pti5, were confirmed as Adi3 phosphorylation substrates by in vitro kinase assays. Using a mutational approach two residues, Thr675 and Thr676, were identified as Adi3 phosphorylation sites on RPB2. This study provides the foundation for understanding Adi3 CDS mechanisms in the nucleus as well as other cellular functions.

RNA-Seq Analysis of Antibiotic-Producing Bacillus subtilis SC-8 Reveals a Role for Small Peptides in Controlling PapR Signaling.

Bacillus subtilis SC-8 (BSSC8) shows a narrow antimicrobial activity against the Bacillus cereus group. Previously, B. cereus-derived PapR as a signal peptide to stimulate PlcR, which plays a significant role in regulating the transcription of virulence factors, was assumed to stimulate antibiotic production in BSSC8. To better understand the functional role of PapR in the antibiotic production of BSSC8 and the interspecies interaction, the global transcriptomic profiling of BSSC8 was investigated using RNA-Seq in this study. Small peptides derived from B. cereus wild type (WTBC) and a papR-deleted mutant strain (MTBC) were individually supplied to BSSC8 cultures, and changes in global transcription levels were compared by RNA-Seq. In the presence of WTBC small peptides, more genes (80.9%) were significantly upregulated than in cells exposed to MTBC small peptides. Specifically, 48.8 and 83.4% of genes involved in glycolysis and the TCA cycle, respectively, showed changes in transcription levels in response to small peptides from both strains. Of the genes showing the alterations, 35.0% (glycolysis) and 60.0% (TCA cycle) of transcripts were significantly regulated only in response to WTBC-derived small peptides. Furthermore, the expression of biosynthetic genes encoding several known antibiotics in BSSC8 was further decreased in response to WTBC small peptides.

Antimicrobial peptides of the genus Bacillus: a new era for antibiotics.

The rapid onset of resistance reduces the efficacy of most conventional antimicrobial drugs and is a general cause of concern for human well-being. Thus, there is great demand for a continuous supply of novel antibiotics to combat this problem. Bacteria-derived antimicrobial peptides (AMPs) have long been used as food preservatives; moreover, prior to the development of conventional antibiotics, these AMPs served as an efficient source of antibiotics. Recently, peptides produced by members of the genus Bacillus were shown to have a broad spectrum of antimicrobial activity against pathogenic microbes. Bacillus-derived AMPs can be synthesized both ribosomally and nonribosomally and can be classified according to peptide biosynthesis, structure, and molecular weight. The precise mechanism of action of these AMPs is not yet clear; however, one proposed mechanism is that these AMPs kill bacteria by forming channels in and (or) disrupting the bacterial cell wall. Bacillus-derived AMPs have potential in the pharmaceutical industry, as well as the food and agricultural sectors. Here, we focus on Bacillus-derived AMPs as a novel alternative approach to antibacterial drug development. We also provide an overview of the biosynthesis, mechanisms of action, applications, and effectiveness of different AMPs produced by members of the Bacillus genus, including several recently identified novel AMPs.

Role of an active site loop in the promiscuous activities of Amycolatopsis sp. T-1-60 NSAR/OSBS.

The o-succinylbenzoate synthase (OSBS) family is part of the functionally diverse enolase superfamily. Many proteins in one branch of the OSBS family catalyze both OSBS and N-succinylamino acid racemization in the same active site. In some promiscuous NSAR/OSBS enzymes, NSAR activity is biologically significant in addition to or instead of OSBS activity. Identifying important residues for each reaction could provide insight into how proteins evolve new functions. We have made a series of mutations in Amycolatopsis sp. T-1-60 NSAR/OSBS in an active site loop, referred to as the 20s loop. This loop affects substrate specificity in many members of the enolase superfamily but is poorly conserved within the OSBS family. Deletion of this loop decreased OSBS and NSAR catalytic efficiency by 4500-fold and 25,000-fold, respectively, showing that it is essential. Most point mutations had small effects, changing the efficiency of both NSAR and OSBS activities <10-fold compared to that of the wild type. An exception was F19A, which reduced kcat/KM(OSBS) 200-fold and kcat/KM(NSAR) 120-fold. Mutating the surface residue R20E, which can form a salt bridge to help close the 20s loop over the active site, had a more modest effect, decreasing kcat/KM of OSBS and NSAR reactions 32- and 8-fold, respectively. Several mutations increased KM of the NSAR reaction more than that of the OSBS reaction. Thus, both activities require the 20s loop, but differences in how mutations affect OSBS and NSAR activities suggest that some substitutions in this loop made a small contribution to the evolution of NSAR activity, although additional mutations were probably required.

RNA-seq analysis of antibiotic-producing Bacillus subtilis SC-8 in response to signal peptide PapR of Bacillus cereus.

Bacillus subtilis SC-8 produces an antibiotic that has narrow antagonistic activity against bacteria in the Bacillus cereus group. In B. cereus group bacteria, peptide-activating PlcR (PapR) plays a significant role in regulating the transcription of virulence factors. When B. subtilis SC-8 and B. cereus are co-cultured, PapR is assumed to stimulate antibiotic production by B. subtilis SC-8. To better understand the effect of PapR on this interspecies interaction, the global transcriptome profile of B. subtilis SC-8 was analyzed in the presence of PapR. Significant changes were detected in 12.8 % of the total transcripts. Genes related to amino acid transport and metabolism (16.5 %) and transcription (15 %) were mainly upregulated, whereas genes involved in carbohydrate transport and metabolism (12.7 %) were markedly downregulated. The expression of genes related to transcription, including several transcriptional regulators and proteins involved in tRNA biosynthesis, was increased. The expression levels of genes associated with several transport systems, such as antibiotic, cobalt, and iron complex transporters, was also significantly altered. Among the downregulated genes were transcripts associated with spore formation, the subtilosin A gene cluster, and nitrogen metabolism.

Heterologous expression of polygalacturonase genes isolated from Galactomyces citri-aurantii IJ-1 in Pichia pastoris.

ABSTACT: The objective of this work was to isolate the polygalacturonase genes of Galactomyces citri-aurantii IJ-1 harvested from rotten citrus peels and to heterologously express these genes in Pichia pastoris. Two polygalacturonase (PG) genes from G. citri-aurantii IJ-1 were obtained and tentatively named PG1 and PG2. The genes were cloned into pPICZαC, and expressed in Pichia pastoris strain GS115 with a native signal peptide or the α-factor secretion signal peptide of Saccharomyces cerevisiae. All of the recombinant proteins were successfully secreted into the culture media and confirmed as a single band with a molecular weight of 35 to 38 kDa by SDS-PAGE. The specific enzyme activities of recombinant PG1 and PG2 purified by His-tag affinity resin were 4,749 and 6,719 U/mg, respectively, with an optimal pH and temperature of pH 4.0 and 50°C. The Michaelis-Menten kinetic constants for PG1 and PG2, K (m), were confirmed to be 0.94 and 0.84 mM, respectively. In the presence of Mn(2+), the activity of PG1 and PG2 were increased to 160.8 and 146.4% of normal levels, respectively. In contrast, Cu(2+) and Fe(3+) acted as strong inhibitors to the PGs.

Genome sequencing of Bacillus subtilis SC-8, antagonistic to the Bacillus cereus group, isolated from traditional Korean fermented-soybean food.

Bacillus subtilis SC-8 is a Gram-positive bacterium displaying narrow antagonistic activity for the Bacillus cereus group. B. subtilis SC-8 was isolated from Korean traditional fermented-soybean food. Here we report the draft genome sequence of B. subtilis SC-8, including biosynthetic genes for antibiotics that may have beneficial effects for control of food-borne pathogens.

Characterization of Lactic Acid Bacteria Isolated from Sauce-type Kimchi.

This study was carried out to investigate the isolation and characterization of lactic acid bacteria (LAB) from naturally fermented sauce-type kimchi. Sauce-type kimchi was prepared with fresh, chopped ingredients (Korean cabbage, radish, garlic, ginger, green onion, and red pepper). The two isolated bacteria from sauce-type kimchi were identified as Pediococcus pentosaceus and Lactobacillus brevis by 16S rDNA sequencing and tentatively named Pediococcus sp. IJ-K1 and Lactobacillus sp. IJ-K2, respectively. Pediococcus sp. IJ-K1 was isolated from the early and middle fermentation stages of sauce-type kimchi whereas Lactobacillus sp. IJ-K2 was isolated from the late fermentation stage. The resistance of Pediococcus sp. IJ-K1 and Lactobacillus sp. IJ-K2 to artificial gastric and bile acids led to bacterial survival rates that were 100% and 84.21%, respectively.

Interspecies interaction of signal peptide PapR secreted by Bacillus cereus and its effect on production of antimicrobial peptide.

This study was carried out to investigate the interspecies interaction of PapR peptide secreted by Bacillus cereus on production of BSAP-254, an antimicrobial peptide produced by Bacillus subtilis SC-8 isolated from the Korean fermented soybean paste and exhibited narrow antagonistic activity against the B. cereus group, but not against other foodborne pathogens. PapR is a signal peptide that activates PlcR, which is a pleiotropic regulator controlling the expression of various virulence factors in B. cereus. When B. subtilis SC-8 was co-cultured with B. cereus, it completely inhibited the growth of B. cereus within 12 h, and the rate of BSAP-254 production was increased 34.2% at 12 h. Furthermore, 5 µM of synthetic PapR peptide added to the culture of B. subtilis SC-8 increased the rate of BSAP-254 production up to 59.7%. The growth of B. subtilis SC-8, however, was not significantly different with or without the addition of PapR. When B. cereus papR mutant was co-cultured with B. subtilis SC-8, the growth of the mutant was not inhibited and the rate of BSAP-254 production was decreased by 45%.

Narrow antagonistic activity of antimicrobial peptide from Bacillus subtilis SCK-2 against Bacillus cereus.

Bacillus subtilis SCK-2, producing an antimicrobial peptide of this study, was isolated from Kyeopjang, the Korean traditional fermented-soybean paste. This strain showed a narrow antagonistic activity as it inhibited Bacillus cereus causing food poisoning in human. The antimicrobial peptide, tentatively named AMP IC-1, was purified, characterized, and compared to BSAP-254, another peptide which was previously recovered from traditionally fermented-soybean paste. AMP IC-1 was found to be more thermally stable than BSAP-254, retained inhibitory activity similar to that of BSAP-254 over wide range of pH values, and was also destroyed by proteolytic enzymes. Two compounds were detected by anti-BSAP-254 polyclonal antibody and showed to contain peptide moieties and aliphatic hydrocarbons by Fourier transform infrared analysis. AMP IC-1 had an identical R(f) value (0.69) on TLC plate and a molecular weight similar to that of BSAP-254 (AMP IC-1, m/z 3401; BSAP-254, m/z 3400 to 3473). AMP IC-1 was found to contain about 33 residues and 13 types of amino acids: Cys, Asp or Asn, Glu or Gln, Ser, Gly, Arg, Thr, Ala, Pro, Val, Ile, Leu, and Lys. Compared to BSAP-254, the molar ratios of Asp or Asn, Ser, Val, and Leu were different and only AMP IC-1 contained Arg, but not Trp. Both compounds showed non-hemolytic activity. A partial synergistic effect against B. cereus was observed in response to treatment when AMP IC-1 and BSAP-254 were administered in combination. Therefore, AMP IC-1 is a possible candidate as an antimicrobial agent to prevent food-borne infectious disease in human caused by B. cereus.

Growth inhibition and induction of stress protein, GroEL, of Bacillus cereus exposed to antibacterial peptide isolated from Bacillus subtilis SC-8.

This study was conducted to investigate the antibacterial effect of BSAP-254 on Bacillus cereus with the induced stress proteins. The BSAP-254 is an antimicrobial peptide isolated from soybean-fermenting bacteria, Bacillus subtilis SC-8. It had a narrow spectrum of activity against B. cereus group. The growth inhibitory effect of BSAP-254 (50 µg/mL) reduced the population of B. cereus from >10(8) to 10(4) colony-forming units per milliliter within 30 min. In B. cereus exposed to BSAP-254, 14 intracellular proteins were differentially expressed as determined by 2-DE coupled with MS. Of the differentially expressed proteins identified, the stress protein GroEL, which is heat shock protein, was induced in B. cereus exposed to antibacterial peptide.