Harpin, elicitor of the hypersensitive response produced by the plant pathogen Erwinia amylovora

Synthesis and Biological Evaluation of Disulfides Based on Garlic Extract as Type III Secretion System Inhibitors against Erwinia amylovora

Fire blight, caused by Erwinia amylovora, poses a significant threat to rosaceous plants, such as pears, apples, and hawthorns. The type III secretion system (T3SS) is a critical pathogenicity factor in the pathogenesis of E. amylovora. Disulfide compounds, including those derived from garlic extract, exhibit good bioactivity against both bacteria and fungi. In this study, we synthesized 39 disulfide compounds based on garlic extract and developed a high-throughput screening system incorporating the bacterial luciferase lux reporter gene. Compound 5c was identified as the most effective inhibitor, significantly suppressing the promoter expression of T3SS-related genes, such as hrpA and hrpL, in E. amylovora CFBP1430. Furthermore, compound 5c inhibited the hypersensitive response (HR) triggered by E. amylovora CFBP1430 in tobacco without affecting bacterial growth. Compound 5c also reduced the level of secretion of the pathogenic protein HrpN and diminished the pathogenicity of E. amylovora CFBP1430 in pear infection assays. These findings offer a theoretical foundation for the development of novel T3SS inhibitors aimed at the prevention and control of fire blight disease.

The Harpin-Induced Hypersensitive Reaction in Nicotiana tabacum Requires Wall-Associated Kinase 2

Harpins are proteins secreted by many gram-negative, plant-pathogenic bacteria that stimulate the hypersensitive reaction (HR), a host cell death defence response, when infiltrated into plant leaves as purified proteins. This activity of harpins was first discovered in Nicotiana tabacum (tobacco), which manifests an especially strong and rapid harpin-activated HR that becomes evident within 12-24 h after infiltration. HrpN is the major harpin of the fire blight pathogen Erwinia amylovora. We discovered natural variation in the HrpN-induced HR among tobacco accessions and identified candidate genes using genetic mapping and bulked-segregant analysis with whole genome sequencing. Virus-induced gene silencing of candidate gene Wall-Associated Kinase 2 (WAK2) abrogated the HR in response to HrpN and HpaG, a harpin from the soybean bacterial pustule pathogen Xanthomonas citri pv. glycines. WAK2 silencing also compromised the avirulence activity of harpin HrpZ in the tobacco wildfire pathogen Pseudomonas syringae pv. tabaci. A natural, disruptive mutation in WAK2 correlated with the inability of tobacco accessions to mount the harpin-mediated HR. We conclude that the predicted receptor-like kinase WAK2 is required for the strong HR induced in tobacco leaves by harpin protein infiltration and can potentially mediate resistance to bacterial pathogens based on harpin recognition.

Structure and Functions of NDR1/HIN1-Like (NHL) Proteins in Plant Development and Response to Environmental Stresses

The NON-RACE-SPECIFIC DISEASE RESISTANCE 1/harpin-induced 1-LIKE (NHL) gene family plays pivotal roles, including pathogen resistance, abiotic stress tolerance, and developmental regulation, underscoring their functional versatility in developmental and physiological processes of plants. NHL proteins often localize to the plasma membrane and contain conserved motifs, including the LEA2 and transmembrane domains, enabling dynamic interactions with signalling molecules and transcription factors. The ability of NHL proteins to dimerize and oligomerize further enhances their regulatory potential in signalling pathways. This review explores the structural and functional diversity of NHL proteins including their localizations, interacting proteins, and responses to abiotic and biotic stresses, ion transportation, seed germination, and responses to phytohormones. Future research integrating phylogenetics, and advanced tools including artificial intelligence will unlock the full potential of this gene family for breeding climate-resilient crops and agricultural sustainability.

Specialized metabolites present in Camellia reticulata nectar inhibit the growth of nectar-inhabiting microorganisms

Plant specialized metabolites are species-specific compounds that help plants adapt and survive in constantly changing ecological environments. Nectar contains various specialized metabolites, essential for maintaining nectar homeostasis. In this study, we employed high-performance liquid chromatography (HPLC) to compare the sugar composition between spoilage nectar and natural nectar, with further analysis of variations in color, odor, pH, and hydrogen peroxide (H₂O₂) content. Microbial strains in Camellia reticulata nectar were isolated and identified using the spread plate method coupled with DNA sequencing. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was implemented to characterize metabolite differences between spoilage and natural nectars. Subsequent in vitro experiments were conducted to validate the effects of screened nectar metabolites on the isolated microbial strains. The results showed that some C. reticulata nectar could spoil and deteriorate, which disrupted nectar homeostasis and significantly reduced the pollination efficiency by pollinators. Spoilage nectar had significant differences in color, odor, sugar composition, pH, and H2O2 content compared to natural nectar. The number of microbial species and quantity in spoilage nectar were much higher. The H2O2 content in natural nectar could reach (55.5 ± 1.80) μM, while it was undetectable in spoilage nectar. A total of 15 distinct microbial strains and 364 differential metabolites were isolated and identified from two types of nectar. In vitro experiments demonstrated that H2O2 could inhibit all the bacteria in C. reticulata nectar except Serratia liquefaciens. 12-Methyltetradecanoic Acid inhibited Bacillus subtilis, Curtobacterium flaccumfaciens, and Rothia terrae, and Myristic Acid only inhibited Rothia terrae. The nectar metabolites screened in this study had no effect on the nectar specialist yeast Metschnikowia reukaufii. In conclusion, the findings of this study revealed that C. reticulata nectar regulates the growth of microorganisms through its metabolites to maintain nectar homeostasis and prevent spoilage. This study improves the understanding of the physiological mechanisms of C. reticulata in maintaining nectar homeostasis and provides theoretical support for controlling nectar diseases and sustaining the reproductive fitness of C. reticulata. Future research could focus on further exploring the complex interactions between different metabolites in C. reticulata nectar and a wider range of microorganisms. Moreover, the development of practical applications based on these findings, such as the development of natural preservatives for nectar-related products or the optimization of pollination efficiency in C. reticulata cultivation, could be an important area for future exploration.

Advances in the molecular mechanism of grapevine resistance to fungal diseases

Grapevine is an important economic fruit tree worldwide, but grape production has been plagued by a vast number of fungal diseases, which affect tree vigor and the quality and yield of berries. To seek remedies for such issues, researchers have always been committed to conventional and biotechnological breeding. In recent years, increasing progress has been made in elucidating the molecular mechanisms of grape-pathogenic fungi interactions and resistance regulation. Here, we summarize the current knowledge on the molecular basis of grapevine resistance to fungal diseases, including fungal effector-mediated susceptibility and resistance, resistant regulatory networks in grapevine, innovative approaches of genetic transformation, and strategies to improve grape resistance. Understanding the molecular basis is important for exploring and accurately regulating grape resistance to fungal diseases.

Biocontrol Potential of Endophytic Bacillus velezensis LSR7 Against Rubber Red Root Rot Disease

To obtain an effective bacterial biocontrol strain against the fungal pathogen Ganoderma pseudoferreum, causing rubber tree red root rot disease, healthy rubber tree tissue from Baisha County, Hainan Province, was selected as the isolation source, and bacterial strains with strong antifungal effects against G. pseudoferreum were screened. The strain was identified by molecular biology, in vitro root segment tests, pot growth promotion tests, and genome detection. The strain was further evaluated by biological function tests, genome annotation analysis, and plant defense-related enzyme activity detection. The results show that strain LSR7 had good antagonistic effects against G. pseudoferreum, and the inhibition rate reached 88.49%. The strain LSR7 was identified as Bacillus velezensis by genome sequencing. In a greenhouse environment, LSR7 prevents and treats red root rot disease in rubber trees and promotes the growth of rubber tree seedlings. LSR7 secreted cell wall hydrolases (protease, glucanase, and cellulase), amylases, and siderophores. LSR7 also formed biofilms, facilitating plant colonization. Genome prediction showed that LSR7 secreted multiple antifungal lipopeptides. LSR7 enhanced rubber tree resistance to G. pseudoferreum by increasing the activity of defense enzymes. Bacillus velezensis LSR7 has biocontrol potential and is a candidate strain for controlling red root rot disease in rubber trees.

Transcriptomic Study of Nicotiana tabacum Treated with the Bacterial Protein CspD Reveals Some Specific Abiotic Stress Responses

The ability of a cold-shock protein CspD from Bacillus thuringiensis to protect both dicots and monocots against various pathogens is well confirmed under both greenhouse and field conditions; however, the molecular basis of this phenomenon at the transcriptomic level still remains unexplored. Expression profiles of some marker genes associated with SAR/ISR nonspecific resistance pathways and ROS scavengers were examined in CspD-treated Nicotiana tabacum plants, and the RNA-seq analysis of CspD-treated plants was first carried out. The ISR markers PDF1.2 and PR4 were overexpressed locally in treated tobacco leaves with the maximum 2.4- and 5.7-fold change, respectively, reached 12 h after the leaf treatment with CspD; PDF1.2 was also up-regulated 4.8-fold four days after the inoculation of treated plants with TMV. The ROS scavenger analysis demonstrated overexpression of Cu-Zn superoxide dismutase in both treated (with the maximum 5.4-fold change observed 6 h after the treatment) leaves and leaves from the upper tier ("system" leaves, 6.5-fold change observed 4 days after the treatment). The ROS assay confirmed endogenous accumulation of superoxide in CspD-treated leaves 6 and 24 h after the treatment. An in silico comparative study of Arabidopsis orthologs of highly up-regulated tobacco genes induced by CspD with Arabidopsis genes activated by some other molecular patterns revealed the specific CspD-induced expression of Cu-Zn superoxide dismutase and some other genes associated with light and cold responses. This study may contribute to a better understanding of cross-talking between abiotic stress and nonspecific immunity in plants.

The Past, Present, and Future of Plant Activators Targeting the Salicylic Acid Signaling Pathway

Plant activators have emerged as promising alternatives to conventional crop protection chemicals for managing crop diseases due to their unique mode of action. By priming the plant's innate immune system, these compounds can induce disease resistance against a broad spectrum of pathogens without directly inhibiting their proliferation. Key advantages of plant activators include prolonged defense activity, lower effective dosages, and negligible risk of pathogen resistance development. Among the various defensive pathways targeted, the salicylic acid (SA) signaling cascade has been extensively explored, leading to the successful development of commercial activators of systemic acquired resistance, such as benzothiadiazole, for widespread application in crop protection. While the action sites of many SA-targeting activators have been preliminarily mapped to different steps along the pathway, a comprehensive understanding of their precise mechanisms remains elusive. This review provides a historical perspective on plant activator development and outlines diverse screening strategies employed, from whole-plant bioassays to molecular and transgenic approaches. We elaborate on the various components, biological significance, and regulatory circuits governing the SA pathway while critically examining the structural features, bioactivities, and proposed modes of action of classical activators such as benzothiadiazole derivatives, salicylic acid analogs, and other small molecules. Insights from field trials assessing the practical applicability of such activators are also discussed. Furthermore, we highlight the current status, challenges, and future prospects in the realm of SA-targeting activator development globally, with a focus on recent endeavors in China. Collectively, this comprehensive review aims to describe existing knowledge and provide a roadmap for future research toward developing more potent plant activators that enhance crop health.

Competition for nutrient niches within the apple blossom microbiota antagonizes the initiation of fire blight infection

Changes in the plant microbiota composition are intimately associated with the health of the plant, but factors controlling the microbial community in flowers are poorly understood. In this study, we used apple flowers and fire blight as a model system to investigate the effects of floral microbiota and microbial competition on disease development and suppression. To compare changes in microbial flora with the RNA expression patterns of plants, the flower samples were collected in three different flowering stages (Bud, Popcorn, and Full-bloom). Using advanced sequencing technology, we analyzed the data and conducted both in vitro and in vivo experiments to validate our findings. Our results show that the Erwinia amylovora use arabinogalactan, which is secreted on the flowers, for early colonization of apple flowers. Pantoea agglomerans was more competitive for arabinogalactan than E. amylovora. Additionally, P. agglomerans suppressed the expression of virulence factors of E. amylovora by using arabinose, which is a major component of arabinogalactan, which induces virulence gene expression. The present data provide new insights into developing control strategies for diverse plant diseases, including fire blight, by highlighting the importance of nutrients in disease development or suppression.

Ss4368: Pathogen-Associated Molecular Pattern for Inducing Plant Cell Death and Resistance to Phytophthora capsici

Plant recognition of pathogen-associated molecular patterns (PAMPs) is pivotal in triggering immune responses, highlighting their potential as inducers of plant immunity. However, the number of PAMPs identified and applied in such contexts remains limited. In this study, we characterize a novel PAMP, designated Ss4368, which is derived from Scleromitrula shiraiana. Ss4368 is specifically distributed among a few fungal genera, including Botrytis, Monilinia, and Botryotinia. The transient expression of Ss4368 elicits cell death in a range of plant species. The signaling peptides, three conserved motifs, and cysteine residues (C46, C88, C112, C130, and C148) within Ss4368 are crucial for inducing robust cell death. Additionally, these signaling peptides are essential for the protein's localization to the apoplast. The cell death induced by Ss4368 and its homologous protein, Bc4368, is independent of the SUPPRESSOR OF BIR1-1 (SOBIR1), BRI1-ASSOCIATED KINASE-1 (BAK1), and salicylic acid (SA) pathways. Furthermore, the immune responses triggered by Ss4368 and Bc4368 significantly enhance the resistance of Nicotiana benthamiana to Phytophthora capsici. Therefore, we propose that Ss4368, as a novel PAMP, holds the potential for developing strategies to enhance plant resistance against P. capsici.

Molecular characterization revealed the role of thaumatin-like proteins of Rhizoctonia solani AG4-JY in inducing maize disease resistance

The gene family of thaumatin-like proteins (TLPs) plays a crucial role in the adaptation of organisms to environmental stresses. In recent years, fungal secreted proteins (SP) with inducing disease resistance activity in plants have emerged as important elicitors in the control of fungal diseases. Identifying SPs with inducing disease resistance activity and studying their mechanisms are crucial for controlling sheath blight. In the present study, 10 proteins containing the thaumatin-like domain were identified in strain AG4-JY of Rhizoctonia solani and eight of the 10 proteins had signal peptides. Analysis of the TLP genes of the 10 different anastomosis groups (AGs) showed that the evolutionary relationship of the TLP gene was consistent with that between different AGs of R. solani. Furthermore, it was found that RsTLP3, RsTLP9 and RsTLP10 were regarded as secreted proteins for their signaling peptides exhibited secretory activity. Prokaryotic expression and enzyme activity analysis revealed that the three secreted proteins possess glycoside hydrolase activity, suggesting they belong to the TLP family. Additionally, spraying the crude enzyme solution of the three TLP proteins could enhance maize resistance to sheath blight. Further analysis showed that genes associated with the salicylic acid and ethylene pathways were up-regulated following RsTLP3 application. The results indicated that RsTLP3 had a good application prospect in biological control.

Design and Synthesis of Mandelic Acid Derivatives for Suppression of Virulence via T3SS against Citrus Canker

Citrus canker, a highly contagious bacterial disease caused by Xanthomonas citri subsp. citri (Xcc), poses a substantial threat to citrus crops, leading to serious reductions in fruit yield and economic losses. Most commonly used bactericides against Xcc lead to the rapid development of resistant subpopulations. Therefore, it is imperative to create novel drugs, such as type III secretion system (T3SS) inhibitors, that specifically target bacterial virulence factors rather than bacterial viability. In our study, we designed and synthesized a series of mandelic acid derivatives including 2-mercapto-1,3,4-thiazole. Seven substances were found to reduce the level of transcription of hpa1 without affecting bacterial viability. In vivo bioassays indicated that compound F9 significantly inhibited hypersensitive response and pathogenicity. RT-qPCR assays showed that compound F9 visibly suppressed the expression of Xcc T3SS-related genes as well as citrus canker susceptibility gene CsLOB1. Furthermore, the combination with compound F9 and quorum-quenching bacteria HN-8 can also obviously alleviate canker symptoms.

Screening, identification and evaluation of an acidophilic strain of Bacillus velezensis B4-7 for the biocontrol of tobacco bacterial wilt

Tobacco (Nicotiana tabacum L.) bacterial wilt, caused by Ralstonia solanacearum, is indeed a highly destructive plant disease, leading to substantial damage in tobacco production. While biological control is considered an effective measure for managing bacterial wilt, related research in this area has been relatively limited compared to other control methods. In order to discover new potential antagonistic bacteria with high biocontrol efficacy against tobacco bacterial wilt, we conducted an analysis of the microbial composition differences between disease-suppressive and disease-conducive soils using Illumina sequencing. As a result, we successfully isolated six strains from the disease-suppressive soil that exhibited antibacterial activity against Ralstonia solanacearum. Among these strains, B4-7 showed the strongest antibacterial activity, even at acidic conditions with a pH of 4.0. Based on genome analysis using Average Nucleotide Identity (ANI), B4-7 was identified as Bacillus velezensis. In greenhouse and field trials, strain B4-7 significantly reduced the disease index of tobacco bacterial wilt, with control efficiencies reaching 74.03% and 46.88% respectively. Additionally, B4-7 exhibited plant-promoting abilities that led to a 35.27% increase in tobacco production in field conditions. Quantitative real-time (qPCR) analysis demonstrated that strain B4-7 effectively reduced the abundance of R. solanacearum in the rhizosphere. Genome sequencing and Liquid Chromatography-Mass Spectrometry (LC-MS) analysis revealed that strain B4-7 potentially produces various lipopeptide metabolites, such as microlactin, bacillaene, difficidin, bacilysin, and surfactin. Furthermore, B4-7 influenced the structure of the rhizosphere soil microbial community, increasing bacterial abundance and fungal diversity, while also promoting the growth of different beneficial microorganisms. In addition, B4-7 enhanced tobacco's resistance to R. solanacearum by increasing the activities of defense enzymes, including superoxide dismutase (SOD), phenylalanine ammonia-lyase (PAL), peroxidase (POD), catalase (CAT), and polyphenol oxidase (PPO). Collectively, these findings suggest that B. velezensis B4-7 holds significant biocontrol potential and can be considered a promising candidate strain for eco-friendly management of tobacco bacterial wilt.

Plant Biostimulant as an Environmentally Friendly Alternative to Modern Agriculture

Ensuring the safety of crop production presents a significant challenge to humanity. Pesticides and fertilizers are commonly used to eliminate external interference and provide nutrients, enabling crops to sustain growth and defense. However, the addition of chemical substances does not meet the environmental standards required for agricultural production. Recently, natural sources such as biostimulants have been found to help plants with growth and defense. The development of biostimulants provides new solutions for agricultural product safety and has become a widely utilized tool in agricultural. The review summarizes the classification of biostimulants, including humic-based biostimulant, protein-based biostimulant, oligosaccharide-based biostimulant, metabolites-based biostimulants, inorganic substance, and microbial inoculant. This review attempts to summarize suitable alternative technology that can address the problems and analyze the current state of biostimulants, summarizes the research mechanisms, and anticipates future technological developments and market trends, which provides comprehensive information for researchers to develop biostimulants.

Join the green team: Inducers of plant immunity in the plant disease sustainable control toolbox

BACKGROUND

Crops are constantly attacked by various pathogens. These pathogenic microorganisms, such as fungi, oomycetes, bacteria, viruses, and nematodes, threaten global food security by causing detrimental crop diseases that generate tremendous quality and yield losses worldwide. Chemical pesticides have undoubtedly reduced crop damage; however, in addition to increasing the cost of agricultural production, the extensive use of chemical pesticides comes with environmental and social costs. Therefore, it is necessary to vigorously develop sustainable disease prevention and control strategies to promote the transition from traditional chemical control to modern green technologies. Plants possess sophisticated and efficient defense mechanisms against a wide range of pathogens naturally. Immune induction technology based on plant immunity inducers can prime plant defense mechanisms and greatly decrease the occurrence and severity of plant diseases. Reducing the use of agrochemicals is an effective way to minimize environmental pollution and promote agricultural safety.

AIM OF REVIEW

The purpose of this workis to offer valuable insights into the current understanding and future research perspectives of plant immunity inducers and their uses in plant disease control, ecological and environmental protection, and sustainable development of agriculture.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this work, we have introduced the concepts of sustainable and environment-friendly concepts of green disease prevention and control technologies based on plant immunity inducers. This article comprehensively summarizes these recent advances, emphasizes the importance of sustainable disease prevention and control technologies for food security, and highlights the diverse functions of plant immunity inducers-mediated disease resistance. The challenges encountered in the potential applications of plant immunity inducers and future research orientation are also discussed.

Some Structural Elements of Bacterial Protein MF3 That Influence Its Ability to Induce Plant Resistance to Fungi, Viruses, and Other Plant Pathogens

The ability of the MF3 protein from Pseudomonas fluorescens to protect plants by inducing their resistance to pathogenic fungi, bacteria, and viruses is well confirmed both in greenhouses and in the field; however, the molecular basis of this phenomenon remains unexplored. To find a relationship between the primary (and spatial) structure of the protein and its target activity, we analyzed the inducing activity of a set of mutants generated by alanine scanning and an alpha-helix deletion (ahD) in the part of the MF3 molecule previously identified by our group as a 29-amino-acid peptide working as the inducer on its own. Testing the mutants' inducing activity using the "tobacco-tobacco mosaic virus" pathosystem revealed that some of them showed an almost threefold (V60A and V62A) or twofold (G51A, L58A, ahD) reduction in inducing activity compared to the wild-type MF3 type. Interestingly, these mutations demonstrated close proximity in the homology model, probably contributing to MF3 reception in a host plant.

Plant Elicitor Peptide (Pep) Signaling and Pathogen Defense in Tomato

Endogenous signaling compounds are intermediaries in signaling pathways that plants use to respond to the perception of harmful and beneficial organisms. The plant elicitor peptides (Peps) of plants are important endogenous signaling molecules that induce elements of defense responses such as hormone production, increased expression of defensive genes, the activation of phosphorelays, and the induction of cell secondary messenger synthesis. The processes by which Peps confer resistance to pathogenic microorganisms have been extensively studied in Arabidopsis but are less known in crop plants. Tomato and many other solanaceous plants have an endogenous signaling polypeptide, systemin, that is involved in the defense against herbivorous insects and necrotrophic pathogens. This paper explores the similarity of the effects and chemical properties of Pep and systemin in tomato. Additionally, the relationship of the Pep receptor and systemin receptors is explored, and the identification of a second tomato Pep receptor in the literature is called into question. We suggest future directions for research on Pep signaling in solanaceous crops during interactions with microbes.

Effects of four disease-controlling agents (chlorothalonil, CuCl2, harpin, and melatonin) on postharvest jujube fruit quality

Postharvest senescence and disease development can reduce the nutritional value of fresh jujube fruit. Herein, four different disease-controlling agents (chlorothalonil, CuCl₂, harpin and melatonin) were separately applied to fresh jujube fruit, and all improved postharvest quality (evaluated by disease severity, antioxidant accumulation and senescence) relative to controls. Disease severity was drastically inhibited by these agents, in the order chlorothalonil > CuCl₂ > harpin > melatonin. However, chlorothalonil residues were detected even after storage for 4 weeks. These agents increased the activities of defense enzymes including phenylalanine ammonia-lyase, polyphenol oxidase, glutathione reductase and glutathione S-transferase, as well as accumulation of antioxidant compounds such as ascorbic acid, glutathione, flavonoids and phenolics, in postharvest jujube fruit. The enhanced antioxidant content and antioxidant capacity (evaluated by Fe³⁺ reducing power) was ordered melatonin > harpin > CuCl₂ > chlorothalonil. All four agents significantly delayed senescence (evaluated by weight loss, respiration rate and firmness), with the effect ordered CuCl₂ > melatonin > harpin > chlorothalonil. Moreover, treatment with CuCl₂ also increased copper accumulation ~ threefold in postharvest jujube fruit. Among the four agents, postharvest treatment with CuCl₂ could be considered most appropriate for improving postharvest jujube fruit quality under low temperature conditions without sterilization.

Diverse interactions of five core type III effectors from Ralstonia solanacearum with plants

Ralstonia solanacearum is a widespread plant bacterial pathogen that can launch a range of type III effectors (T3Es) to cause disease. In this study, we isolate a pathogenic R. solanacearum strain named P380 from tomato rhizosphere. Five out of 12 core T3Es of strain P380 are introduced into Pseudomonas syringae DC3000D36E separately to determine their functions in interacting with plants. DC3000D36E that harbors each effector suppresses FliC-triggered Pti5 and ACRE31 expression, ROS burst, and callose deposition. RipAE, RipU, and RipW elicit cell death as well as upregulate the MAPK cascades in Nicotiana benthamiana. The derivatives RipC1ΔDXDX(T/V) and RipWΔDKXXQ but not RipAEK310R fail to suppress ROS burst. Moreover, RipAEK310R and RipWΔDKXXQ retain the cell death elicitation ability. RipAE and RipW are associated with salicylic acid and jasmonic acid pathways, respectively. RipAE and RipAQ significantly promote the propagation of DC3000D36E in plants. The five core T3Es localize in diverse subcellular organelles of nucleus, plasma membrane, endoplasmic reticulum, and Golgi network. The suppressor of G2 allele of Skp1 is required for RipAE but not RipU-triggered cell death in N. benthamiana. These results indicate that the core T3Es in R. solanacearum play diverse roles in plant-pathogen interactions.

Biotechnologically Engineered Plants

The development of recombinant DNA technology during the past thirty years has enabled scientists to isolate, characterize, and manipulate a myriad of different animal, bacterial, and plant genes. This has, in turn, led to the commercialization of hundreds of useful products that have significantly improved human health and well-being. Commercially, these products have been mostly produced in bacterial, fungal, or animal cells grown in culture. More recently, scientists have begun to develop a wide range of transgenic plants that produce numerous useful compounds. The perceived advantage of producing foreign compounds in plants is that compared to other methods of producing these compounds, plants seemingly provide a much less expensive means of production. A few plant-produced compounds are already commercially available; however, many more are in the production pipeline.

Discovery of the Hrp Type III Secretion System in Phytopathogenic Bacteria: How Investigation of Hypersensitive Cell Death in Plants Led to a Novel Protein Injector System and a World of Inter-Organismal Molecular Interactions Within Plant Cells

In the early 1960s, Pseudomonas syringae and other host-specific phytopathogenic proteobacteria were discovered to elicit a rapid, resistance-associated death when infiltrated at high inoculum levels into nonhost tobacco leaves. This hypersensitive reaction (or response; HR) was a useful indicator of basic pathogenic ability. Research over the next 20 years failed to identify an elicitor of the HR but revealed that its elicitation required contact between metabolically active bacterial and plant cells. Beginning in the early 1980s, molecular genetic tools were applied to the HR puzzle, revealing the presence in P. syringae of clusters of hrp genes, so named because they are required for the HR and pathogenicity, and of avr genes, so named because their presence confers HR-associated avirulence in resistant cultivars of a host plant species. A series of breakthroughs over the next two decades revealed that (i) hrp gene clusters encode a type III secretion system (T3SS), which injects Avr (now "effector") proteins into plant cells, where their recognition triggers the HR; (ii) T3SSs, which are typically present in pathogenicity islands acquired by horizontal gene transfers, are found in many bacterial pathogens of plants and animals and inject many effector proteins, which are collectively essential for pathogenicity; and (iii) a primary function of phytopathogen effectors is to subvert non-HR defenses resulting from recognition of conserved microbial features presented outside of plant cells. In the 2000s, Hrp system research shifted to extracellular components enabling effector delivery across plant cell walls and plasma membranes, regulation, and tools for studying effectors. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Characteristics, Roles and Applications of Proteinaceous Elicitors from Pathogens in Plant Immunity

In interactions between pathogens and plants, pathogens secrete many molecules that facilitate plant infection, and some of these compounds are recognized by plant pattern recognition receptors (PRRs), which induce immune responses. Molecules in both pathogens and plants that trigger immune responses in plants are termed elicitors. On the basis of their chemical content, elicitors can be classified into carbohydrates, lipopeptides, proteinaceous compounds and other types. Although many studies have focused on the involvement of elicitors in plants, especially on pathophysiological changes induced by elicitors in plants and the mechanisms mediating these changes, there is a lack of up-to-date reviews on the characteristics and functions of proteinaceous elicitors. In this mini-review, we provide an overview of the up-to-date knowledge on several important families of pathogenic proteinaceous elicitors (i.e., harpins, necrosis- and ethylene-inducing peptide 1 (nep1)-like proteins (NLPs) and elicitins), focusing mainly on their structures, characteristics and effects on plants, specifically on their roles in plant immune responses. A solid understanding of elicitors may be helpful to decrease the use of agrochemicals in agriculture and gardening, generate more resistant germplasms and increase crop yields.

Enhanced Resistance to Sclerotinia sclerotiorum in Brassica rapa by Activating Host Immunity through Exogenous Verticillium dahliae Aspf2-like Protein (VDAL) Treatment

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most destructive diseases in Brassica rapa. Verticillium dahliae Aspf2-like protein (VDAL) is a secretory protein of V. dahliae which has been shown to enhance the resistance against fungal infections in several plants. Nonetheless, the molecular mechanisms of VDAL-primed disease resistance are still poorly understood. In this study, we performed physiological, biochemical, and transcriptomic analyses of Brassica rapa in order to understand how VDAL confers resistance to S. sclerotiorumn infections in plants. The results showed that foliar application of VDAL significantly reduced the plaque area on leaves inoculated with S. sclerotiorum. It also enhanced antioxidant capacity by increasing activities of superoxide dismutase (SOD), peroxidase (POD), peroxidase (APX), glutathione reductase (GR), protoporphyrinogen oxidase (PPO), and defense-related enzymes β-1,3-glucanase and chitinase during the infection periods. This occurred in parallel with significantly reduced relative conductivity at different periods and lower malondialdehyde (MDA) content as compared to sole S. sclerotiorum inoculation. Transcriptomic analysis showed a total of 146 (81 up-regulated and 65 down-regulated) differentially expressed genes (DEGs) in VDAL-treated leaves compared to the control. The most enriched three Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were the mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signal transduction, and plant-pathogen interaction, all of which were associated with plant immunity. DEGs associated with MAPK and hormone signal transduction pathways were ethylene response sensor ERS2, EIN3 (Ethylene Insensitive3)-binding F-box protein 2 (EBF2), ethylene-responsive transcription factor ERF94, MAPK 9 (MKK9), protein phosphatase 2C (PP2C37), auxin-responsive proteins (AUX/IAA1 and 19), serine/threonine-protein kinase CTR1, and abscisic acid receptors (PLY 4 and 5). Among the DEGs linked with the plant-pathogen interaction pathway were calmodulin-like proteins (CML5, 24, 27), PTI1-like tyrosine protein kinase 3 (Pti13) and transcription factor MYB30, all of which are known to play key roles in pathogen-associated molecular pattern (PAMP)-triggered immunity and effector-triggered immunity (ETI) for hypersensitive response (HR), cell wall reinforcement, and stomatal closure in plants. Overall, VDLA treatment triggered repression of the auxin and ABA signaling pathways and de-repression of the ethylene signaling pathways in young B. rapa seedlings to increase plant innate immunity. Our results showed that VDAL holds great potential to enhance fungal disease resistance in B. rapa crop.

Putative transcription antiterminator RfaH contributes to Erwinia amylovora virulence

The gram-negative bacterium Erwinia amylovora causes fire blight disease of apple and pear trees. The exopolysaccharide amylovoran and lipopolysaccharides are essential E. amylovora virulence factors. Production of amylovoran and lipopolysaccharide is specified in part by genes that are members of long operons. Here, we show that full virulence of E. amylovora in apple fruitlets and tree shoots depends on the predicted transcription antiterminator RfaH. RfaH reduces pausing in the production of long transcripts having an operon polarity suppressor regulatory element within their promoter region. In E. amylovora, only the amylovoran operon and a lipopolysaccharide operon have such regulatory elements within their promoter regions and in the correct orientation. These operons showed dramatically increased polarity in the ΔrfaH mutant compared to the wild type as determined by RNA sequencing. Amylovoran and lipopolysaccharide production in vitro was reduced in rfaH mutants compared to the wild type, which probably contributes to the rfaH mutant virulence phenotype. Furthermore, type VI secretion cluster 1, which contributes to E. amylovora virulence, showed reduced expression in ΔrfaH compared to the wild type, although without an increase in polarity. The data suggest that E. amylovora RfaH directly, specifically, and exclusively suppresses operon polarity in the amylovoran operon and a lipopolysaccharide operon.

Advances in Fungal Elicitor-Triggered Plant Immunity

There is an array of pathogenic fungi in the natural environment of plants, which produce some molecules including pathogen-associated molecular patterns (PAMPs) and effectors during infection. These molecules, which can be recognized by plant specific receptors to activate plant immunity, including PTI (PAMP-triggered immunity) and ETI (effector-triggered immunity), are called elicitors. Undoubtedly, identification of novel fungal elicitors and their plant receptors and comprehensive understanding about fungal elicitor-triggered plant immunity will be of great significance to effectively control plant diseases. Great progress has occurred in fungal elicitor-triggered plant immunity, especially in the signaling pathways of PTI and ETI, in recent years. Here, recent advances in fungal elicitor-triggered plant immunity are summarized and their important contribution to the enlightenment of plant disease control is also discussed.

The heterologous expression of conserved Glycine max (soybean) mitogen activated protein kinase 3 (MAPK3) paralogs suppresses Meloidogyne incognita parasitism in Gossypium hirsutum (upland cotton)

Two conserved Glycine max (soybean) mitogen activated protein kinase 3 (MAPK3) paralogs function in defense to the parasitic soybean cyst nematode Heterodera glycines. Gene Ontology analyses of RNA seq data obtained from MAPK3-1-overexpressing (OE) and MAPK3-2-OE roots compared to their control, as well as MAPK3-1-RNA interference (RNAi) and MAPK3-2-RNAi compared to their control, hierarchically orders the induced and suppressed genes, strengthening the hypothesis that their heterologous expression in Gossypium hirsutum (upland cotton) would impair parasitism by the root knot nematode (RKN) Meloidogyne incognita. MAPK3-1 expression (E) in G. hirsutum suppresses the production of M. incognita root galls, egg masses, and second stage juveniles (J2s) by 80.32%, 82.37%, and 88.21%, respectfully. Unexpectedly, egg number increases by 28.99% but J2s are inviable. MAPK3-2-E effects are identical, statistically. MAPK3-1-E and MAPK3-2-E decreases root mass 1.49-fold and 1.55-fold, respectively, as compared to the pRAP15-ccdB-E control. The reproductive factor (RF) of M. incognita for G. hirsutum roots expressing MAPK3-1-E or MAPK3-2-E decreases 60.39% and 50.46%, respectively, compared to controls. The results are consistent with upstream pathogen activated molecular pattern (PAMP) triggered immunity (PTI) and effector triggered immunity (ETI) functioning in defense to H. glycines. The experiments showcase the feasibility of employing MAPK3, through heterologous expression, to combat M. incognita parasitism, possibly overcoming impediments otherwise making G. hirsutum's defense platform deficient. MAPK homologs are identified in other important crop species for future functional analyses.

TOUCH 3 and CALMODULIN 1/4/6 cooperate with calcium-dependent protein kinases to trigger calcium-dependent activation of CAM-BINDING PROTEIN 60-LIKE G and regulate fungal resistance in plants

Plants utilize localized cell-surface and intracellular receptors to sense microbes and activate the influx of calcium, which serves as an important second messenger in eukaryotes to regulate cellular responses. However, the mechanisms through which plants decipher calcium influx to activate immune responses remain largely unknown. Here, we show that pathogen-associated molecular patterns (PAMPs) trigger calcium-dependent phosphorylation of CAM-BINDING PROTEIN 60-LIKE G (CBP60g) in Arabidopsis (Arabidopsis thaliana). CALCIUM-DEPENDENT PROTEIN KINASE5 (CPK5) phosphorylates CBP60g directly, thereby enhancing its transcription factor activity. TOUCH 3 (TCH3) and its homologs CALMODULIN (CAM) 1/4/6 and CPK4/5/6/11 are required for PAMP-induced CBP60g phosphorylation. TCH3 interferes with the auto-inhibitory region of CPK5 and promotes CPK5-mediated CBP60g phosphorylation. Furthermore, CPKs-mediated CBP60g phosphorylation positively regulates plant resistance to soil-borne fungal pathogens. These lines of evidence uncover a novel calcium signal decoding mechanism during plant immunity through which TCH3 relieves auto-inhibition of CPK5 to phosphorylate and activate CBP60g. The findings reveal cooperative interconnections between different types of calcium sensors in eukaryotes.

Leaf proteome reveals the alterations in photosynthesis and defense-related proteins between potato tetraploid cultivars and diploid wild species

Potato (Solanum tuberosum L.) as the important food crop worldwide has abundant morphological and genetic diversity. To understand the underlying molecular mechanisms determining phenotypic differences in wild species and cultivated potato, a comparative proteomics approach was applied to analyze leaf proteome alteration among three tetraploid cultivars and three diploid wild species using two-dimensional gel electrophoresis (2-DE). Quantitative image analysis showed a total of 47 protein spots with significantly altered abundance (>3-fold, P < 0.05), and 45 differentially abundant proteins were identified by MALDI-TOF/TOF MS. These proteins exhibited both the qualitative and quantitative changes. Most of them were involved in photosynthesis, cell defense and rescue, protein biosynthesis, which might exhibit the main differences between tetraploid cultivars and diploid wild species. The photosynthesis and protein biosynthesis-related proteins were up-regulated or only present in tetraploid cultivars, suggesting the higher photosynthetic efficiency and more newly synthesized peptides. It might contribute to some superior traits of tetraploid cultivars, such as larger leaf size, greater growth vigor, better tuber yield and quality. However, some cell defense and rescue-related proteins, especially the pathogenesis-related proteins and antioxidant enzymes, were up-regulated or only present in diploid wild species. It might be responsible for stronger resistance to diseases and pests or tolerance to environmental stresses in diploid wild species. This study would provide valuable information for the underlying molecular mechanisms of potato genetic diversity, and help in developing strategies for the utilization of wild species for potato improvement.

Essential Acidovorax citrulli Virulence Gene hrpE Activates Host Immune Response against Pathogen

Bacterial fruit blotch (BFB) caused by Acidovorax citrulli (Ac) is a devastating watermelon disease that severely impacts the global watermelon industry. Like other Gram-negative bacteria, the type three secretion system (T3SS) is the main pathogenicity factor of A. citrulli. The T3SS apparatus gene hrpE codes for the Hrp pilus and serves as a conduit to secret effector proteins into host cells. In this study, we found that the deletion of hrpE in A. citrulli results in the loss of pathogenicity on hosts and the hypersensitive response on non-hosts. In addition, the A. citrulli hrpE mutant showed a reduction in in vitro growth, in planta colonization, swimming and twitching motility, and displayed increases in biofilm formation ability compared to the wild type. However, when HrpE was transiently expressed in hosts, the defense responses, including reactive oxygen species bursts, callose deposition, and expression of defense-related genes, were activated. Thus, the A. Citrulli growth in HrpE-pretreated hosts was suppressed. These results indicated that HrpE is essential for A. citrulli virulence but can also be used by hosts to help resist A. citrulli. Our findings provide a better understanding of the T3SS pathogenesis in A. citrulli, thus providing a molecular basis for biopesticide development, and facilitating the effective control of BFB.

Identification of novel virulence factors in Erwinia amylovora through temporal transcriptomic analysis of infected apple flowers under field conditions

The enterobacterial pathogen Erwinia amylovora uses multiple virulence-associated traits to cause fire blight, a devastating disease of apple and pear trees. Many virulence-associated phenotypes have been studied that are critical for virulence and pathogenicity. Despite the in vitro testing that has revealed how these systems are transcriptionally regulated, information on when and where in infected tissues these genes are being expressed is lacking. Here, we used a high-throughput sequencing approach to characterize the transcriptome of E. amylovora during disease progression on apple flowers under field infection conditions. We report that type III secretion system genes and flagellar genes are strongly co-expressed. Likewise, genes involved in biosynthesis of the exopolysaccharide amylovoran and sorbitol utilization had similar expression patterns. We further identified a group of 16 genes whose expression is increased and maintained at high levels throughout disease progression across time and tissues. We chose five of these genes for mutational analysis and observed that deletion mutants lacking these genes all display reduced symptom development on apple shoots. Furthermore, these induced genes were over-represented for genes involved in sulphur metabolism and cycling, suggesting the possibility of an important role for maintenance of oxidative homeostasis during apple flower infection.

Glycine max Homologs of DOESN'T MAKE INFECTIONS 1, 2, and 3 Function to Impair Heterodera glycines Parasitism While Also Regulating Mitogen Activated Protein Kinase Expression

Glycine max root cells developing into syncytia through the parasitic activities of the pathogenic nematode Heterodera glycines underwent isolation by laser microdissection (LM). Microarray analyses have identified the expression of a G. max DOESN'T MAKE INFECTIONS3 (DMI3) homolog in syncytia undergoing parasitism but during a defense response. DMI3 encodes part of the common symbiosis pathway (CSP) involving DMI1, DMI2, and other CSP genes. The identified DMI gene expression, and symbiosis role, suggests the possible existence of commonalities between symbiosis and defense. G. max has 3 DMI1, 12 DMI2, and 2 DMI3 paralogs. LM-assisted gene expression experiments of isolated syncytia under further examination here show G. max DMI1-3, DMI2-7, and DMI3-2 expression occurring during the defense response in the H. glycines-resistant genotypes G.max [Peking/PI548402] and G.max [PI88788] indicating a broad and consistent level of expression of the genes. Transgenic overexpression (OE) of G. max DMI1-3, DMI2-7, and DMI3-2 impairs H. glycines parasitism. RNA interference (RNAi) of G. max DMI1-3, DMI2-7, and DMI3-2 increases H. glycines parasitism. The combined opposite outcomes reveal a defense function for these genes. Prior functional transgenic analyses of the 32-member G. max mitogen activated protein kinase (MAPK) gene family has determined that 9 of them act in the defense response to H. glycines parasitism, referred to as defense MAPKs. RNA-seq analyses of root RNA isolated from the 9 G. max defense MAPKs undergoing OE or RNAi reveal they alter the relative transcript abundances (RTAs) of specific DMI1, DMI2, and DMI3 paralogs. In contrast, transgenically-manipulated DMI1-3, DMI2-7, and DMI3-2 expression influences MAPK3-1 and MAPK3-2 RTAs under certain circumstances. The results show G. max homologs of the CSP, and defense pathway are linked, apparently involving co-regulated gene expression.

Search for host defense markers uncovers an apple agglutination factor corresponding with fire blight resistance

Pathenogenesis-related (PR) proteins are extensively used as molecular markers to dissect the signaling cascades leading to plant defense responses. However, studies focusing on the biochemical or biological properties of these proteins remain rare. Here, we identify and characterize a class of apple (Malus domestica) PR proteins, named M. domestica AGGLUTININS (MdAGGs), belonging to the amaranthin-like lectin family. By combining molecular and biochemical approaches, we show that abundant production of MdAGGs in leaf tissues corresponds with enhanced resistance to the bacterium Erwinia amylovora, the causal agent of the disease fire blight. We also show that E. amylovora represses the expression of MdAGG genes by injecting the type 3 effector DspA/E into host cells and by secreting bacterial exopolysaccharides. Using a purified recombinant MdAGG, we show that the protein agglutinates E. amylovora cells in vitro and binds bacterial lipopolysaccharides at low pH, conditions reminiscent of the intercellular pH occurring in planta upon E. amylovora infection. We finally provide evidence that negatively charged polysaccharides, such as the free exopolysaccharide amylovoran progressively released by the bacteria, act as decoys relying on charge-charge interaction with the MdAGG to inhibit agglutination. Overall, our results suggest that the production of this particular class of PR proteins may contribute to apple innate immunity mechanisms active against E. amylovora.

The Effects of Exercise on Aging-Induced Exaggerated Cytokine Responses: An Interdisciplinary Discussion

Aging is generally known to be associated with dynamic biological changes, physiological dysfunction, and environmental and psychological decline. Several studies have suggested that aging is associated with increased inflammatory cytokines, causing several diseases. However, the effect of exercise on aging has been less delineated, and the relationships between cytokine activation, aging, and exercise also need further study. Here, we discuss some ideas about the effect of exercise on aging-induced exaggerated cytokine responses and discuss the possible roles of the aging-induced exaggerated cytokine response following exercise. Evidence from these findings suggests that exercise is a beneficially applicable model to use in studies on the mechanisms underlying the age-associated gradated cytokine response, and these results may provide guidelines for health professionals with diverse backgrounds.

Plant immunity inducers: from discovery to agricultural application

While conventional chemical fungicides directly eliminate pathogens, plant immunity inducers activate or prime plant immunity. In recent years, considerable progress has been made in understanding the mechanisms of immune regulation in plants. The development and application of plant immunity inducers based on the principles of plant immunity represent a new field in plant protection research. In this review, we describe the mechanisms of plant immunity inducers in terms of plant immune system activation, summarize the various classes of reported plant immunity inducers (proteins, oligosaccharides, chemicals, and lipids), and review methods for the identification or synthesis of plant immunity inducers. The current situation, new strategies, and future prospects in the development and application of plant immunity inducers are also discussed.

Bacterial type III effector-induced plant C8 volatiles elicit antibacterial immunity in heterospecific neighbouring plants via airborne signalling

Upon sensing attack by pathogens and insect herbivores, plants release complex mixtures of volatile compounds. Here, we show that the infection of lima bean (Phaseolus lunatus L.) plants with the non-host bacterial pathogen Pseudomonas syringae pv. tomato led to the production of microbe-induced plant volatiles (MIPVs). Surprisingly, the bacterial type III secretion system, which injects effector proteins directly into the plant cytosol to subvert host functions, was found to prime both intra- and inter-specific defense responses in neighbouring wild tobacco (Nicotiana benthamiana) plants. Screening of each of 16 effectors using the Pseudomonas fluorescens effector-to-host analyser revealed that an effector, HopP1, was responsible for immune activation in receiver tobacco plants. Further study demonstrated that 1-octen-3-ol, 3-octanone and 3-octanol are novel MIPVs emitted by the lima bean plant in a HopP1-dependent manner. Exposure to synthetic 1-octen-3-ol activated immunity in tobacco plants against a virulent pathogen Pseudomonas syringae pv. tabaci. Our results show for the first time that a bacterial type III effector can trigger the emission of C8 plant volatiles that mediate defense priming via plant-plant interactions. These results provide novel insights into the role of airborne chemicals in bacterial pathogen-induced inter-specific plant-plant interactions.

Efficient expression and purification of soluble HarpinEa protein by translation initiation region codon optimization

HarpinEa protein can stimulate plants to produce defense responses to resist the attack of pathogens, improve plant immune resistance, and promote plant growth. This has extremely high application value in agriculture. To efficiently express soluble HarpinEa protein, in this study, we expressed HarpinEa protein with a 6× His-tag in Escherichia coli BL21 (DE3). Because of the low level of expression of HarpinEa protein in E. coli, three rounds of synonymous codon optimization were performed on the +53 bp of the translation initiation region (TIR) of HarpinEa. Soluble HarpinEa protein after optimization accounted for 50.3% of the total soluble cellular protein expressed. After purification using a Ni Bestarose Fast Flow column, the purity of HarpinEa protein exceeded 95%, and the yield reached 227.5 mg/L of culture medium. The purified HarpinEa protein was sensitive to proteases and exhibited thermal stability. It triggered visible hypersensitive responses after being injected into tobacco leaves for 48 h. Plants treated with HarpinEa showed obvious growth-promoting and resistance-improving performance. Thus, the use of TIR synonymous codon optimization successfully achieved the economical, efficient, and soluble production of HarpinEa protein.

Genetic Dissection of the Erwinia amylovora Disease Cycle

Fire blight, caused by the bacterial phytopathogen Erwinia amylovora, is an economically important and mechanistically complex disease that affects apple and pear production in most geographic production hubs worldwide. We compile, assess, and present a genetic outlook on the progression of an E. amylovora infection in the host. We discuss the key aspects of type III secretion-mediated infection and systemic movement, biofilm formation in xylem, and pathogen dispersal via ooze droplets, a concentrated suspension of bacteria and exopolysaccharide components. We present an overall outlook on the genetic elements contributing to E. amylovora pathogenesis, including an exploration of the impact of floral microbiomes on E. amylovora colonization, and summarize the current knowledge of host responses to an incursion and how this response stimulates further infection and systemic spread. We hope to facilitate the identification of new, unexplored areas of research in this pathosystem that can help identify evolutionarily susceptible genetic targets to ultimately aid in the design of sustainable strategies for fire blight disease mitigation.

Functional Characterization of VDACs in Grape and Its Putative Role in Response to Pathogen Stress

Voltage-dependent anion channels (VDACs) are the most abundant proteins in the mitochondrial outer membranes of all eukaryotic cells. They participate in mitochondrial energy metabolism, mitochondria-mediated apoptosis, and cell growth and reproduction. Here, the chromosomal localizations, gene structure, conserved domains, and phylogenetic relationships were analyzed. The amino acid sequences of VDACs were found to be highly conserved. The tissue-specific transcript analysis from transcriptome data and qRT-PCR demonstrated that grapevine VDACs might play an important role in plant growth and development. It was also speculated that VDAC3 might be a regulator of modulated leaf and berry development as the expression patterns during these developmental stages are up-regulated. Further, we screened the role of all grape VDACs' response to pathogen stress and found that VDAC3 from downy mildew Plasmopara viticola-resistant Chinese wild grapevine species Vitis piasezkii "Liuba-8" had a higher expression than the downy mildew susceptible species Vitis vinifera cv. "Thompson Seedless" after inoculation with P. viticola. Overexpression of VpVDAC3 resulted in increased resistance to pathogens, which was found to prevent VpVDAC3 protein accumulation through protein post-transcriptional regulation. Taken together, these data indicate that VpVDAC3 plays a role in P. viticola defense and provides the evidence with which to understand the mechanism of grape response to pathogen stress.

Cloning and expression of the EsxA gene and the growth-promoting effects of the encoded protein on rice seedlings

An EsxA-encoding gene (esxA) was previously identified in the genome of the plant growth-promoting rhizobacterium Paenibacillus terrae strain NK3-4. The esxA was cloned and expressed in Pichia pastoris, after which the effects of the EsxA protein on rice seedling growth were analyzed to determine whether EsxA contributes to the plant growth-promoting activity of strain NK3-4. The esxA was successfully cloned from the NK3-4 genome and ligated to the eukaryotic expression vector pPICZαA. The resulting pPICZαA-esxA recombinant plasmid was transinfected into yeast cells, and esxA expression in the yeast cells was confirmed. The treatment of seed- buds with the EsxA protein increased the root length by 1.35-times, but decreased the bud length. Additionally, in rice seedlings treated with EsxA, the root and shoot lengths increased by 2.6- and 1.7-times, respectively. These findings imply that EsxA is important for the promotion of rice plant growth by P. terrae strain NK3-4. Furthermore, the construction of the esxA expression vector and the engineered strain may be useful for future investigations of the mechanism underlying the plant growth-promoting effects of EsxA, with implications for the application of EsxA for regulating plant growth.

The N-terminus of an Ustilaginoidea virens Ser-Thr-rich glycosylphosphatidylinositol-anchored protein elicits plant immunity as a MAMP

Many pathogens infect hosts through specific organs, such as Ustilaginoidea virens, which infects rice panicles. Here, we show that a microbe-associated molecular pattern (MAMP), Ser-Thr-rich Glycosyl-phosphatidyl-inositol-anchored protein (SGP1) from U. virens, induces immune responses in rice leaves but not panicles. SGP1 is widely distributed among fungi and acts as a proteinaceous, thermostable elicitor of BAK1-dependent defense responses in N. benthamiana. Plants specifically recognize a 22 amino acid peptide (SGP1 N terminus peptide 22, SNP22) in its N-terminus that induces cell death, oxidative burst, and defense-related gene expression. Exposure to SNP22 enhances rice immunity signaling and resistance to infection by multiple fungal and bacterial pathogens. Interestingly, while SGP1 can activate immune responses in leaves, SGP1 is required for U. virens infection of rice panicles in vivo, showing it contributes to the virulence of a panicle adapted pathogen.

Ustilaginoidea virens is a fungal pathogen that infects rice via the panicles. Here, the authors show that U. virens SGP1, a conserved Ser-Thr-rich glycosyl-phosphatidyl-inositol-anchored protein, elicits immune responses in rice leaves while contributing to virulence in panicles.

Genome Analysis of Erwinia amylovora Strains Responsible for a Fire Blight Outbreak in Korea

Erwinia amylovora is a plant-pathogenic bacterium that causes fire blight disease in Rosaceae plants. Since fire blight is highly contagious and results in serious losses once introduced, it is regulated as a quarantine disease. Recently, for the first time in East Asia, fire blight emerged in Korea with strains of E. amylovora being isolated from lesions of infected trees. Five of those strains were selected and subjected to whole-genome shotgun sequencing. Each strain had two circular replicons, a 3.8-Mb chromosome and a 28-kb plasmid. The genome sequences were compared with those of other E. amylovora strains isolated from different hosts or geographical regions. Genome synteny was analyzed and sequence variations including nucleotide substitutions, inversions, insertions, and deletions were detected. Analysis of the population genomic structure revealed that the five strains form a distinct structural group. Phylogenomic analysis was performed to infer the evolutionary relationships among E. amylovora strains, which indicated that the Korean isolates, all descended from a common ancestor, are closely related to a lineage of North American strains. These results provide useful information for understanding the genomic dynamics of E. amylovora strains including those in Korea, developing genetic markers for surveillance of the pathogen or diagnosis of the disease, and eventually developing measures to eradicate it.

Regulatory role of receptor-like cytoplasmic kinases in early immune signaling events in plants

Receptor-like cytoplasmic kinases (RLCKs) play crucial roles in regulating plant development and immunity. Conserved pathogen-associated molecular patterns (PAMPs) derived from microbes are recognized by plant pattern recognition receptors to activate PAMP-triggered immunity (PTI). Microbial effectors, whose initial function is to promote virulence, are recognized by plant intracellular nucleotide-binding domain and leucine-rich repeat receptors (NLRs) to initiate effector-triggered immunity (ETI). Both PTI and ETI trigger early immune signaling events including the production of reactive oxygen species, induction of calcium influx and activation of mitogen-activated protein kinases. Research progress has revealed the important roles of RLCKs in the regulation of early PTI signaling. Accordingly, RLCKs are often targeted by microbial effectors that are evolved to evade PTI via diverse modulations. In some cases, modulation of RLCKs by microbial effectors triggers the activation of NLRs. This review covers the mechanisms by which RLCKs engage diverse substrates to regulate early PTI signaling and the regulatory roles of RLCKs in triggering NLR activation. Accumulating evidence suggests evolutionary links and close connections between PAMP- and effector-triggered early immune signaling that are mediated by RLCKs. As key immune regulators, RLCKs can be considered targets with broad prospects for the improvement of plant resistance via genetic engineering.

Response of hrpZPsph-transgenic N. benthamiana plants under cadmium stress

The hrpZPsph gene from Pseudomonas syringae pv. phaseolicola, in its secretable form (SP/hrpZPsph), has previously proven capable of conferring resistance against rhizomania disease as well as abiotic stresses in Nicotiana benthamiana plants, while enhancing plant growth. This study aimed at investigating the response of SP/hrpZPsph-expressing plants under cadmium stress. Transgenic N. benthamiana lines, homozygous for the SP/hrpZPsph gene, and wild-type plants were exposed to Cd at different stress levels (0, 50, 100, 150 μΜ CdCl2). Plants' response to stress was assessed at germination and at the whole plant level on the basis of physiological and growth parameters, including seed germination percentage, shoot and root length, total chlorophyll content, fresh and dry root weight, as well as overall symptomatology, and Cd content in leaves and roots. At germination phase, significant differences were noted in germination rates and post-germination growth among stress levels, with Cd effects being in most cases analogous to the level applied but also among plant categories. Although seedling growth was adversely affected in all plant categories, especially at high stress level, lines #6 and #9 showed the lowest decrease in root and shoot length over control. The superiority of these lines was further manifested at the whole plant level by the absence of stress-attributed symptoms and the low or zero reduction in chlorophyll content. Interestingly, a differential tissue-specific Cd accumulation pattern was observed in wt- and hrpZPsph-plants, with the former showing an increased Cd content in leaves and the latter retaining Cd in the roots. These data are discussed in the context of possible mechanisms underlying the hrpZPsph-based Cd stress resistance.

Coiled-Coil N21 of Hpa1 in Xanthomonas oryzae pv. oryzae Promotes Plant Growth, Disease Resistance and Drought Tolerance in Non-Hosts via Eliciting HR and Regulation of Multiple Defense Response Genes

Acting as a typical harpin protein, Hpa1 of Xanthomonas oryzae pv. oryzae is one of the pathogenic factors in hosts and can elicit hypersensitive responses (HR) in non-hosts. To further explain the underlying mechanisms of its induced resistance, we studied the function of the most stable and shortest three heptads in the N-terminal coiled-coil domain of Hpa1, named N21Hpa1. Proteins isolated from N21-transgenic tobacco elicited HR in Xanthi tobacco, which was consistent with the results using N21 and full-length Hpa1 proteins expressed in Escherichia coli. N21-expressing tobacco plants showed enhanced resistance to tobacco mosaic virus (TMV) and Pectobacterium carotovora subsp. carotovora (Pcc). Spraying of a synthesized N21 peptide solution delayed the disease symptoms caused by Botrytis cinerea and Monilinia fructicola and promoted the growth and drought tolerance of plants. Further analysis indicated that N21 upregulated the expression of multiple plant defense-related genes, such as genes mediated by salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) signaling, and genes related to reactive oxygen species (ROS) biosynthesis. Further, the bioavailability of N21 peptide was better than that of full-length Hpa1Xoo. Our studies support the broad application prospects of N21 peptide as a promising succedaneum to biopesticide Messenger or Illite or other biological pharmaceutical products, and provide a basis for further development of biopesticides using proteins with similar structures.