Elicitor Molecules Research Articles

Molecular Mechanisms and Cytopathology of Phytophthora: Strategies, Interactions and Future Perspectives

Phytophthora is an aggressive plant pathogen, pose substantial threats to global agriculture, leading to extensive crop losses. Controlling Phytophthora diseases remains challenging, with limited effective methods available. Host resistance emerges as a promising strategy, but its sustainability hinges on a profound comprehension of the intricate molecular dynamics governing Phytophthora-plant interactions. These interactions unveil a hemi-biotrophic lifestyle of Phytophthora, transitioning from biotrophic to necrotrophic phases during infection. The infection process involves a series of orchestrated events, including chemotactic attraction, penetration, and sporulation on the host surface. Molecular cytology elucidates a sophisticated interplay between Phytophthora and plant defense mechanisms. Phytophthora elicits defense responses in host plants through the release of elicitor molecules, triggering PAMP Triggered Immunity (PTI) responses such as antimicrobial compound production and cell wall fortification. Detection and recognition of Phytophthora effectors instigate a second layer of defense in resistant plants, leading to Effector Triggered Immunity (ETI) and hypersensitive response. In response, virulent strains evolve altered effectors to evade detection and suppress host defenses, underscoring the ongoing molecular coevolution between Phytophthora and plants. The pathogenic success of Phytophthora species is attributed to their diverse and rapidly evolving effector gene complements, targeting various host proteins and cellular processes. Future strategies for combating Phytophthora diseases include genome editing using CRISPR/Cas-9 technology to enhance plant immunity and the identification of non-race-specific resistance sources for broad-spectrum protection. In essence, a comprehensive understanding of Phytophthora-plant interactions at the molecular level is imperative for devising effective strategies to mitigate their impact on global agriculture.

Rhizobial elicitor molecule signaling muskmelon defense against gummy stem blight disease involving innate immune response

The crude oligosaccharide (CO) from plant growth-promoting fungus, Talaromyces verruculosum (AB2 strain) was isolated from the muskmelon rhizospheric soil in this study. Various concentrations of CO elicitor was utilized for seed treatment to muskmelon at varying time intervals to evaluate its plant growth promotion and disease protection ability against gummy stem blight disease, which is caused by Stagonosporopsis cucurbitacearum (DBTNP-2 strain). A maximum of 92% of germination and seedling vigor of 2439.76 was recorded at 6 h under in vitro conditions, after CO-pre-treated plants with 4 mgml−1. Similarly, when compared to the control, the CO-treated seed (4 mgml−1) exhibited increased vegetative growth parameters under greenhouse conditions after 6 h. In the studies of disease protection, a significant 80.88% protection from disease was noticed in plants pre-treated with CO (4 mgml−1) after 6 h. The protection thus obtained was systemic and needed a minimal of five days to achieve maximum resistance and thereafter, this protection remained stable at all time periods. An early elevated hypersensitive reaction and the defense related cellular components such as lignin, callose, H2O2 and phenol deposition, were noticed in comparison with the unprocessed control plants. Furthermore, when compared to pathogen or water control, a significant up-regulation of defense-related PAL, POX, PPO and LOX enzymes was found in the plants, which were pre-treated with CO, either with or without pathogen infection. The present research directly evidences that when confronted with the pathogen infection, the CO-treated muskmelon plants promote plant growth and trigger the resistance through the morphological, histological and biochemical defense mechanisms.

Expression of EPL1 from Trichoderma atroviride in Arabidopsis Confers Resistance to Bacterial and Fungal Pathogens.

During plant interaction with beneficial microorganisms, fungi secrete a battery of elicitors that trigger plant defenses against pathogenic microorganisms. Among the elicitor molecules secreted by Trichoderma are cerato-platanin proteins, such as EPL1, from Trichoderma atroviride. In this study, Arabidopsis thaliana plants that express the TaEPL1 gene were challenged with phytopathogens to evaluate whether expression of EPL1 confers increased resistance to the bacterial pathogen Pseudomonas syringae and the necrotrophic fungus Botrytis cinerea. Infection assays showed that Arabidopsis EPL1-2, EPL1-3, EPL1-4 expressing lines were more resistant to both pathogens in comparison to WT plants. After Pseudomonas syringae infection, there were reduced disease symptoms (e.g., small chlorotic spots) and low bacterial titers in the three 35S::TaEPL1 expression lines. Similarly; 35S::TaEPL1 expression lines were more resistant to Botrytis cinerea infection, showing smaller lesion size in comparison to WT. Interestingly, an increase in ROS levels was detected in 35S::TaEPL1 expression lines when compared to WT. A higher expression of SA- and JA-response genes occurred in the 35S::TaEPL1 lines, which could explain the resistance of these EPL1 expression lines to both pathogens. We propose that EPL1 is an excellent elicitor, which can be used to generate crops with improved resistance to broad-spectrum diseases.

Biosynthesis of Betalains Elicited by Methyl Jasmonate in Two Species of Alternanthera Genus: Antagonistic Regulations Result in Increase of Pigments.

Natural pigments are components very important in the dye industry. The betalains are pigments found in plants from Caryophyllales order and are relevant in the food manufacturing. The main source of betalains is beetroot, which has unfavorable aftertaste. Therefore, the demand for alternative species producing betalains has increased. Elicitor molecules such as methyl jasmonate (MeJA) induce metabolic reprogramming acting in the biosynthesis of specialized metabolites and can enhance pigment concentrations. Here, we used this strategy to identify if treatment with MeJA at 100µM can promote the accumulation of betalains and other bioactive compounds in Alternanthera philoxeroides and Alternanthera sessilis. We performed the gene expression, concentration of betalains, phenols, flavonoids, amino acids (phenylalanine and tyrosine), and antioxidant activity. The results showed that MeJA treatment increased betalains and other bioactive compounds in the two Alternanthera species but A. sessilis had a better performance. One key factor in this pathway is related to the phenylalanine and tyrosine concentration. However, the species have distinct metabolic regulation: in A. philoxeroides, high concentrations of betalain pigments increase the tyrosine concentration and gene expression (include ADH) under MeJA and in A. sessilis, high concentrations of betalain pigments reduce the gene expression and tyrosine concentration after 2days under MeJA. This study brings new questions about betalain biosynthesis and sheds light on the evolution of this pathway in Caryophyllales.

Chickpea pathogen-resistance-rating correlates with responsiveness to an immune elicitor protein from Phytophthora medicaginis

Identifying elicitors of plant defence from soilborne plant pathogens can provide valuable knowledge about plant-microbe interactions and can be used as an efficient screening tool in breeding programs to identify pathogen resistant genotypes. Phytophthora medicaginis causes Phytophthora Root Rot (PRR) in a range of Fabaceae hosts including soybean and chickpea. The P. medicaginis:soybean pathosystem has been well studied and qualitative plant resistance loci identified, however less is known concerning the interaction with chickpea and only quantitative resistance has been identified to date. We hypothesized that P. medicaginis encodes elicitors that are perceived by chickpea and that the responsiveness of different genotypes to the elicitor(s) would vary with disease resistance. Using sequential purification, we successfully isolated proteinaceous fractions that contained elicitor molecule(s) from the mycelium of Phytophthora medicaginis but not from the culture supernatant. We were able to purify a ∼22 kDa protein from these fractions that induced three classical plant markers for elicitor perception: an average of 2.5x more ethylene than control treatment, deposition of callose, and an increase of 2.1x in phenylalanine ammonia-lyase activity. PmEip1 perception was found to elicit strong responses in other Fabaceae hosts, and that its activity in chickpea plants varied with the degree of PRR susceptibility whereby chickpea varieties with higher levels of PRR resistance were more responsive to PmEip1 than susceptible varieties. Using tandem mass spectrometry, we found that PmEip1 shared 87.6% homology to a glyceraldehyde-3-phosphate dehydrogenase from Phytophthora cactorum. Therefore, P. medicaginis produces an elicitor protein that is perceived by chickpea. This elicitor protein could be used as a means of screening for resistant genotypes in future chickpea breeding programs.

Viewpoint of Chitosan Application in Grapevine for Abiotic Stress/Disease Management towards More Resilient Viticulture Practices

Chitosan is a biopolymer with various favorable properties (biotic/abiotic stress mitigation, qualitative improvement, bio-fertilizer, bio-stimulant and postharvest management) to meet multiple agricultural objectives. Grapevine is an important crop and has an enormous impact on the world’s economy due to its derived products, notably the different wine styles. In viticulture, chitosan application made significant developments towards higher contents of beneficial metabolites in grape berries as well as stress and postharvest management during recent decades, although the reports are limited. Recent investigations by our group demonstrated chitosan as a potential elicitor molecule at a molecular level and opened the possibility to use chitosan for trunk disease management; moreover, there are not yet any methods to combat trunk diseases in grapevine. The present viewpoint aimed to summarize the different aspects of chitosan application in grapevine in facilitating the development of inclusive and more integrated sanitary viticulture practices in a sustainable manner.

Protective and Curative Activities of Paenibacillus polymyxa against Zucchini yellow mosaic virus Infestation in Squash Plants.

Simple SummaryZucchini yellow mosaic virus (ZYMV) is one of the most prevalent plant viruses and represents a great challenge for crop production sustainability and human food supplementation. Conventional approaches to disease control depend on the heavy application of hazardous chemicals, which implies severe environmental, animal, and human health challenges. Using natural and microbial products represents a promising tool for sustainable and eco-friendly agricultural applications. The foliar application of the rhizobacteria Paenibacillus polymyxa strain SZYM revealed significant enhancements in squash growth parameters and enzyme production when compared to the non-treated plants. On the other hand, there was also a significant decrease in ZYMV accumulation, accompanied with a significant increase in the transcriptional levels of defense-related genes on plants inoculated with P. polymyxa. Additionally, a significant decrease in non-enzymatic oxidative stress markers was observed, as well as a considerable increase in reactive oxygen species scavenging enzymes. The present study showed that the P. polymyxa strain SZYM could be considered a promising rhizobacterium for enhancing plant growth and defense, and consequently a possible biocontrol agent of plant viral infections.The use of microbial products as natural biocontrol agents to increase a plant’s systemic resistance to viral infections is a promising way to make agriculture more sustainable and less harmful to the environment. The rhizobacterium Paenibacillus polymyxa has been shown to have strong biocontrol action against plant diseases, but its antiviral activity has been little investigated. Here, the efficiency of the culture filtrate of the P. polymyxa strain SZYM (Acc# ON149452) to protect squash (Cucurbita pepo L.) plants against a Zucchini yellow mosaic virus (ZYMV, Acc# ON159933) infection was evaluated. Under greenhouse conditions, the foliar application of the culture filtrate of SZYM either in protective or curative treatment conditions enhanced squash growth, reduced disease severity, and decreased ZYMV accumulation levels in the treated plants when compared to the non-treated plants. The protective treatment group exhibited the highest inhibitory effect (80%), with significant increases in their total soluble carbohydrates, total soluble protein content, ascorbic acid content, and free radical scavenging activity. Furthermore, a considerable increase in the activities of reactive oxygen species scavenging enzymes (superoxide dismutase, polyphenol oxidase, and peroxidase) were also found. In addition, the induction of systemic resistance with a significant elevation in the transcriptional levels of polyphenolic pathway genes (CHS, PAL, and C3H) and pathogenesis-related genes (PR-1 and PR-3) was observed. Out of the 14 detected compounds in the GC–MS analysis, propanoic acid, benzenedicarboxylic acid, tetradecanoic acid, and their derivatives, as well as pyrrolo [1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl) were the primary ingredient compounds in the ethyl acetate extract of the SZYM-culture filtrate. Such compounds may act as elicitor molecules that induce systemic resistance against viral infection. Consequently, P. polymyxa can be considered a powerful plant growth-promoting bacterium (PGPB) in agricultural applications as well as a source of bioactive compounds for sustainable disease management. As far as we know, this is the first time that P. polymyxa has been shown to fight viruses in plants.

Potassium salt of active phosphorous (PSAP); An innovative bioactive p and k fertilizer cum elicitor molecule in improving growth, yield, quality and climate resilience of crop plants

Potassium salt of active phosphorous (PSAP); An innovative bioactive p and k fertilizer cum elicitor molecule in improving growth, yield, quality and climate resilience of crop plants

Pathogens and Elicitors Induce Local and Systemic Changes in Triacylglycerol Metabolism in Roots and in Leaves of Arabidopsis thaliana.

Simple SummaryAbiotic and biotic stress conditions result in profound changes in plant lipid metabolism. Vegetable oil consists of triacylglycerols, which are important energy and carbon storage compounds in seeds of various plant species. These compounds are also present in vegetative tissue, and levels have been reported to increase with different abiotic stresses in leaves. This work shows that triacylglycerols accumulate in roots and in distal, non-treated leaves upon treatment with a fungal pathogen or lipopolysaccharide (a common bacterial-derived elicitor in animals and plants). Treatment of leaves with a bacterial pathogen or a bacterial effector molecule results in triacylglycerol accumulation in leaves, but not systemically in roots. These results suggest that elicitor molecules are sufficient to induce an increase in triacylglycerol levels, and that unidirectional long-distance signaling from roots to leaves is involved in pathogen and elicitor-induced triacylglycerol accumulation.Interaction of plants with the environment affects lipid metabolism. Changes in the pattern of phospholipids have been reported in response to abiotic stress, particularly accumulation of triacylglycerols, but less is known about the alteration of lipid metabolism in response to biotic stress and leaves have been more intensively studied than roots. This work investigates the levels of lipids in roots as well as leaves of Arabidopsis thaliana in response to pathogens and elicitor molecules by UPLC-TOF-MS. Triacylglycerol levels increased in roots and systemically in leaves upon treatment of roots with the fungus Verticillium longisporum. Upon spray infection of leaves with the bacterial pathogen Pseudomonas syringae, triacylglycerols accumulated locally in leaves but not in roots. Treatment of roots with a bacterial lipopolysaccharide elicitor induced a strong triacylglycerol accumulation in roots and leaves. Induction of the expression of the bacterial effector AVRRPM1 resulted in a dramatic increase of triacylglycerol levels in leaves, indicating that elicitor molecules are sufficient to induce accumulation of triacylglycerols. These results give insight into local and systemic changes to lipid metabolism in roots and leaves in response to biotic stresses.

Methyl jasmonate‐induced resistance to Delia platura (Diptera: Anthomyiidae) in Lupinus mutabilis

Andean lupin (Lupinus mutabilis Sweet) is an important leguminous crop from South America with a high protein content. In Ecuador, lupin yields are severely affected by the infestation of Delia platura larvae on germinating seeds. The application of elicitor molecules with activity against herbivorous insects to control D. platura infestation constitutes an unexplored and promising alternative for chemical insecticides. In this study, methyl jasmonate (MeJA), hexanoic acid, menadione sodium bisulfite, and DL-β-aminobutyric acid were evaluated for their ability to induce resistance against D. platura in three commercial lupin cultivars. Only seeds pretreated with MeJA significantly impaired insect performance during choice and no-choice assays. Additionally, fitness indicators such as seed germination and growth were not affected by MeJA treatment. To investigate the molecular mechanisms behind the MeJA-mediated resistance, RT-qPCR assays were performed. First, RT-qPCR reference genes were validated, showing that LmUBC was the most stable reference gene. Next, expression analysis over time revealed that MeJA application up-regulated the activity of the jasmonic acid biosynthetic genes LmLOX2 and LmAOS, together with other jasmonate-related defense genes, such as LmTPS1, LmTPS4, LmPI2, LmMBL, LmL/ODC, LmCSD1, and LmPOD. This study indicates that MeJA can be used as an environmentally friendly elicitor molecule to protect Andean lupin from D. platura attack without fitness cost. MeJA application induces plant defense responses to insects in Andean lupin that may be modulated by the onset of terpenoid biosynthesis, proteinase inhibitors, lectins, polyamines, and antioxidative enzymes. © 2021 Society of Chemical Industry.

Internalization and induction of defense responses in tobacco by harpinPss conjugated gold nanoparticles as a foliar spray

Controlled and targeted delivery of elicitor molecules with improved bioavailability is required to treat plant diseases. Here we reported stable, reproducible, and nano-sized (20–22 nm) negatively (H-AuNPs) and positively (H-CAuNPs) charged harpin adsorbed nanoparticles to induce defense responses in tobacco. The foliar application of NPs facilitated their entry possibly through epidermal stomata accumulated in the apoplast and symplast eliciting the hypersensitive response (HR) with the up-regulation of pathogenesis-related gene transcripts (PR-1, PR-2, PR-3, chitinase, HSR203, and HR specific marker gene ‘HIN1’) in 6 h. Immunogold labeling of harpinPss revealed its internalization (symplast & apoplast) and correlated with the induction of defense responses. Studies with fluorescently labeled NPs demonstrated the uptake and distribution within the leaf. Transmission electron microscopy observations revealed the internalization of H-CAuNPs and long-distance transport, eliciting systemic acquired resistance. Our observation holds promise in effectively minimizing the concentration of harpin for field application.

Bacillus licheniformis strain POT1 mediated polyphenol biosynthetic pathways genes activation and systemic resistance in potato plants against Alfalfa mosaic virus

Alfalfa mosaic virus (AMV) is a worldwide distributed virus that has a very wide host range and causes significant crop losses of many economically important crops, including potato (Solanum tuberosum L.). In this study, the antiviral activity of Bacillus licheniformis strain POT1 against AMV on potato plants was evaluated. The dual foliar application of culture filtrate (CF), 24 h before and after AMV-inoculation, was the most effective treatment that showed 86.79% reduction of the viral accumulation level and improvement of different growth parameters. Moreover, HPLC analysis showed that a 20 polyphenolic compound was accumulated with a total amount of 7,218.86 and 1606.49 mg/kg in POT1-treated and non-treated plants, respectively. Additionally, the transcriptional analysis of thirteen genes controlling the phenylpropanoid, chlorogenic acid and flavonoid biosynthetic pathways revealed that most of the studied genes were induced after POT1 treatments. The stronger expression level of F3H, the key enzyme in flavonoid biosynthesis in plants, (588.133-fold) and AN2, anthocyanin 2 transcription factor, (97.005-fold) suggested that the accumulation flavonoid, especially anthocyanin, might play significant roles in plant defense against viral infection. Gas chromatography-mass spectrometry (GC-MS) analysis showed that pyrrolo[1,2-a]pyrazine-1,4-dione is the major compound in CF ethyl acetate extract, that is suggesting it acts as elicitor molecules for induction of systemic acquired resistance in potato plants. To our knowledge, this is the first study of biological control of AMV mediated by PGPR in potato plants.

Advances in the Xoo-rice pathosystem interaction and its exploitation in disease management

Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the devastating diseases of rice worldwide. The pathogen reported to cause 70% crop loss in some of the susceptible genotypes under disease favoring environments, viz., temperature ranging between 25 to 34°C and relative humidity more than 70%. In Xoo, about 245 genes govern the pathogenicity and host specificity. The hypersensitive response and pathogenicity (hrp) genes responsible for disease occurrence were clustered in the pathogenicity island of 31.3 Kb. The protein secreted through type three secretory system and type one secretory system mediates infection and establishment of the pathogen inside the host. However, elicitor molecules from Xoo triggered the resistant response in rice against the pathogen. An array of resistant genes (R genes) was known to be invoked by the host to combat the bacterial infection. To date, of the 45 Xa genes in rice, nine were cloned and characterized. The evolution of new races has made the task of developing resistant rice genotypes more challenging as it demands a comprehensive breeding strategy involving the best use of R genes from the existing gene pool. Thus, to combat the infection from the existing races and to slow down the emergence of new Xoo races, pyramiding two or more R genes was found to be effective against bacterial blight disease. In India, the successfully commercialized example includes the development of rice genotypes, viz., Improved Pusa Basmati- 1, Improved Samba Mahsuri, PR106, Type 3 Basmati, and Mahsuri with selected R genes, viz., xa5, Xa4, xa13 and Xa21 against bacterial blight resistance. This review primarily portray Xoo-rice interactions and provides opportunities for its effective management through sustainable technologies.

Bacillus velezensis PEA1 Inhibits Fusarium oxysporum Growth and Induces Systemic Resistance to Cucumber Mosaic Virus

Bacillus velezensis manifests robust biocontrol activity against fungal plant pathogens; however, its antiviral activity has rarely been investigated. Bacillus velezensis strain PEA1 was isolated, characterized, and evaluated for antifungal and antiviral activities against Fusarium oxysporum MT270445 and cucumber mosaic virus (CMV) MN594112. Our findings proved that strain PEA1 had intense antagonist activity against F.oxysporum. Under greenhouse conditions, the antiviral activities (protective, curative, and inactivation) of PEA1-culture filtrate (CF) on Datura stramonium plants were assayed, using a half-leaf method. The inactivation treatment exhibited the highest inhibition rate (97.56%) and the most considerable reduction of CMV-CP accumulation levels (2.1-fold) in PEA1-CF-treated plants when compared with untreated plants (26.9-fold). Furthermore, PEA1-CF induced systemic resistance with significantly elevated transcriptional levels of PAL, CHS, HQT, PR-1, and POD genes in D. stramonium leaves after all treatments. Gas chromatography‒mass spectrometry analysis showed that pyrrolo[1,2-a]pyrazine-1,4-dione is the main compound in the PEA1-CF ethyl acetate extract, which may act as an elicitor molecule that induces plant systemic resistance and inhibits both fungal growth and viral replication. Consequently, B. velezensis can be considered as a potential source for the production of bioactive compounds for the management of plant diseases. To our knowledge, this is the first report of the antiviral activity of B. velezensis against plant viral infection.

Induced tolerance to abiotic and biotic stresses of broccoli and Arabidopsis after treatment with elicitor molecules

The plant hormones salicylic acid (SA) and jasmonic acid (JA) regulate defense mechanisms capable of overcoming different plant stress conditions and constitute distinct but interconnected signaling pathways. Interestingly, several other molecules are reported to trigger stress-specific defense responses to biotic and abiotic stresses. In this study, we investigated the effect of 14 elicitors against diverse but pivotal types of abiotic (drought) and biotic (the chewing insect Ascia monuste, the hemibiotrophic bacterium Pseudomonas syringae DC 3000 and the necrotrophic fungus Alternaria alternata) stresses on broccoli and Arabidopsis. Among the main findings, broccoli pre-treated with SA and chitosan showed the highest drought stress recovery in a dose-dependent manner. Several molecules led to increased drought tolerance over a period of three weeks. The enhanced drought tolerance after triggering the SA pathway was associated with stomata control. Moreover, methyl jasmonate (MeJA) reduced A. monuste insect development and plant damage, but unexpectedly, other elicitors increased both parameters. GUS reporter assays indicated expression of the SA-dependent PR1 gene in plants treated with nine elicitors, whereas the JA-dependent LOX2 gene was only expressed upon MeJA treatment. Overall, elicitors capable of tackling drought and biotrophic pathogens mainly triggered the SA pathway, but adversely also induced systemic susceptibility to chewing insects. These findings provide directions for potential future in-depth characterization and utilization of elicitors and induced resistance in plant protection.

Proteomic analysis reveals the mechanisms involved in the enhanced biocontrol efficacy of Rhodotorula mucilaginosa induced by chitosan

The biocontrol efficacy of the yeast, Rhodotorula mucilaginosa against postharvest diseases of strawberries can be significantly enhanced by culturing the yeast in a medium containing chitosan. The molecular mechanisms involved in the enhanced biocontrol efficacy of R. mucilaginosa, however, have not been comprehensively explored. Results of the present study indicate that the biocontrol efficacy of the yeast against gray mold (Botrytis cinerea) of strawberry was greatest when the yeast was cultured in a medium containing 0.5% (w:v) chitosan for 24 h before use. Proteomic and bioinformatic analyses revealed that proteins involved in growth and reproduction, energy metabolism, antioxidant response, response to abiotic stress, and degradation of pathogen cell walls were all up-regulated by chitosan resulting in the enhanced antagonistic activity of R. mucilaginosa against B. cinerea. The decrease in ROS accumulation in R. mucilaginosa cultured in a medium containing chitosan was in agreement with the increased abundance of proteins related to antioxidant defense. Key differentially expressed proteins (DEPs) were identified and 12 randomly-selected DEPs were validated by parallel reaction monitoring. The present results provide a theoretical reference for further study of the molecular mechanisms involved in the improvement of biocontrol efficacy of antagonistic yeast by elicitor molecules and also provide a novel approach for improving biological control of postharvest diseases.

Elicitor and Receptor Molecules: Orchestrators of Plant Defense and Immunity.

Pathogen-associated molecular patterns (PAMPs), microbe-associated molecular patterns (MAMPs), herbivore-associated molecular patterns (HAMPs), and damage-associated molecular patterns (DAMPs) are molecules produced by microorganisms and insects in the event of infection, microbial priming, and insect predation. These molecules are then recognized by receptor molecules on or within the plant, which activates the defense signaling pathways, resulting in plant’s ability to overcome pathogenic invasion, induce systemic resistance, and protect against insect predation and damage. These small molecular motifs are conserved in all organisms. Fungi, bacteria, and insects have their own specific molecular patterns that induce defenses in plants. Most of the molecular patterns are either present as part of the pathogen’s structure or exudates (in bacteria and fungi), or insect saliva and honeydew. Since biotic stresses such as pathogens and insects can impair crop yield and production, understanding the interaction between these organisms and the host via the elicitor–receptor interaction is essential to equip us with the knowledge necessary to design durable resistance in plants. In addition, it is also important to look into the role played by beneficial microbes and synthetic elicitors in activating plants’ defense and protection against disease and predation. This review addresses receptors, elicitors, and the receptor–elicitor interactions where these components in fungi, bacteria, and insects will be elaborated, giving special emphasis to the molecules, responses, and mechanisms at play, variations between organisms where applicable, and applications and prospects.

Induction of potato systemic resistance against the potato virus Y (PVYNTN), using crude filtrates of Streptomyces spp. under greenhouse conditions

The potato virus Y (PVY) is considered one of the most important viruses in terms of both economical and biological impact. Potential of using three different Streptomyces spp. crude filtrates (SCF) to induce of resistance against tuber necrotic strain of potato virus Y (PVYNTN) in four potato cultivars namely, Spunta, Nicola, Selatar, and Diamant, were evaluated. Foliar spraying of Streptomyces netropsis DSM 40093 (SCF7), S. ambofaciens (SCF11) and S. actuosus (SCF20), applied separately on potato cultivated in pots, showed various inhibitory activities against PVYNTN infection in all the potato cultivars. SCF20 was the most effective one, as expressed by (100%) reduction of apical necrosis symptoms on potato cv. Spunta, Nicola, and Diamant leaves under greenhouse conditions. Application was done 7 days before virus inoculation with PVYNTN (DBVI) and 7 days after inoculation (DAVI). The concentration of PVYNTN in treatments was significantly reduced than in the untreated PVYNTN infected plants as detected by DAS-ELISA (expressed by decreasing in OD value). Expression of PR-1b gene was detected 21 (DAVI) in all SCF11-treated cultivars but was not expressed in healthy and infected control plants. Gas chromatography-mass spectrometry (GC-MS) analysis of S. actuosus (SCF20) ethyl acetate extract revealed the majority of fatty acids (FAs) and their derivatives, Citroflex A, Hexanoic acid, anhydride, Hexadecanoic acid, Hexadecanoic acid, ethyl ester, and Diisooctyl phthalate which suggested to act as elicitor molecules for induction of systemic acquired resistance (SAR). Overall, the application of culture filtrates of Streptomyces has the potentiality to be used as inducer against PVYNTN infection.

Pattern-Triggered Oxidative Burst and Seedling Growth Inhibition Assays in Arabidopsis thaliana.

Plants have evolved a robust immune system to perceive pathogens and protect against disease. This paper describes two assays that can be used to measure the strength of immune activation in Arabidopsis thaliana following treatment with elicitor molecules. Presented first is a method for capturing the rapidly-induced and dynamic oxidative burst, which can be monitored using a luminol-based assay. Presented second is a method describing how to measure immune-induced inhibition of seedling growth. These protocols are fast and reliable, do not require specialized training or equipment, and are widely used to understand the genetic basis of plant immunity.

Identification of Candidate Ergosterol-Responsive Proteins Associated with the Plasma Membrane of Arabidopsis thaliana.

The impact of fungal diseases on crop production negatively reflects on sustainable food production and overall economic health. Ergosterol is the major sterol component in fungal membranes and regarded as a general elicitor or microbe-associated molecular pattern (MAMP) molecule. Although plant responses to ergosterol have been reported, the perception mechanism is still unknown. Here, Arabidopsis thaliana protein fractions were used to identify those differentially regulated following ergosterol treatment; additionally, they were subjected to affinity-based chromatography enrichment strategies to capture and categorize ergosterol-interacting candidate proteins using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Mature plants were treated with 250 nM ergosterol over a 24 h period, and plasma membrane-associated fractions were isolated. In addition, ergosterol was immobilized on two different affinity-based systems to capture interacting proteins/complexes. This resulted in the identification of defense-related proteins such as chitin elicitor receptor kinase (CERK), non-race specific disease resistance/harpin-induced (NDR1/HIN1)-like protein, Ras-related proteins, aquaporins, remorin protein, leucine-rich repeat (LRR)- receptor like kinases (RLKs), G-type lectin S-receptor-like serine/threonine-protein kinase (GsSRK), and glycosylphosphatidylinositol (GPI)-anchored protein. Furthermore, the results elucidated unknown signaling responses to this MAMP, including endocytosis, and other similarities to those previously reported for bacterial flagellin, lipopolysaccharides, and fungal chitin.