Induce Plant Defense Responses Research Articles

Mitigation strategy of saline stress in Fragaria vesca using natural and synthetic brassinosteroids as biostimulants.

Bassinosteroids (BRs) can induce plant defence responses and promote plant growth. In this work, we evaluated the effect of a natural (EP24) and a synthetic (BB16) brassinosteroid on strawberry (Fragaria vesca ) plants exposed to saline stress. Treated plants showed higher shoot dry weight and root growth compared to untreated control plants. In BR-treated plants, crown diameters increased 66% and 40%, leaf area 148% and 112%, relative water content in leaves 84% and 61%, and SPAD values 24% and 26%, in response to BB16 and EP24, respectively. A marked stomatal closure, increased leaflet lignification, and a decrease in cortex thickness, root diameter and stele radius were also observed in treated plants. Treatments also reduces stress-induced damage, as plants showed a 34% decrease in malondialdehyde content and a lower proline content compared to control plants. A 22% and 15% increase in ascorbate peroxidase and total phenolic compound activities was observed in response to BB16, and a 24% increase in total flavonoid compound in response to both BRs, under stress conditions. These results allow us to propose the use of BRs as an environmentally safe crop management strategy to overcome salinity situations that severely affect crop yield.

The Efficacy of Orange Terpene and Bacillus mycoides Strain BM103 on the Control of Periwinkle Leaf Yellowing Phytoplasma.

Phytoplasmas are obligate phytopathogenic bacteria belonging to the class Mollicutes. The pathogens, transmitted by insect vectors, associated with hundreds of plant diseases worldwide. Due to the regulation on banning use of antibiotics and limited efficacy of the traditional disease management manners, an eco-friendly alternative is needed. Given that terpene and probiotics have antibiotic activity and the ability to induce systemic resistance, in this study, the effectiveness of orange terpene and a Bacillus mycoides strain, BM103, was evaluated in periwinkle plants infected with periwinkle leaf yellowing (PLY) phytoplasma derived from a shoot-tip tissue culture system. Weekly drenching of 1,000 ppm diluted orange terpene emulsion or pre-activated strain BM103 liquid culture dilution exhibited the ability to inhibit PLY phytoplasma accumulation. The expression of the genes associated with plant defense response and flower development was upregulated after treatment. Moreover, pre-treatment of orange terpene or strain BM103 delayed PLY infection via cleft-grafting inoculation. While orange terpene did not suppress the symptoms, strain BM103 did result in a milder symptom expression that might partially attribute to its plant growth-promoting characteristics. Additionally, the pre-activation of strain BM103 may contribute to its efficacy. Taken together, this research indicates that orange terpene and B. mycoides BM103, with the ability to rapidly induce plant defense responses, could potentially be developed into biological control materials as preventive agents or biofertilizers.

Potential of different species of actinobacteria in the management of Meloidogyne javanica.

Root-knot nematodes (RKN) are one of the most harmful soil-borne plant pathogens in the world. Actinobacteria are known phytopathogen control agents. The aim of this study was to select soil actinobacteria with control potential against the RKN (Meloidogyne javanica) in tomato plants and to determine mechanisms of action. Ten isolates were tested and a significant reduction was observed in the number of M. javanica eggs, and galls 46days after infestation with the nematode. The results could be explained by the combination of different mechanisms including parasitism and induction of plant defense response. The M. javanica eggs were parasited by all isolates tested. Some isolates reduced the penetration of juveniles into the roots. Other isolates using the split-root method were able to induce systemic defenses in tomato plants. The 4L isolate was selected for analysis of the expression of the plant defense genes TomLoxA, ACCO, PR1, and RBOH1. In plants treated with 4L isolate and M. javanica, there was a significant increase in the number of TomLoxA and ACCO gene transcripts. In plants treated only with M. javanica, only the expression of the RBOH1 and PR1 genes was induced in the first hours after infection. The isolates were identified using 16S rRNA gene sequencing as Streptomyces sp. (1A, 3F, 4L, 6O, 8S, 9T, and 10U), Kribbella sp. (5N), Kitasatospora sp. (2AE), and Lentzea sp. (7P). The efficacy of isolates from the Kitasatospora, Kribbella, and Lentzea genera was reported for the first time, and the efficacy of Streptomyces genus isolates for controlling M. javanica was confirmed. All the isolates tested in this study were efficient against RKN. This study provides the opportunity to investigate bacterial genera that have not yet been explored in the control of M. javanica in tomatoes and other crops.

Trichoderma harzianum Cellulase Gene thph2 Affects Trichoderma Root Colonization and Induces Resistance to Southern Leaf Blight in Maize.

Trichoderma, widely distributed all over the world, is commonly found in soil and root ecosystems. It is a group comprising beneficial fungi that improve plant disease resistance and promote plant growth. Studies have shown that Trichoderma cellulases can also improve plant disease resistance. Based on previous studies, we reported that a C6 zinc finger protein (Thc6) regulates two cellulase genes, thph1 and thph2, to induce ISR responses in plants. Therefore, in this study, we focused on the role of thph2 in the colonization of maize roots by T. harzianum and the induction of systemic resistance against southern leaf blight. The results showed that thph2 had a positive regulatory effect on the Trichoderma colonization of maize roots. After the root was treated with Trichoderma, the leaf defense genes AOS, LOX5, HPL, and OPR1 were expressed to resist the attack of Cochliobolus heterostrophus. The pure Thph2 protein also resulted in a similar induction activity of the AOS, LOX5, HPL, and OPR1 expression in maize roots, further demonstrating that thph2 can induce plant defense responses and that signal transduction occurs mainly through the JA signaling pathway.

Exogenous salicylic acid induces defense responses in tea plants against Toxoptera aurantii (Hemiptera: Aphididae).

Toxoptera aurantii is one of the most destructive pests, threatening the yield and quality of tea plantations. The salicylic acid (SA)-mediated signaling pathway is vital for the induction of plant defense responses; however, its role in tea plant resistance to T. aurantii remains unclear. Thus, this study used and electrical penetration graph and monitoring of population dynamics to evaluate the effects of exogenous SA application on T. aurantii feeding behavior and population growth in tea seedlings. Moreover, the effects of SA treatment on the activities of defense-related enzymes were analyzed. Probe counts and the duration of xylem sap ingestion were significantly higher in SA-treated plants than those in the control group. The total duration of passive phloem ingestion was significantly decreased in 0.5 mmol/l SA-treated plants, and the application of 0.5, 1, and 4 mmol/l SA significantly inhibited T. aurantii population growth. In addition, the activities of polyphenol oxidase, peroxidase, and superoxide dismutase were significantly increased in the 0.5 mmol/l SA-treated plants. Overall, this study demonstrates the capacity of exogenous SA to activate defense responses against T. aurantii. These results have crucial implications for understanding the mechanisms of enhanced resistance, thereby providing a sustainable approach for managing T. aurantii.

Repurposing Salicylamides to Combat Phytopathogenic Bacteria and Induce Plant Defense Responses.

Based on the research strategy of "drug repurposing", a series of derivatives and marketed drugs that containing salicylic acid skeleton were tested for their antibacterial activities against phytopathogens. Salicylic acid can not only regulate some important growth metabolism of plants, but also induce plant disease resistance. The bioassay results showed that the salicylamides exhibited excellent antibacterial activity. Especially, oxyclozanide showed the best antibacterial effect against Xanthomonas oryzae, Xanthomonas axonopodis pv. citri and Pectobacterium atroseptica with MICs of 0.78, 3.12 and 12.5 μg.mL-1, respectively. In vivo experiments with rice bacterial leaf blight had further demonstrated that oxyclozanide exhibited stronger antibacterial activity than the commercial bactericide, thiodiazole copper. Oxyclozanide could induce plant defense responses through the determination of salicylic acid content and the activities of defense-related enzymes including CAT, POD, and SOD in rice. The preliminarily antibacterial mechanism study indicated that oxyclozanide exhibited the antibacterial activity by disrupting cell integrity and reducing bacterial pathogenicity. Additionally, oxyclozanide could induce plant defense responses through the determination of salicylic acid content.

Development of multi-target dsRNAs targeting PcNLP gene family to suppress Phytophthora capsici infection in Nicotiana benthamiana

Phytophthora capsici, which causes diseases in solanaceous crops, secretes necrosis and ethylene-inducing peptide 1-like proteins (NLPs) that induce plant defense responses and leaf necrosis. In this study, we used RNA interference (RNAi) technique, a proven strategy for crop protection and gene regulation in plants, to suppress P. capsici infection through the inhibition of PcNLPs. In the RNAi mechanism, Dicer processes double-stranded RNA (dsRNA) into smaller entities known as small interfering RNAs (siRNAs). These siRNAs subsequently integrate into the RNA-induced silencing complex to form sequence-specific base pairing with complementary regions of the target mRNA. This interaction effectively initiates the degradation process of the target mRNA. We designed and synthesized dsRNAs targeting the “AIMY” and “GHRHDWE” conserved motifs of PcNLP gene family, which are predicted to be key elements for the expression of NLPs and pathogen infection. After infiltration of dsRNAs targeting the motifs and inoculation with P. capsici, we confirmed a significant suppression of P. capsici infection and downregulation of the PcNLP gene family. These findings imply that the dsRNA-mediated RNAi technique holds potential for mitigating a wide range of pathogens, while simultaneously suppressing the expression of a particular gene family using dsRNA targeting functional conserved motifs in the gene family.

Pectate Lyase from Fusarium sacchari Induces Plant Immune Responses and Contributes to Virulence.

Fusarium sacchari is one of the primary pathogens causing Pokkah Boeng disease (PBD) in sugarcane in China. Pectate lyases (PL), which play a critical role in pectin degradation and fungal virulence, have been extensively studied in major bacterial and fungal pathogens of a wide range of plant species. However, only a few PLs have been functionally investigated. In this study, we analyzed the function of the pectate lyase gene, FsPL, from F. sacchari. FsPL is a key virulence factor of F. sacchari and can induce plant cell death. FsPL also triggers the pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) response in Nicotiana benthamiana, as reflected by increases in reactive oxygen species (ROS) production, electrolyte leakage, and callose accumulation, as well as the upregulation of defense response genes. In addition, our study also found that the signal peptide of FsPL was necessary for induced cell death and PTI responses. Virus-induced gene silencing showed that FsPL-induced cell death in Nicotiana benthamiana was mediated by leucine-rich repeat (LRR) receptor-like kinases BAK1 and SOBIR1. Thus, FsPL may not only be a critical virulence factor for F. sacchari but may also induce plant defense responses. These findings provide new insights into the functions of pectate lyase in host-pathogen interactions. IMPORTANCE Pokkah Boeng disease (PBD) is one of the main diseases affecting sugarcane in China, seriously damaging sugarcane production and economic development. Therefore, it is important to clarify the pathogenic mechanisms of this disease and to provide a theoretical basis for the breeding of PBD-resistant sugarcane strains. The present study aimed to analyze the function of FsPL, a recently identified pectate lyase gene from F. sacchari. FsPL is a key virulence factor of F. sacchari that induces plant cell death. Our results provide new insights into the function of pectate lyase in host-pathogen interactions.

Seed Treatment with Calcium Carbonate Containing Bacillus amyloliquefaciens PMB05 Powder Is an Efficient Way to Control Black Rot Disease of Cabbage

Black rot disease is a serious bacterial disease that harms vegetable crops of the Brassica genus (especially cabbage plants) worldwide. The causal agent, Xanthomonas campestris pv. campestris (Xcc), is a seed-borne pathogen that primarily infects seedlings. Previous studies suggest that the bacterial strain, Bacillus amyloliquefaciens PMB05, can intensify the plant immune responses of cabbage against black rot disease and reduce disease occurrence. In plant immunity, several reactions occur during a pathogen attack, but the elevation of calcium ion concentration in plant cells is essential in the induction of plant defense responses. Therefore, this study aims to investigate whether disease control of black rot disease in cabbage plants can be improved by integrating calcium carbonate in the formulation for preparing B. amyloliquefaciens PMB05. Firstly, we found the addition of calcium carbonate in the formulation revealed to have significantly increased the cell and endospore populations of B. amyloliquefaciens PMB05 in the fermentation liquids. To increase the convenience of disease control in the field, these fermentation liquids were converted to powder form for subsequent analysis. Results revealed that the grown seedlings from seeds, mixed with PMB05 powders, significantly intensified plant immune responses and improved black rot disease control. We further compared distinct seed treatments using one PMB05 powder to evaluate its feasibility in field application. The results demonstrated that the disease control efficacy and yield of cabbage were significantly improved in the seed treatment with the powder (SD-160C2) to 56.46% and 5.91%, respectively, at 10 weeks post transplanting. Interestingly, the seed treatment combined with a calcium-containing commercial fertilizer spraying treatment did not increase the control efficacy of black rot disease, but it significantly increased the weight of cabbages after harvest. We concluded that the seed treatment with calcium carbonate-containing Bacillus amyloliquefaciens PMB05 powder is an efficient way to control black rot disease in cabbage.

Use of salicylic acid during cultivation of plants as a strategy to improve its metabolite profile and beneficial health effects

Chemical elicitors in plants during cultivation have been applied in soil, hydroponic solutions, or sprayed on the leaves to induce physiological changes and stimulate the production of bioactive compounds. Salicylic acid (SA) is a phenolic compound present in plants with multiple functions, including stimulus of plant growth and induction of plant defense responses under conditions of stress. Recently, the use of SA as elicitor has generated much interest, due to the growing number of studies demonstrating its positive effects in fruits, vegetables, and herbs on the induction of phytochemicals, mainly phenolic compounds, alkaloids, saponins, carotenoids, among others. The health benefits of plant materials treated with SA are mainly their antioxidant capacities determined by the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrilhidrazil (DPPH) assays and anti-inflammatory properties determined in vitro, as well as hypoglycemic and hypolipidemic properties and renal protection evaluated by in vivo studies. Therefore, the exogenous application of SA during cultivation of different plants could be an alternative to increase their economic value and could be the basis for designing standardized procedures in the production of bioactive compounds.

Identification of dominant taxa of sooty moulds and their impact on the leaf microbiome.

Sooty moulds are a widespread group of saprophytic ascomycetes that obtain nutrients from honeydew excreted by sap-feeding insects and coat plant tissue with mycelia. Research on sooty moulds has focused on fungal morphology and phylogeny-based taxonomy, but little research has been conducted on the community structure. In this study, the PacBio sequencing platform was used to systematically analyse the fungal and bacterial diversity of the sooty mould community on camphor trees at two sampling sites. Six dominant sooty mould genera were identified, of which three genera of Dothideomycetes were enriched only in diseased samples, while three genera of Eurotiomycetes were present in both healthy and diseased samples. Bacterial diversity and co-occurrence network analysis indicated that the sooty moulds had an effect on the leaf surface bacterial communities but not on the endophyte communities. There was a close correlation between the six dominant pathogenic groups and bacteria in the soot layer. Transcriptomic data from Cinnamomum camphora samples showed that the sooty moulds that did not penetrate plant cells not only affected plant photosynthesis but also induced plant defence responses. This study systematically studied the microbial community of sooty moulds, indicating the close relationship between sooty moulds and the bacterial communities.

Plant Disease Resistance-Related Signaling Pathways: Recent Progress and Future Prospects.

Plant-pathogen interactions induce a signal transmission series that stimulates the plant's host defense system against pathogens and this, in turn, leads to disease resistance responses. Plant innate immunity mainly includes two lines of the defense system, called pathogen-associated molecular pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). There is extensive signal exchange and recognition in the process of triggering the plant immune signaling network. Plant messenger signaling molecules, such as calcium ions, reactive oxygen species, and nitric oxide, and plant hormone signaling molecules, such as salicylic acid, jasmonic acid, and ethylene, play key roles in inducing plant defense responses. In addition, heterotrimeric G proteins, the mitogen-activated protein kinase cascade, and non-coding RNAs (ncRNAs) play important roles in regulating disease resistance and the defense signal transduction network. This paper summarizes the status and progress in plant disease resistance and disease resistance signal transduction pathway research in recent years; discusses the complexities of, and interactions among, defense signal pathways; and forecasts future research prospects to provide new ideas for the prevention and control of plant diseases.

ATP-citrate lyase B (ACLB) negatively affects cell death and resistance to Verticillium wilt

BackgroundATP-citrate lyase (ACL) plays a pivotal role in histone acetylation and aerobic glycolysis. In plant, ACL is a heteromeric enzyme composed of ACLA (45 kD) and ACLB (65 kD). So far, the function of ACL genes in cotton still remains unknown.ResultsHere, we identified three ACLA homologous sequences and two ACLB homologous in each genome/sub-genome of cotton species. Silencing ACLB in cotton led to cell death at newly-grown leaves and stem apexes. Simultaneously, in ACLB-silenced plants, transcription factors related to senescence including SGR, WRKY23 and Osl57 were observed to be activated. Further investigation showed that excessive H2O2 was accumulated, salicylic acid-dependent defense response and pathogenesis-related gene expressions were evidently enhanced in ACLB-silenced plants, implying that knockdown of ACLB genes leads to hypersensitive response-like cell death in cotton seedlings. However, as noted, serious cell death happened in newly-grown leaves and stem apexes in ACLB-silenced plants, which led to the failure of subsequent fungal pathogenicity assays. To confirm the role of ACLB gene in regulating plant immune response, the dicotyledonous model plant Arabidopsis was selected for functional verification of ACLB gene. Our results indicate the resistance to Verticillium dahliae infection in the Arabidopsis mutant aclb-2 were enhanced without causing strong cell death. Ectopic expression of GausACLB-2 in Arabidopsis weakened its resistance to V. dahliae either in Col-0 or in aclb-2 background, in which the expression level of ACLB is negatively correlated with the resistance to V. dahliae.ConclusionsThese results indicate that ACLB has a new function in negatively affecting the induction of plant defense response and cell death in cotton, which provides theoretical guidance for developing cotton varieties with resistance against Verticillium wilt.

Identification of Key Residues Essential for the Activation of Plant Immunity by Subtilisin From Bacillus velezensis LJ02

Subtilisin, a serine protease, can trigger defense responses in a wide variety of plants, both locally and systemically, to protect against pathogens. However, key residues of subtilisin to improve resistance to plant diseases remain unknown. In this study, Nicotiana benthamiana (N. benthamiana) leaves expressing subtilisin from Bacillus velezensis LJ02 were shown to improve protection against Botrytis cinerea (B. cinerea). Furthermore, the underlying mechanism that LJ02 subtilisin improved the protective effect was explored, and the direct inhibitory effect of subtilisin on B. cinerea was excluded in vitro. Subsequently, reactive oxygen species (ROS) burst and upregulation of resistance-related genes in systemic leaves of N. benthamiana further verified that subtilisin could induce systemic protection against B. cinerea. G307A/T308A and S213A/L214A/G215A subtilisin significantly reduced the ability to resist B. cinerea infection in N. benthamiana. Furthermore, the ROS content and expression levels of resistance-related genes of both mutants were significantly decreased compared with that of wild-type subtilisin. This work identified key residues essential for the activation function of subtilisin plant immunity and was crucial in inducing plant defense responses against B. cinerea.

Elicitor Activity of Curdlan and Its Potential Application in Protection of Hass Avocado Plants against Phytophthora cinnamomi Rands

Phytophthora cinnamomi causes one of the most important diseases in avocado crop and its chemical management represents 25% of the production cost per year. Induction of plant defense responses by elicitors is a promising strategy that is compatible with sustainable agriculture. This study aimed to evaluate the effect of curdlan application on the induction of defense responses in avocado plants against P. cinnamomi. The trials were conducted under greenhouse conditions, and curdlan leaf spraying was performed one day before the inoculation of the pathogen. The results showed that the application of elicitor significantly increased the protection of avocado plants against P. cinnamomi, decreasing the injury and wilting. The Curd + Phy treatment improved the defenses of plants by increasing the enzymes peroxidase (POD) and polyphenol oxidase (PPO) in the first 3 h after inoculation and increasing the enzymes superoxide dismutase (SOD) and phenylalanine ammonium lyase (PAL) 144 h after inoculation (p < 0.05). Also, chlorophyll and carotenoid content increased or remained stable in Curd + Phy treatment. Therefore, these results suggest that curdlan increases the protection against P. cinnamomi and its protection could be due to an increase in the activity of the enzymes related to the phenylpropanoid pathway as well as the effect on chlorophyll and carotenoids.

Induction of resistance in tomato against Sclerotium rolfsii by application of seaweed extract and chemical compounds

Southern blight of tomato caused by Sclerotium rolfsii is a destructive disease and the efficacy of current strategies for managing the disease is limited and alternative disease management methods are needed. Trials were conducted to assess the induction of plant defense responses in tomato by using seaweed extract (SW), mandipropamid, thiamethoxam and sulfur. Southern blight disease severity and plant growth parameters along with levels of defense related enzymes, proline and chlorophyll contents were assessed. Results showed that elicitors application significantly (P ≤ 0.01) reduced mycelial growth and disease severity along with enhancement of plant growth parameters. Application of elicitors triggered multiple antioxidant enzymatic responses including SOD, POD, CAT, proline content and chlorophyll content, which might have contributed to the enhancement of plant defense against S. rolfsii. The results suggested that elicitors could be applied along with other fungicides to reduce the usage of chemical fungicides and contribute to the development of sustainable agriculture.

Phosphorylation of an ethylene response factor by MPK3/MPK6 mediates negative feedback regulation of pathogen-induced ethylene biosynthesis in Arabidopsis

Plants under pathogen attack produce high levels of the gaseous phytohormone ethylene to induce plant defense responses via the ethylene signaling pathway. The 1-aminocyclopropane-1-carboxylate synthase (ACS) is a critical rate-limiting enzyme of ethylene biosynthesis. Transcriptional and post-translational upregulation of ACS2 and ACS6 by the mitogen-activated protein kinases MPK3 and MPK6 are previously shown to be crucial for pathogen-induced ethylene biosynthesis in Arabidopsis. Here, we report that the fungal pathogen Botrytis cinerea-induced ethylene biosynthesis in Arabidopsis is under the negative feedback regulation by ethylene signaling pathway. The ethylene response factor ERF1A is further found to act downstream of ethylene signaling to negatively regulate the B. cinerea-induced ethylene biosynthesis via indirectly suppressing the expression of ACS2 and ACS6. Interestingly, ERF1A is shown to also upregulate defensin genes directly and therefore promote Arabidopsis resistance to B. cinerea. Furthermore, ERF1A is identified to be a substrate of MPK3 and MPK6, which phosphoactivate ERF1A to enhance its functions in suppressing ethylene biosynthesis and inducing defensin gene expression. Taken together, our data reveal that ERF1A and its phosphorylation by MPK3/MPK6 not only mediate the negative-feedback regulation of the B. cinerea-induced ethylene biosynthesis, but also upregulate defensin gene expression to increase Arabidopsis resistance to B. cinerea.

N-[5-(Trifluoromethyl)pyridin-2-yl]benzenesulfonamide partially mimics methyl jasmonate without growth inhibition in Nicotiana benthamiana

Jasmonates (JAs) are phytohormones that induce plant defense responses against pathogens and herbivores. However, JAs often cause plant growth inhibition. Thus, JAs have not been practically useful for crop protection to date. In this study, we demonstrate that N-[5-(Trifluoromethyl)pyridin-2-yl]benzenesulfonamide (TPBS) can upregulate JA-inducible defense genes in Nicotiana benthamiana plants without severe growth inhibition. Using a promoter-luciferase-based high-throughput system (HTS) in Arabidopsis thaliana seedlings, TPBS was found to be an agonist of methyl jasmonate (MeJA)-dependent responses, although TPBS has no structural similarity to MeJA. MeJA strongly upregulates the expression of many secondary metabolite-related genes involved in five major secondary metabolic pathways: the alkaloid, terpenoid, phenylpropanoid, flavonoid, and anthocyanin pathways. TPBS application significantly upregulated only some of these genes in the roots, mainly those involved in the alkaloid biosynthesis pathways. The biological activity of TPBS was tested according to its ability to increase the accumulation of nicotine, a well-known JA-inducible alkaloid involved in defense responses. TPBS led to accumulation of nicotine as much as MeJA in N. benthamiana leaves. We found that 10 μM TPBS led to nicotine accumulation (9.7-fold) without growth inhibition (104%), indicating that TPBS can uncouple defense responses from growth inhibition. These features make TPBS a strong candidate for use in crop protection, as demonstrated by increased nicotine content in tobacco.

Apolygus lucorum-induced resistance in Vitis vinifera L. elicits changes at the phenotypic, physiological, and biochemical levels

The infestation of the pest Apolygus lucorum (Meyer-Dür, 1843) induced changes in Vitis vinifera L. ‘Cabernet Sauvignon’ at the growth, physiological, and biochemical levels, which were recorded in this study. Continuous infestation by A. lucorum for > 4 d significantly affected plant height and leaf width, although there were no effects when infestation was for ≤ 4 d. Over the long term, A. lucorum mortality increased and their average survival time decreased. A. lucorum-based injury induced plant defense responses, and a spike in defense enzymes was observed. Additionally, infestation induced significant changes in protease inhibitor and secondary metabolite levels in the grape leaves. After A. lucorum infestation, total sugar, protein, and chlorophyll in the leaf decreased significantly. Puncture injury generally induced a milder response compared with A. lucorum infestation. In summary, A. lucorum infestation induced resistance in Cabernet Sauvignon by activating various physiological and biochemical defense responses. In addition to providing new insights into the coevolution of plants and insects, the results presented in this study may lead to the development of an effective, innovative, and environmentally friendly pest control method.

Postharvest Fumigation of (E)-2-Hexenal on Kiwifruit (Actinidia chinensis cv. ‘Haegeum’) Enhances Resistance to Botrytis cinerea

(E)-2-Hexenal is a reactive electrophile species released by green plants upon herbivory or pathogenic infection and induces various defense responses. In this study, (E)-2-hexenal was used as a natural alternative to artificial fumigants to prevent postharvest pathogenic infection of the ‘Haegeum’ kiwifruit (Actinidia chinensis). Integrated transcriptome-metabolome analyses were performed to investigate its effect on the induction of plant defense responses. When kiwifruit was fumigated with 100 μmol L-1 (E)-2-hexenal for 24 h at 20 °C and then inoculated with fungal pathogen Botrytis cinerea, the disease severity, as assessed by necrotic lesion size and B. cinerea biomass, was reduced compared to the control, distilled water-treated fruit. (E)-2-Hexenal treatment also led to upregulated expression of genes encoding pattern recognition receptors, signal transducer proteins, and pathogenesis-related proteins, including chitinase. Furthermore, treatment led to increased jasmonic acid and flavonoid biosynthesis. (E)-2-Hexenal fumigation therefore enhanced the resistance of kiwifruit to B. cinerea infection, presumably by facilitating the signaling network from pathogen recognition to defense gene expression and enabling the accumulation of secondary metabolites, such as flavonoids. The present study not only suggests an optimal concentration of (E)-2-hexenal fumigation for controlling postharvest disease of kiwifruit, but also broadens our understanding of the underlying molecular mechanism by which (E)-2-hexenal enhances plant resistance.