Induced Disease Resistance Research Articles

Epsilon-poly-l-lysine increases disease resistance of citrus against postharvest green mold by activating amino acid metabolism and phenolic compounds biosynthesis

AbstractAs a famous fruit worldwide, citrus is susceptible to green mold caused by Penicillium digitatum, which causes large economic losses every year. ε-Poly-l-lysine (ε-PL) is a novel preservative with strong inhibitory effects on fungi, and has the capacity to induce disease resistance in fruit, but the mechanism has been reported rarely, especially in citrus. In the present study, 800 μg/mL ε-PL and P. digitatum spores were inoculated in two different wounds on the citrus pericarp at an interval of 24 h. The results revealed that ε-PL inhibited that the development of green mold without direct contact with P. digitatum, indicating that the disease resistance of citrus was activated. Transcriptome analysis revealed that ε-PL activated amino acid metabolism and phenylpropanoid biosynthesis. Besides, the accumulation of glutamic acid, proline, arginine, serine, lysine, phenylalanine, and tyrosine were changed during storage. In phenylpropanoid biosynthesis, ε-PL increased phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate:coenzyme A ligase (4CL) activities and total phenolic and flavonoid contents. Importantly, among these phenolic compounds, ε-PL promoted the accumulation of individual phenolic compounds including ferulic acid, chlorogenic acid, p-coumaric acid, caffeic acid, gallic acid, catechins, epicatechin, and narirutin. In conclusion, ε-PL enhanced the resistance of citrus through amino acid metabolism and accumulation of phenolic compounds. These results improved the knowledge of the mechanism of ε-PL–induced disease resistance and provided a fresh theoretical basis for the use of ε-PL in postharvest citrus preservation.

Comparison of Proanthocyanidin- and Phenolic-Rich Extracts Derived from Pecan Shell and Husk as Elicitors of Induced Resistance Against Phytophthora capsici on Chile Pepper

The use of plant-derived secondary metabolites to induce disease resistance in plants has been well documented. In this study, total phenolics and total proanthocyanidins (PACs) were extracted from the shell and husk of pecan ( Carya illinoinensis) and quantified. Under greenhouse conditions, the extracts were foliarly applied to chile pepper ( Capsicum annuum, cultivar NM 6-4) to compare their ability to induce resistance in plants inoculated with a virulent isolate of Phytophthora capsici. Extractions yielded total phenolic contents of 673 ± 28 and 293 ± 24 mg/g dry weight (DW) for shell and husk and total PAC contents of 1,770.10 ± 158.62 and 901.30 ± 22.84 mg/g DW for shell and husk, respectively. Chile plants treated with total phenolic and PAC extracts from pecan husk or shell or 0.1% salicylic acid, a plant-defense hormone, remained asymptomatic throughout the study for 3 weeks, whereas plants treated with water, which served as a control, died. Both total phenolic and total PAC extracts derived from pecan byproducts can be used within a greenhouse setting as elicitors to induce resistance response in chile pepper against plant pathogens such as P. capsici.

Macroalgal treatment to alleviate the strawberry yield loss caused by Macrophomina phaseolina (Tassi) Goid. in greenhouse cultivation system

The application of algae has been considered a key element for integrated disease management in sustainable agriculture. These organisms can act as a bio-stimulant for induction of resistance against a variety of abiotic and biotic agents that cause economical loss to crop production globally. Charcoal rot disease caused byMacrophomina phaseolina(Tassi) Goid. is one of the biotic agents restricting strawberry (Fragaria×ananassaDuch.) yield in many cultivation sites. Herein, the foliar application of brown alga (Sargassum angustifolium) was investigated for the reduction of the disease symptoms and improvement of vegetative and reproductive indices in strawberries under greenhouse conditions. The results showed that alga-treated infected plants showed symptom remission. Moreover, vegetative and reproductive indices of alga-treated plants were significantly improved. Biochemical analysis showed that in alga-treated infected plants the total phenol, flavonoids, and total antioxidant activity were significantly increased compared to non-treated infected plants. Furthermore, the content of defense-related enzymes, viz. phenylalanine ammonia-lyase and polyphenol oxidase, were significantly increased in the infected plants pre-treated with the alga extract. Foliar application ofS. angustifoliumextract can induce defense responses in strawberry plants infected byM. phaseolinaleading to improved growth indices of the plants. It can be concluded thatS. angustifoliumextract is a promising source of bio-stimulants for induction of disease resistance against charcoal rot disease in strawberry cultivations.

Hydropriming and Osmotic Priming Induce Resistance against Aspergillus niger in Wheat (Triticum aestivum L.) by Activating β-1, 3-glucanase, Chitinase, and Thaumatin-like Protein Genes.

Priming is used as a method to improve plant growth and alleviate the detrimental effects of pathogens. The present study was conducted to evaluate the effects of different priming methods in the context of resistance to Aspergillus niger in wheat (Triticum aestivum L.). Here, we show that different priming treatments-viz., hydropriming, osmotic priming, halopriming, and hormonal priming techniques can induce disease resistance by improving the biochemical contents of wheat, including chlorophyll, protein, proline, and sugar. In addition, physiological parameters-such as root length, shoot length, fresh and dry root/shoot ratios, and relative water content were positively affected by these priming methods. In essence, hydropriming and osmotic priming treatments were found to be more potent for enhancing wheat biochemical contents, along with all the physiological parameters, and for reducing disease severity. Hydropriming and osmotic priming significantly decreased disease severity, by 70.59-75.00% and 64.71-88.33%, respectively. RT-PCR and quantitative real-time PCR analyses of potentially important pathogenesis-related (PR)-protein genes (Thaumatin-like protein (TLP), chitinase, and β-1,3-glucanase) in primed plants were evaluated: β-1,3-glucanase was most highly expressed in all primed plants; Chitinase and TLP exhibited higher expression in hormonal-, halo-, osmotic-, and hydro-primed plants, respectively. These results suggest that the higher expression of β-1,3-glucanase, TLP, and chitinase after hydropriming and osmotic priming may increase disease resistance in wheat. Our study demonstrates the greater potential of hydropriming and osmotic priming for alleviating stress caused by A. niger inoculation, and enhancing resistance to it, in addition to significantly improving plant growth. Thus, these priming methods could be beneficial for better plant growth and disease resistance in other plants.

Defense Surveillance System at the Interface: Response of Rice Towards Rhizoctonia solani During Sheath Blight Infection.

Sheath blight of rice caused by necrotrophic plant pathogen Rhizoctonia solani is one of the most common fungal diseases of rice leading to significant yield loss. Among the defense responses exhibited by the host plants towards fungal infections, those functional within the apoplast contribute significantly. Here, we have studied apoplastic defense response of rice towards R. solani during sheath blight infection. The transcriptome of R. solani-infected rice plants was compared with that of uninfected rice, to identify the set of defense genes that undergo differential expression and code for proteins with a predicted N-terminal signal peptide. Significant changes in the stress-responsive, molecular signal perception, protein modification, and metabolic process pathways represented by a group of differentially expressed genes were observed. Our data also revealed two secreted protease inhibitors from rice that exhibit increased expression during R. solani infection and induce disease resistance when expressed in Nicotiana benthamiana. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Chitin-induced systemic disease resistance in rice requires both OsCERK1 and OsCEBiP and is mediated via perturbation of cell-wall biogenesis in leaves.

Chitin is a well-known elicitor of disease resistance and its recognition by plants is crucial to perceive fungal infections. Chitin can induce both a local immune response and a systemic disease resistance when provided as a supplement in soils. Unlike local immune responses, it is poorly explored how chitin-induced systemic disease resistance is developed. In this study, we report the systemic induction of disease resistance against the fungal pathogen Bipolaris oryzae by chitin supplementation of soils in rice. The transcriptome analysis uncovered genes related to cell-wall biogenesis, cytokinin signaling, regulation of phosphorylation, and defence priming in the development of chitin-induced systemic response. Alterations of cell-wall composition were observed in leaves of rice plants grown in chitin-supplemented soils, and the disease resistance against B. oryzae was increased in rice leaves treated with a cellulose biosynthesis inhibitor. The disruption of genes for lysin motif (LysM)-containing chitin receptors, OsCERK1 (Chitin elicitor receptor kinase 1) and OsCEBiP (Chitin elicitor-binding protein), compromised chitin-induced systemic disease resistance against B. oryzae and differential expression of chitin-induced genes found in wild-type rice plants. These findings suggest that chitin-induced systemic disease resistance in rice is caused by a perturbation of cell-wall biogenesis in leaves through long-distance signalling after local recognition of chitins by OsCERK1 and OsCEBiP.

Control Efficacy of Salicylic Acid Microcapsules against Postharvest Blue Mold in Apple Fruit.

Salicylic acid (SA) is a natural inducer of disease resistance in fruit, but its application in the food industry is limited due to low water solubility. Here, SA was encapsulated in β-cyclodextrin (β-CD) via the host-guest inclusion complexation method, and the efficacy of SA microcapsules (SAM) against blue mold caused by Penicillium expansum in postharvest apple fruit was elucidated. It was observed that SAM was the most effective in inhibiting the mycelial growth of P. expansum in vitro. SAM was also superior to SA for control of blue mold under in vivo conditions. Enzyme activity analysis revealed that both SA and SAM enhanced the activities of superoxide dismutase (SOD) and phenylalanine ammonia lyase (PAL) in apple fruit, whereas SAM led to higher SOD activities than SA. Total phenolic contents in the SAM group were higher than those in the SA group at the early stage of storage. SAM also improved fruit quality by retarding firmness loss and maintaining higher total soluble solids (TSS) contents. These findings indicate that microcapsules can serve as a promising formulation to load SA for increasing P. expansum inhibition activity and improving quality attributes in apple fruit.

Antimicrobial peptide CB-M exhibits direct antifungal activity against Botrytis cinerea and induces disease resistance to gray mold in cherry tomato fruit

Gray mold is a common postharvest disease caused by Botrytis cinerea that causes fruit decay and reduces fruit storage quality. In this study, the antifungal activity of antimicrobial peptide CB-M against B. cinerea and its mechanism of action, as well as the ability of CB-M to induce disease resistance in cherry tomato fruit, were investigated. CB-M had a strong inhibitory effect on spore survival and mycelial growth of B. cinerea, and these effects were enhanced with increased CB-M concentration. Moreover, significant leakages of cellular constituents and fluorescence microscopy assay confirmed that CB-M treatment could destroy the cell membrane integrity of B. cinerea. Scanning electron microscopy observations further demonstrated obvious distortion and shriveling of B. cinerea hyphae. Gel retardation and SDS-PAGE assay showed that CB-M could likely bind to cellular DNA and degrade/inhibit protein synthesis in B. cinerea. Furthermore, preincubation with CB-M before pathogen inoculation significantly decreased lesion diameter and incidence of gray mold caused by B. cinerea in tomato, cherry tomato, and grape fruit throughout whole storage time. Cherry tomato was used to explore the ability of CB-M to induce gray mold resistance, and the results showed that CB-M preincubation enhanced the activities of superoxide dismutase, peroxidase, and catalase, accelerated the accumulation of pathogenesis-related proteins, flavonoids, and total phenolics, and increased the activities of β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase during storage. These results indicated that CB-M is a good substitute for fungicides and has excellent prospects for controlling postharvest gray mold in horticultural crops.

Antifungal activity of natamycin against kiwifruit soft rot caused by Botryosphaeria dothidea and potential mechanisms

Soft rot caused by Botryosphaeria dothidea leads to massive economic losses in the kiwifruit industry. Natamycin is a natural antimicrobial preservative that effectively prevents postharvest decay and preserves fruit quality. However, the ability to control kiwifruit soft rot and potential antifungal mechanisms have not been explored. In this study, the inhibitory impact of natamycin against soft rot caused by B. dothidea, as well as its putative action mechanisms were investigated. The results indicated that 2 mg L−1 natamycin effectively inhibited mycelial growth and spore germination of B. dothidea in vitro. Natamycin caused B. dothidea hypha to shrink and deform, along with vacuolation and plasmolysis in hypha cells, as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Likewise, natamycin stimulated the accumulation of reactive oxygen species (ROS) in the hypha. The inhibition effect of natamycin on B. dothidea inoculated in kiwifruit was dose-dependent, with 500 mg L−1 natamycin significantly decreasing the incidence of soft rot to 35%. Furthermore, natamycin induced disease resistance in kiwifruit tissue by activating the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT), increasing the antioxidant compound total phenol, maintaining a low level of malondialdehyde (MDA), and repressing the activity of four cell wall degrading enzymes, as well as gene expression of β-galactosidase (β-Gal) and polygalacturonase (PG). Further field research revealed that pre-harvest treatment combined with the postharvest natamycin application significantly reduced the natural decay incidence of kiwifruit while having no negative effect on soft-ripe quality. In conclusion, our findings proved that natamycin has an antifungal effect on B. dothidea and may be applied as a safe preservative to reduce soft rot.

Nutrient Elements Promote Disease Resistance in Tomato by Differentially Activating Immune Pathways.

Nutrient elements play essential roles in plant growth, development, and reproduction. Balanced nutrition is critical for plant health and the ability to withstand biotic stress. Treatment with essential elements has been shown to induce disease resistance in certain cases. Understanding the functional mechanisms underlying plant immune responses to nutritional elements has the potential to provide new insights into crop improvement. In the present study, we investigated the effect of various elements-potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)-in promoting resistance against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Xanthomonas euvesicatoria in tomato. We demonstrate that spray treatment of essential elements was sufficient to activate immune responses, inducing defense gene expression, cellular leakage, reactive oxygen species, and ethylene production. We report that different defense signaling pathways are required for induction of immunity in response to different elements. Our results suggest that genetic mechanisms that are modulated by nutrient elements can be exploited in agricultural practices to promote disease resistance.

Plant defense elicitor, 2, 4-dichloro-6-{(E)-[(3-methoxyphenyl) imino] methyl} phenol (DPMP) and its mode of action against fungal pathogen Alternaria solani in tomato (Solanum lycopersicum L.)

Biotic stress factors are one of the major constraints plants face, and they significantly affect production and yield. There are multiple ways to cope with stress factors, including genetic enhancement. When they cannot provide sufficient protection, pesticides are commonly applied. Plant defense elicitors are a new approach for boosting plants' natural immune responses and tolerance levels. The newly identified promising plant defense elicitor; 2, 4-dichloro-6-{(E)-[(3-methoxyphenyl) imino] methyl} phenol (DPMP) was previously studied against the oomycete Hyaloperonospora arabidopsidis, the bacterial pathogens Pseudomonas syringae and Clavibacter michiganensis ssp michiganensis and found to induce disease resistance against these phytopathogens. However, it was not tested against fungal pathogens. Here for the first time, DPMP was evaluated against one of the most destructive fungal pathogens, Alternaria solani. Disease severity and plant development were evaluated. The results revealed that DPMP neither inhibited nor enhanced the disease severity of A. solani. Gene expression of several salicylic acid, jasmonic acid, and ethylene pathway-related genes (Pti4, TPK1b, Pto kinase, PRB1‐2, SABP2, and PR3) were also analyzed. According to the results, while DPMP induces PRB1-2, TPK1b, and Pto kinase gene expressions, the protection against A. solani does not occur via these genes. PR3 is one of the most important genes for defense responses against necrotrophic pathogens, and DPMP downregulated gene expression of PR3. These results demonstrated that DPMP mostly takes a role through the SA-related defense pathway and was effective against biotrophic and hemibiotrophic pathogens. However, it is not suitable for protection against the necrotrophic pathogen A. solani. Further research may pinpoint the activity of DPMP on the defense pathway and provide a better understanding of the mode of action for DPMP and other plant elicitors for specific plant protection solutions.

Kojic acid induces resistance against Colletotrichum brevisporum and enhances antioxidant properties of postharvest papaya

Once harvested, papaya fruit is prone to rapid deterioration and spoilage by microorganisms leading to food loss. The current study aimed to evaluate the effect of kojic acid (KA) treatments (2 mM and 5 mM) on the resistance of postharvest papaya against Colletotrichum brevisporum, a hazardous fungal pathogen. The results indicated that KA treatment decreased the lesion length in papayas by 30% after 7 days of storage. In addition, KA promoted the activity of both superoxide dismutase (SOD) and catalase (CAT) enzymes. Consequently, a decrease in malondialdehyde (MDA), hydrogen peroxide (H2O2) and nitric oxide (NO) contents was also observed. Furthermore, the application of KA enhanced the antioxidant activity and expression levels of several genes related to antioxidant properties and defense response in papaya. In this regard, the effects of KA on C. brevisporum-infected postharvest papaya were studied for the first time, revealing the ability of KA to induce disease resistance and enhance the antioxidant properties in postharvest papaya.

Disease resistance induction by K. marxianus against green mold in citrus via transcriptome analysis and verification based on metabolites

This study examined the transcriptional composition and changes in gene expression patterns in citrus fruit tissue treated with Kluyveromyces marxianus and its effects on key defense-related enzyme activities and metabolites. This analysis was carried out by the technique of RNA sequencing, the use of HPLC-MS, and GC–MS equipment. The sequencing data revealed that the induction of K. marxianus in the citrus fruit peel activated the expression of genes in 90 biological pathways. A total of 3785 genes were transcribed between the yeast-treated and control fruits. 1287 genes were expressed significantly, 682 genes were up-regulated representing 52.99 %, and 605 genes were down-regulated representing 47.00 %. Gene expressions in some of the pathways in the treated citrus stimulated an increase in the production of some defense-related enzymes, the synthesis of secondary metabolites such as phenolic compounds, flavonoids, phenolic acids, and an enhanced lignin production. The accumulation of these compounds contributed to the improvement of the antifungal activity and defense responses in the citrus. 8 phenolic acids, 12 sugars, 6 organic acids, and 17 amino acids were detected at varying concentrations. The investigations revealed that the production of the metabolites was significantly enhanced in the K. marxianus-treated fruits as compared to the control fruits. The study provides some fundamental understanding of the induced resistance mechanism in citrus by K. marxianus.

PpMYB308 is involved in Pichia guilliermondii-induced disease resistance against Rhizopus rot by activating the phenylpropanoid pathway in peach fruit

Pichia guilliermondii has been shown to control fungal decay in various harvested fruits by inducing disease resistance, but the transcriptional regulatory mechanism remains unclear. In our study, P. guilliermondii treatment induced resistance against soft rot caused by Rhizopus stolonifer in peach fruit, as shown by the reduced disease incidence and severity, increased enzyme activities and gene expression of phenylalanine ammonia-lyase (PAL) and 4-coumarate-CoA ligase (4CL), and promoted the accumulation of total phenolics, total flavonoids and the main individual phenolic compounds (neochlorogenic acid, chlorogenic acid, gallic acid, and rutin). In addition, P. guilliermondii induced the expression of PpMYB308, which was identified as a nucleus‐localized transcriptional activator of PpPAL1 and Pp4CL5 by binding to the MREs (MYB recognition elements). Moreover, the transient overexpression of PpMYB308 in peach fruit enhanced the expression of PpPAL1 and Pp4CL5 and reduced disease incidence and severity. Therefore, the results indicate that PpMYB308 is involved in P. guilliermondii-induced disease resistance against R. stolonifer by activating the phenylpropanoid pathway.

Insights into the defense mechanisms involved in the induction of resistance against black spot of cherry tomatoes by Pichia caribbica

Our previous study showed that Pichia caribbica could alleviate black spot of cherry tomatoes. This study aimed to explore the comprehensive mechanisms involved in the induced disease resistance of cherry tomatoes by this yeast. The results indicated that P. caribbica increased the activities of defense-related enzymes and enzymes of phenylpropanoid pathway including polyphenol oxidase, chitinase, β-1,3-glucanase, phenylalanine ammonia-lyase and cinnamate-4-hydroxylase in the fruits. Considering together with transcriptome analysis results, it was suggested that P. caribbica triggered mitogen-activated protein kinase, Ca2+ and plant hormone signaling pathways, up-regulated genes related to reactive oxygen species scavenging, induced defense-related genes and enzyme activities, and stimulated genes and the activities of enzymes involved in secondary metabolite synthesis to accumulate total phenols, lignin and flavonoids, thus enhancing the resistance of cherry tomatoes against black spot. This study will provide new insights into the underlying mechanisms involved in induced disease resistance of cherry tomatoes by antagonistic yeast.

Exogenous Melatonin Treatment Induces Disease Resistance against Botrytis cinerea on Post-Harvest Grapes by Activating Defence Responses.

Botrytis cinerea seriously affects the value of post-harvest grapes. Melatonin can act as an exogenous regulator in the resistance of exogenous pathogens due to its antioxidant activity. An artificial inoculation trial was conducted to research the induced resistance mechanism of melatonin treatment using the table grape “Muscat Hamburg” (Vitis vinifera L. cv). Grapes were immersed with 0.02, 0.2, and 2 mmol/L melatonin, followed by B. cinerea suspension injections after 48 h. The results showed that the mycelial growth and spore germination of B. cinerea was not significantly inhibited by melatonin at different concentrations (0.02–2 mmol/L). However, post-harvest melatonin treatment inhibited the increase of disease incidence and severity of grey mould, induced the synthesis and accumulation of total phenols and flavonoids, reduced malondialdehyde generation, and inhibited an increase in cell membrane permeability. Meanwhile, defensive enzyme activities, including superoxide dismutase (SOD), peroxidize (POD), catalase (CAT), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), chitinase (CHI), and β-1,3-glucanase, were significantly increased in fruits treated with exogenous melatonin. These results suggested that exogenous melatonin treatment could activate defence responses to combat the infection of B. cinerea in post-harvest grapes.

Efficacy of Meyerozyma caribbica in the biocontrol of blue mold in kiwifruit and mechanisms involved

Kiwifruit are susceptible to Penicillium expansum infestation, resulting in decay and causing severe economic losses. In this study, we investigated the efficacy and related mechanism of Meyerozyma caribbica in controlling and preventing of P. expansum. The yeast was found to significantly reduce the disease incidence of blue mold in kiwifruit, inhibit the growth of P. expansum in vitro, and reduce both the spore germination rate and germ tube length in a dose-dependent manner. Meanwhile, M. caribbica can stably growth on kiwifruit at 20℃ and 4℃ and had the ability to form biofilm. In addition, the results of this study also showed that M. caribbica induced an increase in polyphenol oxidase (PPO), peroxidase (POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), and phenylalanine ammonia lyase (PAL) activities of kiwifruit and reduced the content of malondialdehyde (MDA). The content of secondary metabolites such as total phenols, flavonoids, and lignin were also increased after yeast application. These experiments indicate that M. caribbica has a strong adaptation to the environment and relies on competition for nutrients and space against pathogens. The induction of disease resistance in fruits is also one of the important mechanisms to control the occurrence of blue mold in kiwifruit. In summary, M. caribbica has the potential to be an antagonistic yeast for controlling postharvest blue mold of kiwifruit.

Postharvest biological control of Botrytis cinerea and the mechanisms underlying the induction of disease resistance in grapes by Lactobacillus plantarum CM-3

Biological control by microbial antagonists has been proposed as a viable strategy for the control of postharvest diseases in fruit. In the present study, biocontrol efficacy of the bacterial antagonist Lactobacillus plantarum CM-3 against gray mold infection on harvested grapes was documented along with the underlying physiological and molecular mechanisms responsible for biocontrol activity. In this regard, a transcriptomic analysis of the response of grapes to L. plantarum CM3 was conducted. Results indicated that L. plantarum CM-3 significantly decreased the level of natural postharvest decay in grapes without causing any adverse effects on quality traits. Treatment of grapes with L. plantarum CM-3 (1 × 109 CFU mL−1) resulted in a 55 % reduction in disease incidence caused by Botrytis cinerea. Meanwhile, L. plantarum CM-3 enhanced the activity of several enzymes in grapes that are closely associated with defense, including POD, PPO, CAT, APX, PAL, and GLU. RNA-seq analysis indicated extensive changes in the gene expression profile of grape berries in response to being treated with L. plantarum CM-3. In total, 1,327 differentially expressed genes (DEGs) were identified, among which 78.1 % (1,037) were upregulated and 21.9 % (290) were downregulated. Numerous pathways were strongly influenced by the L. plantarum CM-3 treatment, including signal perception and transduction, maintenance of reactive oxygen species (ROS) homeostasis, transcriptional and post-transcriptional regulation, primary metabolic pathways, and secondary metabolism. Additionally, the expression of 22 DEGs linked to enhancing disease resistance was analyzed by RT-qPCR and their expression levels were found to well correspond with the results obtained in the analysis of the RNA-seq data. Our data indicate that L. plantarum CM-3 can enhance host resistance by altering the expression of defense genes and their corresponding proteins, including PR1, WRKY33, WRKY22, PTI6 and peroxidase isoenzyme. Collectively, results of our study indicate that L. plantarum CM-3 treatment enhances the disease resistance of harvested grapes through a comprehensive and complex regulatory network. These findings provide new information on the molecular mechanism responsible for the enhancement of host disease resistance in grapes by L. plantarum CM-3. It also demonstrates a biocontrol strategy that can be used to elicit defense responses in fruit against fungal pathogens.

Melatonin induces improved protection against Botrytis cinerea in cherry tomato fruit by activating salicylic acid signaling pathway

Melatonin modulated immune responses to various stresses in plants. However, the crosstalk between melatonin and the other signal molecules, especially with salicylic acid (SA), is largely unclear in fruit. The objective of this research was to investigate the mechanism of melatonin induced disease resistance in cherry tomato fruit. The results indicated that melatonin treatment significantly inhibited gray mold development, induced reactive oxygen species (ROS) burst, enhanced SA accumulation accompanied by increasing its synthesis-related enzymes activity, up-regulated expression of defense genes, including SlWRKY70, SlNPR1, SlTGA5, SlPR1, SlPR2 and SlGLU, but decreased nitric oxide (NO) content during storage. Moreover, melatonin treatment increased endogenous melatonin content by up-regulating the expressions of SlTDC, SlSNAT and SlASMT in fruit during storage. However, the melatonin-enhanced disease resistance in fruit was completely abolished by a paclobutrazol (PAC) (SA biosynthesis inhibitor) treatment. Thus, the results suggested that hydrogen peroxide (H2O2) and SA signaling pathway would be collectively involved in melatonin induced-disease resistance in cherry tomato fruit during storage.

Exogenous genistein enhances soybean resistance to Xanthomonas axonopodis pv. glycines.

Xanthomonas axonopodis pv. glycines (Xag) is the causal agent of bacterial pustule disease and results in enormous losses in soybean production. Although isoflavones are known to be involved in soybean resistance against pathogen infection, the effects of exogenous isoflavones on soybean plants remain unexplored. Irrigation of soybean plants with isoflavone genistein inhibited plant growth for short periods, probably by inhibiting the tyrosine (brassinosteroids) kinase pathway, and increased disease resistance against Xag. The number of lesions was reduced by 59%-63% when applying 50 μg ml-1 genistein. The effects on disease resistance were observed for 15 days after treatment. Genistein also enhanced the disease resistance of soybean against the fungal pathogen Sclerotinia sclerotiorum. Exogenous genistein increased antioxidant capacity, decreased H2 O2 level and promoted the accumulation of phenolics in Xag-infected soybean leaves. Exogenous genistein reduced the amounts of endogenous daidzein, genistein and glycitein and increased the concentration of genistin, which was found to show strong antibacterial activity against the pathogen and to reduce the expression of virulence factor yapH, and flagella formation gene flgK. The expression of several soybean defense genes, such as chalcone isomerase, glutathione S-transferase and 1-aminocyclopropane-1-carboxylate oxidase 1, was upregulated after genistein treatment. The effects of exogenous genistein on soybean plants were examined for the first time, revealing new insights into the roles of isoflavones in soybean defense and demonstrating that irrigation with genistein can be a suitable method to induce disease resistance in soybean plants. © 2022 Society of Chemical Industry.