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The molecular mechanisms of plant responses to phytophagous insect eggs are poorly understood, despite their importance in insect–plant interactions. This study investigates the plant defense mechanisms triggered by the eggs of whitefly Bemisia tabaci, a globally significant agricultural pest. A transcriptome comparison of tobacco plants with and without eggs revealed that whitefly eggs may activate the response of defense-related genes, including those involved in the salicylic acid (SA) signaling pathway. SA levels are induced by eggs, resulting in a reduction in egg hatching, which suggests that SA plays a key role in plant resistance to whitefly eggs. Employing Agrobacterium-mediated transient expression, virus-induced gene silencing assays, DNA–protein interaction studies, and bioassays, we elucidate the regulatory mechanisms involved. Pathogenesis-related proteins NtPR1-L1 and NtPR5-L2, downstream of the SA pathway, also affect whitefly egg hatching. The SA-regulated transcription factor NtWRKY70a directly binds to the NtPR1-L1 promoter, enhancing its expression. Moreover, NtPR1-L1 promotes callose deposition, which may impede the eggs' access to water and nutrients. This study establishes the SA-WRKY70-PR-callose axis as a key mechanism linking plant responses and defenses against whitefly eggs, providing new insights into the molecular interactions between plants and insect eggs. [ABSTRACT FROM AUTHOR]

The brown planthopper (BPH) is the most destructive insect pest in rice. Through a stylet, BPH secretes a plethora of salivary proteins into rice phloem cells as a crucial step of infestation. However, how various salivary proteins function in rice cells to promote insect infestation is poorly understood. Among them, one of the salivary proteins is predicted to be a carbonic anhydrase (Nilaparvata lugens carbonic anhydrase [NlCA]). The survival rate of the NlCA- RNA interference (RNAi) BPH insects was extremely low on rice, indicating a vital role of this salivary protein in BPH infestation. We generated NlCA transgenic rice plants and found that NlCA expressed in rice plants could restore the ability of NlCA- RNAi BPH to survive on rice. Next, we produced rice plants expressing the ratiometric pH sensor pHusion and found that NlCA- RNAi BPH induced rapid intracellular acidification of rice cells during feeding. Further analysis revealed that both NlCA- RNAi BPH feeding and artificial lowering of intracellular pH activated plant defense responses and that NlCA-mediated intracellular pH stabilization is linked to diminished defense responses, including reduced callose deposition at the phloem sieve plates and suppressed defense gene expression. Given the importance of pH homeostasis across the kingdoms of life, discovery of NlCA-mediated intracellular pH modulation uncovered a new dimension in the interaction between plants and piercing/sucking insect pests. The crucial role of NlCA for BPH infestation of rice suggests that NlCA is a promising target for chemical or trans-kingdom RNAi-based inactivation for BPH control strategies in plants. • Rapid intracellular acidification is a novel plant defense response • Brown planthopper (BPH) delivers carbonic anhydrase (NlCA) into rice for survival • NlCA counters intracellular acidification to suppress plant defense • pH-responsive regulators of defense responses are predicted to exist in the rice-BPH interaction The brown planthopper (BPH) is the most devastating insect pest in rice. Jiang et al. discover that BPH secretes a salivary carbonic anhydrase (NICA) to regulate the intracellular pH of the rice cell to facilitate its feeding and survival on rice plants and that NICA counters host intracellular pH acidification to diminished defense responses. [ABSTRACT FROM AUTHOR]

Fusarium graminearum, a devastating fungal pathogen, causes great economic losses to crop yields worldwide. The present study investigated the potential of Streptomyces pratensis S10 to alleviate F. graminearum stress in wheat seedlings based on plant growth-promoting and resistance-inducing assays. The bioassays revealed that S10 exhibited multiple plant growth-promoting properties, including the production of siderophores, 1-aminocyclopropane-1-carboxylic acid deaminase (ACC), and indole-3-acetic acid (IAA), phosphate solubilization, and nitrogen fixation. Meanwhile, the pot experiment demonstrated that S10 improved wheat plant development, substantially enhancing wheat height, weight, root activity, and chlorophyll content. Consistently, genome mining identified abundant genes associated with plant growth promotion. S10 induced resistance against F. graminearum in wheat seedlings. The disease incidence and disease index reduced by nearly 52% and 65% in S10 pretreated wheat seedlings, respectively, compared with those infected with F. graminearum only in the non-contact inoculation assay. Moreover, S10 enhanced callose deposition and reactive oxygen species (ROS) accumulation and induced the activities of CAT, SOD, POD, PAL, and PPO. Furthermore, the quantitative real-time PCR (qRT-PCR) results indicated that S10 pretreatment increased the expression of SA- (PR1.1, PR2, PR5, and PAL1) and JA/ET-related genes (PR3, PR4a, PR9, and PDF1.2) in wheat seedlings upon F. graminearum infection. In summary, S. pratensis S10 could be an integrated biological agent and biofertilizer in wheat seedling blight management and plant productivity enhancement. [ABSTRACT FROM AUTHOR]

Abstract Background Soybean mosaic disease caused by soybean mosaic virus (SMV) is one of the most devastating and widespread diseases in soybean producing areas worldwide. The WRKY transcription factors (TFs) are widely involved in plant development and stress responses. However, the roles of the GmWRKY TFs in resistance to SMV are largely unclear. Results Here, 185 GmWRKYs were characterized in soybean (Glycine max), among which 60 GmWRKY genes were differentially expressed during SMV infection according to the transcriptome data. The transcriptome data and RT-qPCR results showed that the expression of GmWRKY164 decreased after imidazole treatment and had higher expression levels in the incompatible combination between soybean cultivar variety Jidou 7 and SMV strain N3. Remarkably, the silencing of GmWRKY164 reduced callose deposition and enhanced virus spread during SMV infection. In addition, the transcript levels of the GmGSL7c were dramatically lower upon the silencing of GmWRKY164. Furthermore, EMSA and ChIP-qPCR revealed that GmWRKY164 can directly bind to the promoter of GmGSL7c, which contains the W-box element. Conclusion Our findings suggest that GmWRKY164 plays a positive role in resistance to SMV infection by regulating the expression of GmGSL7c, resulting in the deposition of callose and the inhibition of viral movement, which provides guidance for future studies in understanding virus-resistance mechanisms in soybean.

Background: Soybean mosaic disease caused by soybean mosaic virus (SMV) is one of the most devastating and widespread diseases in soybean producing areas worldwide. The WRKY transcription factors (TFs) are widely involved in plant development and stress responses. However, the roles of the GmWRKY TFs in resistance to SMV are largely unclear. Results: Here, 185 GmWRKYs were characterized in soybean (Glycine max), among which 60 GmWRKY genes were differentially expressed during SMV infection according to the transcriptome data. The transcriptome data and RT-qPCR results showed that the expression of GmWRKY164 decreased after imidazole treatment and had higher expression levels in the incompatible combination between soybean cultivar variety Jidou 7 and SMV strain N3. Remarkably, the silencing of GmWRKY164 reduced callose deposition and enhanced virus spread during SMV infection. In addition, the transcript levels of the GmGSL7c were dramatically lower upon the silencing of GmWRKY164. Furthermore, EMSA and ChIP-qPCR revealed that GmWRKY164 can directly bind to the promoter of GmGSL7c, which contains the W-box element. Conclusion: Our findings suggest that GmWRKY164 plays a positive role in resistance to SMV infection by regulating the expression of GmGSL7c, resulting in the deposition of callose and the inhibition of viral movement, which provides guidance for future studies in understanding virus-resistance mechanisms in soybean. [ABSTRACT FROM AUTHOR]

Although Nesidiocoris tenuis is highly effective as a biological control agent, it can also damage tomato plants due to its zoophytophagous behavior. When N. tenuis pierces the stems and petioles of tomato plants with its stylets, it triggers callose deposition and subsequent cell death, resulting in blocked nutrient transport, floral abortions, or wilting of tender shoots. Recently, it has been shown that exposure of tomato plants to the green leaf volatile (Z)-3-hexenyl propanoate [(Z)-3-HP] activates defensive mechanisms, including the regulation of genes involved in the synthesis and degradation of callose. In this study, conducted under greenhouse conditions, we tested the hypothesis that damage caused by N. tenuis could be reduced by exposing tomato plants to (Z)-3-HP through polymeric dispensers. Tomato plants exposed to (Z)-3-HP and non-exposed control plants were inoculated with N. tenuis. Nesidiocoris tenuis established in both groups with no significant differences between the two treatments. However, as hypothesized, the damage caused by N. tenuis was significantly lower in the plants exposed to (Z)-3-HP. Gene expression analysis of salicylic, jasmonic, and abscisic acids, along with histochemical staining methods, was used to compare the defensive responses of tomato plants infested solely with N. tenuis versus those infested with N. tenuis and exposed to (Z)-3-HP. Our findings confirm the influence of (Z)-3-HP exposure on differential defensive activation between treatments and reduced callose deposition in (Z)-3-HP-exposed plants. These results pave the way for improved management of N. tenuis by enhancing the plant's defenses based on inter-plant communication.

Infection of tomato leaves and fruits by necrotrophic fungal pathogen Botrytis cinerea causes considerable economic loss. Melatonin has multiple physiological functions and is considered a potential biocontrol agent for its positive effects on plant innate immunity. In tomato, melatonin reduces Botrytis-caused post-harvest fruit decay by activating jasmonic acid (JA) signaling. In this study, we analyzed the effects of melatonin on resistance to Botrytis and associated defense mechanisms in tomato leaves. Treatment of detached tomato leaves with melatonin at a concentration as low as 100 µM induced resistance to Botrytis based on reduced lesion size and fungal growth. Melatonin-induced resistance to gray mold was associated with activation of a complex set of defense mechanisms in tomato leaves. First, melatonin suppressed Botrytis-induced cell death and accumulation of reactive oxygen species (ROS), which was correlated with increased activities of ROS-scavenging enzymes and enhanced expression of their corresponding genes. Second, melatonin treatment induced callose synthase genes and promoted rapid and strong callose deposition in tomato leaves. Melatonin also induced other anti-microbial genes encoding chitinases, β-1,3-glucanases, phenylalanine ammonialyases and polyphenol oxidases. Third, melatonin increased Botrytis-induced expression of genes encoding SlWRKY33, SlMYC2 and SlERF transcription factors, which activate defense-related genes expression through JA and ethylene (ET) signaling pathways. By contrast, melatonin suppressed salicylic acid (SA) signaling based on reduced expression of the SlPR1 marker gene, which is known to antagonize defense against Botrytis. These results collectively indicate that exogenous melatonin orchestrates multiple signaling pathways to activate a complex set of defense mechanisms against Botrytis in tomato leaves.

Despite significant nutritional value and vast expanse under chickpea cultivation, fungi‐borne diseases are the main limiting factors to increasing its yield. Botrytis grey mould (BGM) is a major foliar disease knocking chickpeas sideways. Thus, to compensate for economic yield loss, BGM‐resistant lines must be fished through an effective screening technique. In the present study, carbohydrates, mainly callose, were observed as vital actors in conferring varietal resistance. The study was done on disease reaction of BGM through microscopy for callose quantification in nine varieties and a susceptible check. The detection of noticeable callose deposits induced in leaf samples collected from artificially inoculated BGM sick plots was studied under a fluorescent microscope. Quantification of callose deposition was done using 1–5 rating scale where grades show intensity of callose accumulated. It was first report in chickpea to uncover the presence of callose in cellular regions by observing the blue fluorescence produced by aniline dye. Further characterization revealed varietal differences for callose deposits. Variations in endogenous sugar contents in the leaves during infection revealed the presence of complex dynamics of callose as a function of defence and resistance against infection. Based on this, PG 186, PG 5 and PG 6 showed significant amount of callose against the cell wall while H 208 scored minimum, thus in agreement with the use of this variety as a susceptible check. [ABSTRACT FROM AUTHOR]

Durian (Durio zibethinus L.) is susceptible to Phytophthora palmivora, which causes rot disease, leading to significant yield loss. This study aimed to investigate local defense responses of durian to P. palmivora and compare the infection dynamics of high virulence (HV) and low virulence (LV) isolates. Durian leaves on 1-year-old seedlings were inoculated with mycelial plugs. Symptoms were observed within 24 h. The HV-isolate was more aggressive, leading to larger lesions, earlier and denser colonization, and higher sporulation. P. palmivora lifestyle related gene (PpEF1α, PpHmp1, PpCdc14, and PpOPEL) were expressed at a higher level in HV compared to LV. Local defense response showed intense accumulation of H2O2, with a stronger response to the HV. Callose deposition increased initially but declined after inoculation, with different diameters between isolates, but no significantly different intensity patterns. These findings provide insights into the P. palmivora-durian interaction, with potential applications in improving disease management strategies. [ABSTRACT FROM AUTHOR]

In agroecosystems, plants frequently confront multiple biotic stressors, including herbivores and pathogens. The nature of these interactions plays a crucial role in mediating the activation of plant defense mechanisms. However, induction of plant chemical defenses has been more well studied than the induction of physical defenses. Here, we assessed the physical and chemical defense responses of pea (Pisum sativum) plants after exposure to three stressors: a vector herbivore (pea aphid, Acrythosiphon pisum), a non-vector herbivore (pea leaf weevil, Sitona lineatus), and a virus (Pea enation mosaic virus, PEMV). We used various histochemical staining techniques show that viruliferous A. pisum (transmitting PEMV) strongly induced callose deposition (aniline blue staining) and antioxidant-mediated defenses (DAB and NBT staining) in peas, primarily through accumulating reactive oxygen species (ROS). High-throughput phenotyping showed that viruliferous aphids reduced plant photosynthetic efficiency, but plants infected with PEMV had increased cell death (trypan blue staining). However, herbivory by aphids and weevils did not strongly induce defenses in peas, even though weevil feeding significantly reduced pea leaf area. These results show that not all herbivores induce strong defensive responses, and plant responses to vector species depends on their virus infection status. More broadly, our results indicate that variable stressors differentially regulate various plant responses through intricate chemical and physical defense pathways. [ABSTRACT FROM AUTHOR]

BACKGROUND:Food contamination with Salmonella enterica and enterohemorrhagic Escherichia coli is among the leading causes of foodborne illnesses worldwide and crop plants are associated with > 50% of the disease outbreaks. However, the mechanisms underlying the interaction of these human pathogens with plants remain elusive. In this study, we have explored plant resistance mechanisms against these enterobacteria and the plant pathogen Pseudomonas syringae pv. tomato (Pst) DC3118, as an opportunity to improve food safety. RESULTS:We found that S. enterica serovar Typhimurium (STm) transcriptionally modulates stress responses in Arabidopsis leaves, including induction of two hallmark processes of plant defense: ROS burst and cell wall modifications. Analyses of plants with a mutation in the potentially STm-induced gene EXO70H4 revealed that its encoded protein is required for stomatal defense against STm and E. coli O157:H7, but not against Pst DC3118. In the apoplast however, EXO70H4 is required for defense against STm and Pst DC3118, but not against E. coli O157:H7. Moreover, EXO70H4 is required for callose deposition, but had no function in ROS burst, triggered by all three bacteria. The salicylic acid (SA) signaling and biosynthesis proteins NPR1 and ICS1, respectively, were involved in stomatal and apoplastic defense, as well as callose deposition, against human and plant pathogens. CONCLUSIONS:The results show that EXO70H4 is involved in stomatal and apoplastic defenses in Arabidopsis and suggest that EXO70H4-mediated defense play a distinct role in guard cells and leaf mesophyll cells in a bacteria-dependent manner. Nonetheless, EXO70H4 contributes to callose deposition in response to both human and plant pathogens. NPR1 and ICS1, two proteins involved in the SA signaling pathway, are important to inhibit leaf internalization and apoplastic persistence of enterobacteria and proliferation of phytopathogens. These findings highlight the existence of unique and shared plant genetic components to fight off diverse bacterial pathogens providing specific targets for the prevention of foodborne diseases.

Grafting is widely used to improve the stress tolerance and the fruit yield of horticultural crops. Ribonucleoprotein complexes formed by mRNAs and proteins play critical roles in the communication between scions and stocks of grafted plants. In Pyrus betulaefolia, ankyrin was identified previously to promote the long-distance movement of the ribonucleoprotein complex(PbWoxT1-PbPTB3) by facilitating callose degradation at plasmodesmata. However, the mechanism of the ankyrin-mediated callose degradation remains elusive. In this study, we discovered a β-1,3-glucanase (EC 3.2.1.39, PbPDBG) using ankyrin as a bait from plasmodesmata by co-immunoprecipitation and mass spectrometry. Ankyrin was required for the plasmodesmata-localization of PbPDBG. The grafting and bombardment experiments indicated that overexpressing PbPDBG resulted in decreased callose content at plasmodesmata, and thereby promoting the long-distance transport of the ribonucleoprotein complex. Altogether, our findings revealed that PbPDBG was the key factor in ankyrin-mediated callose degradation at plasmodesmata. [ABSTRACT FROM AUTHOR]

• The study identifies wild potato genotypes, AC1 of Solanum chacoense and AC4 of Solanum sparsipilum, and cultivar , Kufri Girdhari of Solanum tuberosum as highly resistant to late blight disease. • At field level, resistant genotypes AC4 and AC1 exhibit a novel mechanism of shedding infected leaves with a concomitant up-regulation of a systemic immune response. • The resistant genotypes exhibit robust hydrogen peroxide production, prolonged heightened SOD activity, cell death, high phenolic and flavonoid content and callose deposition at the site of infection, thus collectively arresting progression of disease. • The susceptible check Kufri Jyoti (earlier released as a resistant cultivar) has several of downstream resistant mechanisms in place, but shows a weak hypersensitive response, rendering it susceptible. • Hypersensitive response is paramount in resistance of potato species against late blight. Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most devastating disease causing colossal yield losses in potato globally. With the goal of identifying resistant potato genotypes and understanding the underlying mechanisms, nine potato genotypes comprising of wild species Solanum chacoense (AC1, AC2), Solanum sparsipilum (AC3, AC4, AC5) and Solanum spegzinii (AC6) and three potato cultivars (Kufri Jyoti [KJ], Kufri Chandramuki [KC] and Kufri Girdhari [KG]), were evaluated for their response to late blight in field, in vitro detached leaf assays and assessed by biochemical analyses. The study identified genotypes, AC1, of Solanum chacoense and AC4 of Solanum sparsipilum, and cultivar , Kufri Girdhari as highly resistant, and genotype AC6, of Solanum spegzinii as the most susceptible genotype in this study. At field level, resistant genotypes AC4 and AC1 exhibited a novel mechanism of shedding infected leaves with a concomitant up-regulation of a systemic immune response. At the cellular level, all the potato genotypes exhibited a generalized response to infection with increase in peroxidase activity and calcium- dependent protein kinase accumulation. However, the resistant genotypes exhibited robust hydrogen peroxide production, cell death and callose deposition at the site of infection, thus arresting the progression of disease. With the initial infection, AC4 and AC1 showed significant induction of peroxidase and superoxide dismutase (SOD) enzyme activities and accumulation of phenolics and flavonoids, while resistant cultivar KG, exhibited relatively high basal SOD activity. All the three resistant genotypes exhibited prolonged heightened SOD activity even towards the end of the cropping season. The study implicates hypersensitive response as paramount in resistance of potato species against late blight. The popular and susceptible cultivar Kufri Jyoti, which was introduced initially as a resistant cultivar, was found to have some of the resistance mechanisms in place, however, showed subdued hypersensitive response. [ABSTRACT FROM AUTHOR]

In agroecosystems, plants frequently confront multiple biotic stressors, including herbivores and pathogens. The nature of these interactions plays a crucial role in mediating the activation of plant defense mechanisms. However, induction of plant chemical defenses has been more well studied than the induction of physical defenses. Here, we assessed the physical and chemical defense responses of pea (Pisum sativum) plants after exposure to three stressors: a vector herbivore (pea aphid, Acrythosiphon pisum), a non-vector herbivore (pea leaf weevil, Sitona lineatus), and a virus (Pea enation mosaic virus, PEMV). We used various histochemical staining techniques show that viruliferous A. pisum (transmitting PEMV) strongly induced callose deposition (aniline blue staining) and antioxidant-mediated defenses (DAB and NBT staining) in peas, primarily through accumulating reactive oxygen species (ROS). High-throughput phenotyping showed that viruliferous aphids reduced plant photosynthetic efficiency, but plants infected with PEMV had increased cell death (trypan blue staining). However, herbivory by aphids and weevils did not strongly induce defenses in peas, even though weevil feeding significantly reduced pea leaf area. These results show that not all herbivores induce strong defensive responses, and plant responses to vector species depends on their virus infection status. More broadly, our results indicate that variable stressors differentially regulate various plant responses through intricate chemical and physical defense pathways.

The Australian finger lime (Citrus australasica) is tolerant to Huanglongbing (HLB; Citrus greening). This species can be utilized to develop HLB tolerant citrus cultivars through conventional breeding and biotechnological approaches. In this report, we conducted a comprehensive analysis of transcriptomic data following a non-choice infection assay to understand the CaLas tolerance mechanisms in the finger lime. After filtering 3,768 differentially expressed genes (DEGs), 2,396 were downregulated and 1,372 were upregulated in CaLas-infected finger lime compared to CaLas-infected HLB-susceptible 'Valencia' sweet orange. Comparative analyses revealed several DEGs belonging to cell wall, b-glucanase, proteolysis, R genes, signaling, redox state, peroxidases, glutathione-S-transferase, secondary metabolites, and pathogenesis-related (PR) proteins categories. Our results indicate that the finger lime has evolved specific redox control systems to mitigate the reactive oxygen species and modulate the plant defense response. We also identified candidate genes responsible for the production of Cys-rich secretory proteins and Pathogenesis-related 1 (PR1-like) proteins that are highly upregulated in infected finger lime relative to noninfected and infected 'Valencia' sweet orange. Additionally, the anatomical analysis of phloem and stem tissues in finger lime and 'Valencia' suggested better regeneration of phloem tissues in finger lime in response to HLB infection. Analysis of callose formation following infection revealed a significant difference in the production of callose plugs between the stem phloem of CaLas+ 'Valencia' sweet orange and finger lime. Understanding the mechanism of resistance will help the scientific community design strategies to protect trees from CaLas infection and assist citrus breeders in developing durable HLB tolerant citrus varieties. [ABSTRACT FROM AUTHOR]

The Australian finger lime (Citrus australasica) is tolerant to Huanglongbing (HLB; Citrus greening). This species can be utilized to develop HLB tolerant citrus cultivars through conventional breeding and biotechnological approaches. In this report, we conducted a comprehensive analysis of transcriptomic data following a non-choice infection assay to understand the CaLas tolerance mechanisms in the finger lime. After filtering 3,768 differentially expressed genes (DEGs), 2,396 were downregulated and 1,372 were upregulated in CaLas-infected finger lime compared to CaLas-infected HLB-susceptible ‘Valencia’ sweet orange. Comparative analyses revealed several DEGs belonging to cell wall, β-glucanase, proteolysis, R genes, signaling, redox state, peroxidases, glutathione-S-transferase, secondary metabolites, and pathogenesis-related (PR) proteins categories. Our results indicate that the finger lime has evolved specific redox control systems to mitigate the reactive oxygen species and modulate the plant defense response. We also identified candidate genes responsible for the production of Cys-rich secretory proteins and Pathogenesis-related 1 (PR1-like) proteins that are highly upregulated in infected finger lime relative to noninfected and infected ‘Valencia’ sweet orange. Additionally, the anatomical analysis of phloem and stem tissues in finger lime and ‘Valencia’ suggested better regeneration of phloem tissues in finger lime in response to HLB infection. Analysis of callose formation following infection revealed a significant difference in the production of callose plugs between the stem phloem of CaLas+ ‘Valencia’ sweet orange and finger lime. Understanding the mechanism of resistance will help the scientific community design strategies to protect trees from CaLas infection and assist citrus breeders in developing durable HLB tolerant citrus varieties.

Plant hormone brassinosteroids (BRs) play key roles in plant adaptation to biotic stresses, including various pathogen infections. As a core factor in BR signaling, the transcription factor BRI1-EMS-SUPPRESSOR 1 (BES1) activates BR responses via regulating the expression of target genes. However, the molecular mechanism of BRs in regulating plant immunity is unclear, and the key components are not identified. In this study, we found that BR biosynthesis and signaling transduction are essential for plant resistance to pathogen infection, and BR biosynthesis or BR signaling-deficient mutants displayed susceptibility to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) infection [including more serious symptoms and more photosystem II (PSII) photochemistry damage]. We identified a callose synthase gene GLUCAN SYNTHASE-LIKE 8 (GSL8) as a direct target of BES1, and its expression was induced by BRs/BES1. Meanwhile, BRs induced callose accumulation after Pst DC3000 infection. Moreover, BES1 gain-of-function mutant bes1-D showed promoted Pst DC3000 resistance. GSL8 T-DNA insertion mutant gsl8-1 was susceptible to DC3000, while brassinolide (BL) treatment partially rescued gsl8-1 susceptible phenotypes. Our study suggests that BR-induced pathogen resistance partly depends on the BR-induced BES1-GSL8 cascade to mediate callose accumulation. [ABSTRACT FROM AUTHOR]

Validamycin A (VMA) is an aminoglycoside antibiotic used to control rice sheath blight. Although it has been reported that VMA can induce the plant defense responses, the mechanism remains poorly understood. Here, we found that reactive oxygen species (ROS) bursts and callose deposition in Arabidopsis thaliana, rice (Oryza sativa L.), and wheat (Triticum aestivum L.) were induced by VMA and were most intense with 10 μg of VMA per milliliter at 24 h. Moreover, we showed that VMA induced resistance against Pseudomonas syringae, Botrytis cinerea, and Fusarium graminearum in Arabidopsis leaves, indicating that VMA induces broad-spectrum disease resistance in both dicots and monocots. In addition, VMA-mediated resistance against P. syringae was not induced in NahG transgenic plants, was partially decreased in npr1 mutants, and VMA-mediated resistance to B. cinerea was not induced in npr1, jar1, and ein2 mutants. These results strongly indicated that VMA triggers plant defense responses to both biotrophic and necrotrophic pathogens involved in salicylic acid (SA) and jasmonic acid/ethylene (JA/ET) signaling pathways and is dependent on NPR1. In addition, transcriptome analysis further revealed that VMA regulated the expression of genes involved in SA, JA/ET, abscisic acid (ABA), and auxin signal pathways. Taken together, VMA induces systemic resistance involving in SA and JA/ET signaling pathways and also exerts a positive influence on ABA and auxin signaling pathways. Our study highlights the creative application of VMA in triggering plant defense responses against plant pathogens, providing a valuable insight into applying VMA to enhance plant resistance and reduce the use of chemical pesticides.[Graphic: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

ABSTRACT Beneficial microorganisms need to overcome the plant defense system to establish on or within plant tissues. Like pathogens, beneficial microbes can manipulate a plant’s immunity pathways, first by suppressing and hiding to establish on the host and then by inducing resistance to protect the plant. In the current study, we demonstrated that although Pseudozyma aphidis can activate microbe-associated molecular pattern (MAMP)-associated genes, it does not activate MAMP-triggered callose deposition and can, moreover, suppress such deposition triggered by Flg22 or chitin. While MAMP-associated gene activation by P. aphidis was not dependent on salicylic acid, jasmonic acid, or ethylene signaling, suppression of MAMP-triggered callose deposition required the salicylic acid and jasmonic acid signaling factors JAR1-1 and E3 ubiquitin ligase COI1 yet did not rely on EIN2, NPR1, or the transcription factor JIN1/MYC2. We also demonstrated the ability of P. aphidis, known to be an epiphytic yeast-like organism, to penetrate the stomata and establish within plant tissues, as do endophytes. These results thus demonstrate the potential of P. aphidis to suppress MAMP-elicited defenses in order to establish on and within host plant tissues. IMPORTANCE Our study demonstrates the ability of P. aphidis to penetrate into plant tissues, where it avoids and overcomes plant defense systems in order to establish and subsequently protect the plant.

Plant hormone brassinosteroids (BRs) play key roles in plant adaptation to biotic stresses, including various pathogen infections. As a core factor in BR signaling, the transcription factor BRI1-EMS-SUPPRESSOR 1 (BES1) activates BR responses via regulating the expression of target genes. However, the molecular mechanism of BRs in regulating plant immunity is unclear, and the key components are not identified. In this study, we found that BR biosynthesis and signaling transduction are essential for plant resistance to pathogen infection, and BR biosynthesis or BR signaling-deficient mutants displayed susceptibility to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) infection [including more serious symptoms and more photosystem II (PSII) photochemistry damage]. We identified a callose synthase gene GLUCAN SYNTHASE-LIKE 8 (GSL8) as a direct target of BES1, and its expression was induced by BRs/BES1. Meanwhile, BRs induced callose accumulation after Pst DC3000 infection. Moreover, BES1 gain-of-function mutant bes1-D showed promoted Pst DC3000 resistance. GSL8 T-DNA insertion mutant gsl8-1 was susceptible to DC3000, while brassinolide (BL) treatment partially rescued gsl8-1 susceptible phenotypes. Our study suggests that BR-induced pathogen resistance partly depends on the BR-induced BES1-GSL8 cascade to mediate callose accumulation.

After perception of specific biotic or abiotic stimuli, such as root colonization by rhizobacteria or selected chemicals, plants can enhance their basal resistance against pathogens. Due to its likely sustainability, this induced resistance will be valuable for disease management in agriculture. This study examined resistance against wheat leaf rust (Puccinia triticina) induced by Pseudomonas protegens CHA0 (CHA0) and ß-aminobutyric acid (BABA). Seed dressing with CHA0 reduced the number of sporulating pustules on leaves, and expression of resistance was visible as necrotic or chlorotic leaf flecks. Beneficial effect of CHA0 on wheat seedlings growth was observed in when they were challenged or not with leaf rust. BABA was tested at 10, 15 or 20 mM, and a dose-dependent reduction of leaf rust infections was observed with greatest protection at 20 mM. However, BABA treatment repressed plant growth at 20 mM. Balancing the BABA impact on plant growth and its protective capacity, 15 mM of the compound was selected as suitable to protect wheat seedlings against leaf rust, with the least impact on vegetative host growth. Histological aspects of the pathogen infection process was studied to understand mechanisms of behind the observed resistance. The pre-entry process was not affected by the two resistance inducers, but both treatments reduced fungus penetration and haustorium formation. Timing and amplitude of the resistance reactions were different after bacterial or chemical induction, leading to different levels of resistance. During fungal colonization of host tissues, high deposition of callose and accumulation of H2O2 in both CHA0- and BABA-treated plants indicated important contributions to resistance. [ABSTRACT FROM AUTHOR]

To successfully colonize the plants, the pathogenic microbes secrete a mass of effector proteins which manipulate host immunity. Apple valsa canker is a destructive disease caused by the weakly parasitic fungus Valsa mali. A previous study indicated that the V. mali effector protein 1 (VmEP1) is an essential virulence factor. However, the pathogenic mechanism of VmEP1 in V. mali remains poorly understood. In this study, we found that the apple (Malus domestica) pathogenesis-related 10 proteins (MdPR10) are the virulence target of VmEP1 using a yeast two-hybrid screening. By bimolecular fluorescence (BiFC) and coimmunoprecipitation (Co-IP), we confirmed that the VmEP1 interacts with MdPR10 in vivo. Silencing of MdPR10 notably enhanced the V. mali infection, and overexpression of MdPR10 markedly reduced its infection, which corroborates its positive role in plant immunity against V. mali. Furthermore, we showed that the co-expression of VmEP1 with MdPR10 compromised the MdPR10-mediated resistance to V. mali. Taken together, our results revealed a mechanism by which a V. mali effector protein suppresses the host immune responses by interfering with the MdPR10-mediated resistance to V. mali during the infection.

Melon (Cucumis melo) is one of the top 10 fruits in the world, and its production often suffers due to soil-borne diseases. Grafting is an effective way to solve this problem. However, graft incompatibility between scion and rootstock limits the application of melon grafting. In this study, the melon was grafted onto eight Cucurbitaceae species (cucumber, pumpkin, melon, luffa, wax gourd, bottle gourd, bitter gourd, and watermelon), and graft compatibility evaluation and anatomical observation were conducted. Taking melon homo-grafted plants as control, melon grafted onto cucumber and pumpkin rootstocks was compatible, while melon grafted onto luffa, wax gourd, bottle gourd, bitter gourd, and watermelon rootstocks was incompatible based on the scion dry weight on day 42 after grafting. Meanwhile, we found that starch–iodine staining of scion stem base is an index to predict graft compatibility earlier, on day 14 after grafting. Further, microsection observations showed that there was more cell proliferation at graft junction of melon hetero-grafted combinations; vascular reconnection occurred in all graft combinations. However, excess callose deposited at graft junction resulted in the blockage of photosynthate transport, thus, leading to starch accumulation in scion stem base, and finally graft incompatibility. In addition, undegraded necrotic layer fragments were observed at graft junctions of melon grafted onto incompatible bitter gourd and watermelon rootstocks. The above results provide clues for the selection and breeding of compatible Cucurbitaceae rootstocks of melon and demonstrate that starch accumulation in scion base and callose deposition at graft junction is associated with melon graft compatibility.

Huanglongbing (HLB) is presently a major threat to the citrus industry. Because of this disease, millions of trees are currently dying worldwide. The putative causal agent is a motile bacteria belonging to Candidatus Liberibacter spp., which is transmitted by psyllids. The bacteria is responsible for the synthesis of callose at the phloem sieve plate, leading to the obstruction of the pores that provide connections between adjacent sieve elements, thus limiting the symplastic transport of the sugars and starches synthesized in leaves to the other plant organs. The Persian triploid lime (Citrus latifolia) is one of the most HLB-tolerant citrus varieties, but the determinants associated with the tolerance are still unknown. HLB-infected diploid Mexican lime (Citrus aurantiifolia) and Persian lime were investigated. The leaf petiole was analyzed using scanning electron microscopy (SEM) to observe callose deposition at the phloem sieve plate. Leaf starch contents and detoxification enzyme activities were investigated. In the field, Persian lime leaves present more limited symptoms due to HLB than the Mexican lime leaves do. Photosynthesis, stomatal conductance, and transpiration decreased compared with control plants, but values remained greater in the Persian than in the Mexican lime. Analysis of the petiole sieve plate in control petiole samples showed that pores were approximately 1.8-fold larger in the Persian than in the Mexican lime. SEM analyses of petiole samples of symptomatic leaves showed the important deposition of callose into pores of Mexican and Persian limes, whereas biochemical analyses revealed better detoxification in Persian limes than in Mexican limes. Moreover, SEM analyses of infected petiole samples of asymptomatic leaves showed much larger callose depositions into the Mexican lime pores than in the Persian lime pores, whereas biochemical traits revealed much better behavior in Persian limes than in Mexican limes. Our results reveal that polyploids present specific behaviors associated with important physiological and biochemical determinants that may explain the better tolerance of the Persian lime against HLB compared with the Mexican lime.

Melon (Cucumis melo) is one of the top 10 fruits in the world, and its production often suffers due to soil-borne diseases. Grafting is an effective way to solve this problem. However, graft incompatibility between scion and rootstock limits the application of melon grafting. In this study, the melon was grafted onto eight Cucurbitaceae species (cucumber, pumpkin, melon, luffa, wax gourd, bottle gourd, bitter gourd, and watermelon), and graft compatibility evaluation and anatomical observation were conducted. Taking melon homo-grafted plants as control, melon grafted onto cucumber and pumpkin rootstocks was compatible, while melon grafted onto luffa, wax gourd, bottle gourd, bitter gourd, and watermelon rootstocks was incompatible based on the scion dry weight on day 42 after grafting. Meanwhile, we found that starch–iodine staining of scion stem base is an index to predict graft compatibility earlier, on day 14 after grafting. Further, microsection observations showed that there was more cell proliferation at graft junction of melon hetero-grafted combinations; vascular reconnection occurred in all graft combinations. However, excess callose deposited at graft junction resulted in the blockage of photosynthate transport, thus, leading to starch accumulation in scion stem base, and finally graft incompatibility. In addition, undegraded necrotic layer fragments were observed at graft junctions of melon grafted onto incompatible bitter gourd and watermelon rootstocks. The above results provide clues for the selection and breeding of compatible Cucurbitaceae rootstocks of melon and demonstrate that starch accumulation in scion base and callose deposition at graft junction is associated with melon graft compatibility. [ABSTRACT FROM AUTHOR]

To successfully colonize the plants, the pathogenic microbes secrete a mass of effector proteins which manipulate host immunity. Apple valsa canker is a destructive disease caused by the weakly parasitic fungus Valsa mali. A previous study indicated that the V. mali effector protein 1 (VmEP1) is an essential virulence factor. However, the pathogenic mechanism of VmEP1 in V. mali remains poorly understood. In this study, we found that the apple (Malus domestica) pathogenesis-related 10 proteins (MdPR10) are the virulence target of VmEP1 using a yeast two-hybrid screening. By bimolecular fluorescence (BiFC) and coimmunoprecipitation (Co-IP), we confirmed that the VmEP1 interacts with MdPR10 in vivo. Silencing of MdPR10 notably enhanced the V. mali infection, and overexpression of MdPR10 markedly reduced its infection, which corroborates its positive role in plant immunity against V. mali. Furthermore, we showed that the co-expression of VmEP1 with MdPR10 compromised the MdPR10 -mediated resistance to V. mali. Taken together, our results revealed a mechanism by which a V. mali effector protein suppresses the host immune responses by interfering with the MdPR10 -mediated resistance to V. mali during the infection. [ABSTRACT FROM AUTHOR]

Distant hybridization of cereals is often impaired by fertilization barriers. Haploid induction through intergeneric crossing is well developed in wheat but has not been successful in rice due to incompatibility issues. The present study was thus undertaken to identify fertilization barriers that hinder the compatibility of the rice cultivar Punjab Rice 121 with maize and pearl millet lines as pollinators. A total of 37,357 spikelets were pollinated, yielding 494 caryopses upon supplementation with auxins. The resultant caryopses, arising from true intergeneric crosses, lacked embryos. Imaging of the pollinated pistils at different intervals indicated that intense callose depositions block the release of generative nuclei to the ovule in these wide crosses. Rice spikelets pollinated with rice pollen (cis-generic crosses) exhibited positive indicators of fertilization reaction at the micropyle. While the cis-generic crosses initiated true caryopsis formation after 24 h, no comparative reaction was observed in the intergeneric crosses. The current survey underlines that the rice female gametophyte presents a strong pre-fertilization barrier to foreign pollen. This barrier may be modulated in the future by altering genotype and auxin combinations. [ABSTRACT FROM AUTHOR]

Huanglongbing (HLB) is presently a major threat to the citrus industry. Because of this disease, millions of trees are currently dying worldwide. The putative causal agent is a motile bacteria belonging to Candidatus Liberibacter spp., which is transmitted by psyllids. The bacteria is responsible for the synthesis of callose at the phloem sieve plate, leading to the obstruction of the pores that provide connections between adjacent sieve elements, thus limiting the symplastic transport of the sugars and starches synthesized in leaves to the other plant organs. The Persian triploid lime (Citrus latifolia) is one of the most HLB-tolerant citrus varieties, but the determinants associated with the tolerance are still unknown. HLB-infected diploid Mexican lime (Citrus aurantiifolia) and Persian lime were investigated. The leaf petiole was analyzed using scanning electron microscopy (SEM) to observe callose deposition at the phloem sieve plate. Leaf starch contents and detoxification enzyme activities were investigated. In the field, Persian lime leaves present more limited symptoms due to HLB than the Mexican lime leaves do. Photosynthesis, stomatal conductance, and transpiration decreased compared with control plants, but values remained greater in the Persian than in the Mexican lime. Analysis of the petiole sieve plate in control petiole samples showed that pores were approximately 1.8-fold larger in the Persian than in the Mexican lime. SEM analyses of petiole samples of symptomatic leaves showed the important deposition of callose into pores of Mexican and Persian limes, whereas biochemical analyses revealed better detoxification in Persian limes than in Mexican limes. Moreover, SEM analyses of infected petiole samples of asymptomatic leaves showed much larger callose depositions into the Mexican lime pores than in the Persian lime pores, whereas biochemical traits revealed much better behavior in Persian limes than in Mexican limes. Our results reveal that polyploids present specific behaviors associated with important physiological and biochemical determinants that may explain the better tolerance of the Persian lime against HLB compared with the Mexican lime. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine whether zinc phosphate treatments of tomato plants (Solanum lycopersicum L.) can attenuate bacterial speck disease severity through reduction of Pseudomonas syringae pv. tomato (Pst) growth in planta and induce morphological and biochemical plant defence responses. Tomato plants were treated with 10 ppm (25.90 µM) zinc phosphate and then spray inoculated with strain DAPP-PG 215, race 0 of Pst. Disease symptoms were recorded as chlorosis and/or necrosis per leaf (%) and as numbers of necrotic spots. Soil treatments with zinc phosphate protected susceptible tomato plants against Pst, with reductions in both disease severity and pathogen growth in planta. The reduction of Pst growth in planta combined with significantly higher zinc levels in zinc-phosphate-treated plants indicated direct antimicrobial toxicity of this microelement, as also confirmed by in vitro assays. Morphological (i.e. callose apposition) and biochemical (i.e., expression of salicylic-acid-dependent pathogenesis-related protein PR1b1 gene) defence responses were induced by the zinc phosphate treatment, as demonstrated by histochemical and qPCR analyses, respectively. In conclusion, soil treatments with zinc phosphate can protect tomato plants against Pst attacks through direct antimicrobial activity and induction of morphological and biochemical plant defence responses. [ABSTRACT FROM AUTHOR]

Plants rely on autophagy and membrane trafficking to tolerate stress, combat infections, and maintain cellular homeostasis. However, the molecular interplay between autophagy and membrane trafficking is poorly understood. Using an AI-assisted approach, we identified Rab3GAP-like (Rab3GAPL) as a key membrane trafficking node that controls plant autophagy negatively. Rab3GAPL suppresses autophagy by binding to ATG8, the core autophagy adaptor, and deactivating Rab8a, a small GTPase essential for autophagosome formation and defense-related secretion. Rab3GAPL reduces autophagic flux in three model plant species, suggesting that its negative regulatory role in autophagy is conserved in land plants. Beyond autophagy regulation, Rab3GAPL modulates focal immunity against the oomycete pathogen Phytophthora infestans by preventing defense-related secretion. Altogether, our results suggest that Rab3GAPL acts as a molecular rheostat to coordinate autophagic flux and defense-related secretion by restraining Rab8a-mediated trafficking. This unprecedented interplay between a RabGAP-Rab pair and ATG8 sheds new light on the intricate membrane transport mechanisms underlying plant autophagy and immunity. • Rab3GAPL binds the core autophagic adaptor ATG8CL through a canonical AIM in plants • Rab3GAPL functions as a molecular rheostat in adjusting both autophagy and immunity • Rab3GAPL negatively regulates autophagy and immunity by limiting Rab8a trafficking • The interplay between Rab3GAPL and Rab8a controls defense secretion upon infection Yuen et al. reveal the negative regulatory role of Rab3GAPL in plant autophagy and immunity, where it acts as a rheostat, modulating membrane trafficking. Rab3GAPL controls autophagy by binding ATG8 and regulating Rab8a. Independent of its interaction with ATG8, Rab3GAPL also suppresses defense secretion mediated by Rab8a during pathogen infection. [ABSTRACT FROM AUTHOR]

Abstract Background Food contamination with Salmonella enterica and enterohemorrhagic Escherichia coli is among the leading causes of foodborne illnesses worldwide and crop plants are associated with > 50% of the disease outbreaks. However, the mechanisms underlying the interaction of these human pathogens with plants remain elusive. In this study, we have explored plant resistance mechanisms against these enterobacteria and the plant pathogen Pseudomonas syringae pv. tomato (Pst) DC3118, as an opportunity to improve food safety. Results We found that S. enterica serovar Typhimurium (STm) transcriptionally modulates stress responses in Arabidopsis leaves, including induction of two hallmark processes of plant defense: ROS burst and cell wall modifications. Analyses of plants with a mutation in the potentially STm-induced gene EXO70H4 revealed that its encoded protein is required for stomatal defense against STm and E. coli O157:H7, but not against Pst DC3118. In the apoplast however, EXO70H4 is required for defense against STm and Pst DC3118, but not against E. coli O157:H7. Moreover, EXO70H4 is required for callose deposition, but had no function in ROS burst, triggered by all three bacteria. The salicylic acid (SA) signaling and biosynthesis proteins NPR1 and ICS1, respectively, were involved in stomatal and apoplastic defense, as well as callose deposition, against human and plant pathogens. Conclusions The results show that EXO70H4 is involved in stomatal and apoplastic defenses in Arabidopsis and suggest that EXO70H4-mediated defense play a distinct role in guard cells and leaf mesophyll cells in a bacteria-dependent manner. Nonetheless, EXO70H4 contributes to callose deposition in response to both human and plant pathogens. NPR1 and ICS1, two proteins involved in the SA signaling pathway, are important to inhibit leaf internalization and apoplastic persistence of enterobacteria and proliferation of phytopathogens. These findings highlight the existence of unique and shared plant genetic components to fight off diverse bacterial pathogens providing specific targets for the prevention of foodborne diseases.

Rice gall dwarf virus (RGDV) and its leafhopper vector Recilia dorsalis are plant phloem-inhabiting pests. Currently, how the delivery of plant viruses into plant phloem via piercing-sucking insects modulates callose deposition to promote viral transmission remains poorly understood. Here, we initially demonstrated that nonviruliferous R. dorsalis preferred feeding on RGDV-infected rice plants than viruliferous counterpart. Electrical penetration graph assay showed that viruliferous R. dorsalis encountered stronger physical barriers than nonviruliferous insects during feeding, finally prolonging salivary secretion and ingestion probing. Viruliferous R. dorsalis feeding induced more defense-associated callose deposition on sieve plates of rice phloem. Furthermore, RGDV infection significantly increased the cytosolic Ca2+ level in rice plants, triggering substantial callose deposition. Such a virus-mediated insect feeding behavior change potentially impedes insects from continuously ingesting phloem sap and promotes the secretion of more infectious virions from the salivary glands into rice phloem. This is the first study demonstrating that the delivery of a phloem-limited virus by piercing-sucking insects into the plant phloem activates the defense-associated callose deposition to enhance viral transmission.

Rice gall dwarf virus (RGDV) and its leafhopper vector Recilia dorsalis are plant phloem-inhabiting pests. Currently, how the delivery of plant viruses into plant phloem via piercing-sucking insects modulates callose deposition to promote viral transmission remains poorly understood. Here, we initially demonstrated that nonviruliferous R. dorsalis preferred feeding on RGDV-infected rice plants than viruliferous counterpart. Electrical penetration graph assay showed that viruliferous R. dorsalis encountered stronger physical barriers than nonviruliferous insects during feeding, finally prolonging salivary secretion and ingestion probing. Viruliferous R. dorsalis feeding induced more defense-associated callose deposition on sieve plates of rice phloem. Furthermore, RGDV infection significantly increased the cytosolic Ca2+ level in rice plants, triggering substantial callose deposition. Such a virus-mediated insect feeding behavior change potentially impedes insects from continuously ingesting phloem sap and promotes the secretion of more infectious virions from the salivary glands into rice phloem. This is the first study demonstrating that the delivery of a phloem-limited virus by piercing-sucking insects into the plant phloem activates the defense-associated callose deposition to enhance viral transmission. [ABSTRACT FROM AUTHOR]

On infection, plant‐parasitic nematodes establish feeding sites in roots from which they take up carbohydrates among other nutrients. Knowledge on how carbohydrates are supplied to the nematodes' feeding sites is limited. Here, gene expression analyses showed that RNA levels of OsSWEET11 to OsSWEET15 were extremely low in both Meloidogyne graminicola (Mg)‐caused galls and noninoculated roots. All the rice sucrose transporter genes, OsSUT1 to OsSUT5, were either down‐regulated in Mg‐caused galls compared with noninoculated rice roots or had very low transcript abundance. OsSUT1 was the only gene up‐regulated in galls, at 14 days postinoculation (dpi), after being highly down‐regulated at 3 and 7 dpi. OsSUT4 was down‐regulated at 3 dpi. No noticeable OsSUTs promoter activities were detected in Mg‐caused galls of pOsSUT1 to ‐5::GUS rice lines. Loading experiments with carboxyfluorescein diacetate (CFDA) demonstrated that symplastic connections exist between phloem and Mg‐caused giant cells (GCs). According to data from OsGNS5‐ and OsGSL2‐overexpressing rice plants that had decreased and increased callose deposition, respectively, callose negatively affected Mg parasitism and sucrose supply to Mg‐caused GCs. Our results suggest that plasmodesmata‐mediated sucrose transport plays a pivotal role in sucrose supply from rice root phloem to Mg‐caused GCs, and OsSWEET11 to ‐15 and OsSUTs are not major players in it, although further functional analysis is needed for OsSUT1 and OsSUT4. [ABSTRACT FROM AUTHOR]

Copper ions (Cu2+) are key constituents of copper-based antimicrobial compounds (CBACs), which are extensively used in agriculture. Previously, we demonstrated that a low concentration of Cu2+ induced plant defenses associated with callose deposition in Arabidopsis as well as flg22, a microbe-associated molecular pattern (MAMP) peptide. However, the details and differences of the mechanisms between Cu2+- and flg22-mediated callose deposition remain unclear. Here, we reported that Cu2+- and flg22-induced defense responses and callose deposition are dependent on AtACS8 and AtACS2/AtACS6, respectively. After the RNA sequencing data were mined, the expression of MYB51 , MYB122 , CYP79B2 / B3 and CYP83B1 implied that a conserved downstream indole glucosinolate (IGS) metabolic pathway is regulated by Cu2+. In the Cu2+-induced response, the ethylene biosynthesis rate-limiting gene AtACS8 and the signal transduction pathway were found to be required for Cu2+-activated MYB51 and MYB122 transcription. Functional redundancy of MYB51 and MYB122, the key regulators of the IGS metabolic pathway, was identified in the Cu2+-mediated regulation of IGS gene transcription, promotion of callose deposition, and increase in Arabidopsis resistance to bacterial pathogens. Furthermore, IGS genes such as CYP79B2 , CYP81F2 and PAD2 were required for Cu2+-induced callose deposition and defense responses. Our results demonstrate that Cu2+ activates MYB51 and MYB122 through distinct ethylene signal transduction to regulate the IGS metabolic pathway, resulting in an enhanced defense response in Arabidopsis. • Cu2+ triggers a MAMP-triggered-immunity-like indole glucosinolate (IGS) metabolic pathway. • Cu2+-induced callose deposition is specifically dependent on ACS8. • MYB51 and MYB122 are required to Cu2+-induced callose deposition. [ABSTRACT FROM AUTHOR]

Avocado (Persea americana) is an economically important fruit crop world-wide, the production of which is challenged by notable root pathogens such as Phytophthora cinnamomi and Rosellinia necatrix. Arguably the most prevalent, P. cinnamomi, is a hemibiotrophic oomycete which causes Phytophthora root rot, leading to reduced yields and eventual tree death. Despite its’ importance, the development of molecular tools and resources have been historically limited, prohibiting significant progress toward understanding this important host-pathogen interaction. The development of a nested qPCR assay capable of quantifying P. cinnamomi during avocado infection has enabled us to distinguish avocado rootstocks as either resistant or tolerant - an important distinction when unraveling the defense response. This review will provide an overview of our current knowledge on the molecular defense pathways utilized in resistant avocado rootstock against P. cinnamomi. Notably, avocado demonstrates a biphasic phytohormone profile in response to P. cinnamomi infection which allows for the timely expression of pathogenesis-related genes via the NPR1 defense response pathway. Cell wall modification via callose deposition and lignification have also been implicated in the resistant response. Recent advances such as composite plant transformation, single nucleotide polymorphism (SNP) analyses as well as genomics and transcriptomics will complement existing molecular, histological, and biochemical assay studies and further elucidate avocado defense mechanisms.

Avocado (Persea americana) is an economically important fruit crop world-wide, the production of which is challenged by notable root pathogens such as Phytophthora cinnamomi and Rosellinia necatrix. Arguably the most prevalent, P. cinnamomi , is a hemibiotrophic oomycete which causes Phytophthora root rot, leading to reduced yields and eventual tree death. Despite its' importance, the development of molecular tools and resources have been historically limited, prohibiting significant progress toward understanding this important host-pathogen interaction. The development of a nested qPCR assay capable of quantifying P. cinnamomi during avocado infection has enabled us to distinguish avocado rootstocks as either resistant or tolerant - an important distinction when unraveling the defense response. This review will provide an overview of our current knowledge on the molecular defense pathways utilized in resistant avocado rootstock against P. cinnamomi. Notably, avocado demonstrates a biphasic phytohormone profile in response to P. cinnamomi infection which allows for the timely expression of pathogenesis-related genes via the NPR1 defense response pathway. Cell wall modification via callose deposition and lignification have also been implicated in the resistant response. Recent advances such as composite plant transformation, single nucleotide polymorphism (SNP) analyses as well as genomics and transcriptomics will complement existing molecular, histological, and biochemical assay studies and further elucidate avocado defense mechanisms. [ABSTRACT FROM AUTHOR]

Abstract Background Members of the WRKY gene family play important roles in regulating plant responses to abiotic and biotic stresses. Treatment with either one of the two different cell wall degrading enzymes (CWDEs), LipaseA and CellulaseA, induces immune responses and enhances the expression of OsWRKY42 in rice. However, the role of OsWRKY42 in CWDE induced immune responses is not known. Results Expression of the rice transcription factor OsWRKY42 is induced upon treatment of rice leaves with CWDEs, wounding and salt. Overexpression of OsWRKY42 leads to enhanced callose deposition in rice and Arabidopsis but this does not enhance tolerance to bacterial infection. Upon treatment with NaCl, Arabidopsis transgenic plants expressing OsWRKY42 exhibited high levels of anthocyanin and displayed enhanced tolerance to salt stress. Treatment with either cellulase or salt induced the expression of several genes involved in JA biosynthesis and response in Arabidopsis. Ectopic expression of OsWRKY42 results in reduced expression of cell wall damage and salt stress induced jasmonic acid biosynthesis and response genes. OsWRKY42 expressing Arabidopsis lines exhibited enhanced tolerance to methyl jasmonate mediated growth inhibition. Conclusion The results presented here suggest that OsWRKY42 regulates plant responses to either cell wall damage or salinity stress by acting as a negative regulator of jasmonic acid mediated responses.

Key message: The appropriate combination of fluorescent probes enabled the simultaneous visualization of callose deposition and plasma membrane in living Arabidopsis and can be useful for the cell biological study of papilla formation in plants. Localized callose deposition at the site of fungal infection is a central part of papilla formation, which creates a barrier between the host plasma membrane and the cell wall and plays an important role in preventing the penetration of fungal hyphae into the host cells. Using chitin-induced callose deposition as a model system, we examined suitable conditions for the simultaneous visualization of callose deposition and plasma membrane dynamics in living Arabidopsis cotyledons. We found that aniline blue fluorochrome (ABF) for callose staining selectively interferes with FM dyes for membrane visualization depending on the structure of the latter compounds and the proper combination of these fluorescent dyes and staining conditions is a key for successful live-cell imaging. The established conditions enabled the live-cell imaging of chitin-induced callose deposition and host membrane systems. The established system/conditions would also be useful for the cell biological studies on the localized callose deposition in other stress/development-associated processes. The finding that the slight difference in the structure of FM dyes affects the interaction with another fluorescent dye, ABF, would also give useful suggestions for the studies where multiple fluorescent dyes are utilized for live-cell imaging. [ABSTRACT FROM AUTHOR]

We isolated a new Trichoderma harzianum strain, named T-A66. Potato dextrose agar (PDA) was the best medium for both mycelium growth and sporulation of T-A66 strain, while sucrose and potassium nitrate were the best source of carbon and nitrate, respectively. T-A66 strain and its culture filtrate significantly antagonized the growth of the pathogen Fusarium oxysporum in in vitro tests. An experiment using potted plants showed that the T-A66 strain promoted growth and induced disease resistance of bitter gourd seedlings to bitter gourd wilt caused by F. oxysporum, by inducing quick H2 O2 burst and callose deposition, as well as increasing antioxidant enzymes activities and phenolic compounds content. Indole acetic acid (IAA) was involved in the beneficial effects of T-A66. Ultimately, T-A66 strain diminished membrane lipid peroxidation and cell death, and controlled successfully bitter gourd wilt in greenhouse with a biocontrol efficiency of 90.32% after 15 days of F. oxysporum inoculation. The results suggested a good biocontrol potential of T-A66 strain against bitter gourd wilt. [ABSTRACT FROM AUTHOR]

Bacterial wilt (BW) is a serious disease that affects potato (Solanum tuberosum L.) production. Although resistance to this disease has been reported, the underlying mechanism is unknown. In this study, we identified a NAC family transcription factor (StNACb4) from potato and characterised its structure, function, expression, its localisation at the tissue and its role in BW resistance. To this end, the transgenic Nicotiana benthamiana Domin lines were generated in which the expression of NACb4 was constitutively upregulated or suppressed using RNAi. Different tobacco mutants were stained after inoculating with Ralstonia solanacearum to observe the cell death and callose deposition. The results indicated that StNACb4 could be upregulated under the induction of R. solanacearum, and salicylic acid, abscisic acid and methyl jasmonate could also induce the expression of StNACb4. Tissue localisation analysis indicated that its expression was tissue specific, and it was mainly in the phloem of the vascular system of stems and leaves. NbNACb4 gene silencing can enhance the sensitivity of tobacco to R. solanacearum; on the contrary, StNACb4 gene overexpression can enhance the tolerance of tobacco to R. solanacearum. Meanwhile, StNACb4 gene overexpression can induce cell death and callose deposition in tobacco. The upregulated expression of StNACb4 can also activate the StPR10 gene expression. Our results provide important new insights into the regulatory mechanisms of bacterial wilt resistance in potato. [ABSTRACT FROM AUTHOR]

Plants exposed to the combination of drought and pathogen infections are in a unique state, different from that of plants exposed to each stress alone. Plants undergo major hormonal changes during drought and/or pathogen infection, highlighting the importance of hormones as crucial mediators of plant stress responses. Evidence from individual stress studies has shown that drought and pathogen infection have both different and overlapping impacts on hormone metabolism and hormone-associated signal transduction pathways. Thus, under the combination of drought and pathogen infection, a reprograming of hormone levels and related signaling networks is inevitable. This process delivers data from plants exposed to individual stressors inadequate for predicting how hormone levels and related signaling networks will change in plants exposed to a combination of stressors. Furthermore, the yield of crop plants, determined by their capacity for stress acclimatization and resistance to pathogen infection, will be underpinned by interactions among the hormone pathways. Although many studies have been conducted to understand the molecular mechanisms associated with plant responses to combinations of stressors, the interactions that occur among hormones are far from being well-understood. We provide here an overview and evaluation of various reports on crosstalk or overlapping hormonal responses from individual stress studies and how the combination of drought and pathogen infection modulates hormone levels and their associated signaling pathways in plant responses to these combined stresses. We also give a brief overview of the importance of overlapping plant responses for the production of crop plants resistant to individual and combined stressors under natural environmental conditions. [ABSTRACT FROM AUTHOR]

Pathogen secreted cell-wall-degrading enzymes (CWDEs) induce plant innate immune responses. The expression of rice transcription factor APETALA2/ethylene response factor-152 (OsAP2/ERF152) is enhanced in leaves upon treatment with different CWDEs and upon wounding. Ectopic expression of OsAP2/ERF152 in Arabidopsis leads to induction of immune responses such as callose deposition and upregulation of both salicylic acid- and jasmonic acid/ethyleneresponsive defense genes. Arabidopsis transgenics expressing OsAP2/ ERF152 exhibited resistance to infections caused by both bacterial and fungal pathogens (Pseudomonas syringae pv. tomato DC3000 and Rhizoctonia solani AG1-IA, respectively). Ectopic expression of OsAP2/ ERF152 results in transient activation of mitogen-activated protein kinases 3/6 (MPK3/6), which could be leading to the induction of a broad range immunity in Arabidopsis. [ABSTRACT FROM AUTHOR]

The green peach aphid, Myzus persicae, is one of the most threatening pests in pepper cultivation and growers would benefit from resistant varieties. Previously, we identified two Capsicum accessions as susceptible and three as resistant to M. persicae using an aphid population originating from the Netherlands (NL). Later on we identified an aphid population originating from a different geographical region (Switserland, SW) that was virulent on all tested Capsicum accessions. The objective of the current work is to describe in detail different aspects of the interaction between two aphid populations and two selected Capsicum accessions (one that was susceptible [PB2013046] and one that was resistant [PB2013071] to population NL), including biochemical processes involved. Electrical penetration graph (EPG) recordings showed similar feeding activities for both aphid populations on PB2013046. On accession PB2013071 the aphid population SW was able to devote significantly more time to phloem ingestion than population NL. We also studied plant defense response and found that plants of accession PB2013046 could not induce an accumulation of reactive oxygen species and callose formation after infestation with either aphid population. However, plants of PB2013071 induced a stronger defense response after infestation by population NL than after infestation by population SW. Based on these results, population SW of M. persicae seems to have overcome the resistance of PB2013071 that prevented feeding of aphids from NL population. The potential mechanism by which SW population overcomes the resistance is discussed. [ABSTRACT FROM AUTHOR]

Benzoxazinoids are important secondary metabolites in gramineae plants and have inhibitory and toxic effects against a wide range of herbivore pests. However, the relationship between benzoxazinoid level and plant resistance to aphids remains controversial. In this study, we investigated the relationship between benzoxazinoids composition and concentration in wheat leaves and the resistance to the grain aphid Sitobion avenae. Overall, six benzoxazinoids were detected and identified by mass spectrometry based metabolites profiling, including three lactams, two hydroxamic acids, and one methyl derivative. The constitutive levels of these benzoxazinoids were significantly different among the wheat varieties/lines. However, none of these benzoxazinoids exhibited considerable correlation with aphid resistance. S. avenae feeding elevated the level of 2-O-β-D-glucopyranosyloxy-4,7-dimethoxy-(2H)-1,4-benzoxazin-3(4H)-one (HDMBOA-Glc) and reduced the level of 2-O-β-D-glucopyranosyloxy-4-hydroxy-7-(2H)-methoxy-1,4-benzoxazin-3(4H)-one (DIMBOA-Glc) in some of the wheat varieties/lines. Moreover, aphid-induced level of DIMBOA-Glc was positively related with callose deposition, which was closely associated with aphid resistance. Wheat leaves infiltrated with DIMBOA-Glc caused a noticeable increase of callose deposition and the effect was in a dose dependent manner. This study suggests that the constitutive level of benzoxazinoids has limited impact on S. avenae. Aphid feeding can affect the balance of benzoxazinoids metabolism and the dynamic level of benzoxazinoids can act as a signal of callose deposition for S. avenae resistance. This study will extend our understanding of aphid–wheat interaction and provides new insights in aphid-resistance wheat breeding.