ET-signaling Pathway Research Articles

Identification and Characterization of High-Molecular-Weight Proteins Secreted by Plasmodiophora brassicae That Suppress Plant Immunity.

Plasmodiophora brassicae is an obligate intracellular parasitic protist that causes clubroot disease on cruciferous plants. So far, some low-molecular-weight secreted proteins from P. brassicae have been reported to play an important role in plant immunity regulation, but there are few reports on its high-molecular-weight secreted proteins. In this study, 35 putative high-molecular-weight secreted proteins (>300 amino acids) of P. brassicae (PbHMWSP) genes that are highly expressed during the infection stage were identified using transcriptome analysis and bioinformatics prediction. Then, the secretory activity of 30 putative PbHMWSPs was confirmed using the yeast signal sequence trap system. Furthermore, the genes encoding 24 PbHMWSPs were successfully cloned and their functions in plant immunity were studied. The results showed that ten PbHMWSPs could inhibit flg22-induced reactive oxygen burst, and ten PbHMWSPs significantly inhibited the expression of the SA signaling pathway marker gene PR1a. In addition, nine PbHMWSPs could inhibit the expression of a marker gene of the JA signaling pathway. Therefore, a total of 19 of the 24 tested PbHMWSPs played roles in suppressing the immune response of plants. Of these, it is worth noting that PbHMWSP34 can inhibit the expression of JA, ET, and several SA signaling pathway marker genes. The present study is the first to report the function of the high-molecular-weight secreted proteins of P. brassicae in plant immunity, which will enrich the theory of interaction mechanisms between the pathogens and plants.

Tomato CYP94C1 inactivates bioactive JA-Ile to attenuate jasmonate-mediated defense during fruit ripening

As the master regulators of the ET signaling pathway, EIL transcription factors directly activate the expression of CYP94C1 to inactivate bioactive JA-Ile, thereby attenuating JA-mediated defense during fruit ripening. Knockout of CYP94C1 improves tomato fruit resistance to necrotrophs without compromising fruit quality.

Ethylene enhanced waterlogging tolerance by changing root architecture and inducing aerenchyma formation in maize seedlings

Waterlogging negatively affects maize growth and yield. In this study, we found that ethylene played a vital role in plant adaptation to waterlogging. ET promotes better growth in seedlings under waterlogging conditions by altering root architecture and increasing lateral root formation by 42.1%. What's more, plants with high endogenous ethylene levels exhibited reduced sensitivity to waterlogging stress. ET also induced the formation of aerenchyma, a specialized tissue that facilitates gas exchange, in a different pattern compared to aerenchyma formed under waterlogging. Aerenchyma induced by ET was mainly located in the medial cortex of the roots and was not prone to decay. ethylene inhibited root elongation under normal conditions, but this inhibition was not alleviated under waterlogging stress. Upon activation of the ET signaling pathway, the transcription factor EREB90 promoted aerenchyma formation by enhancing the programmed cell death process. Overexpression of EREB90 resulted in increased waterlogging tolerance compared to wild type plants. Our findings suggest that pre-treatment of maize seedlings with ET before waterlogging stress can trigger the programmed cell death process and induce aerenchyma formation, thus improving waterlogging resistance.

Transcriptomic and physiological analysis reveals the possible mechanism of ultrasound inhibiting strawberry (Fragaria × ananassa Duch.) postharvest softening.

Ultrasound effectively inhibited strawberry softening but the mechanism was not clear. In this study, physical data including firmness, soluble pectin (SP) contents, pectin esterase (PE), polygalacturonase (PG) activity and transcriptome sequencing data were analyzed to explore the mechanism of strawberry response to ultrasonic treatment. After 24 days storage, the firmness reduction rate and soluble contents (SP) increased rate of the strawberry treated with ultrasound (25 kHz, 0.15 W/cm2) for 3 min decreased 41.70 and 63.12% compared with the control, respectively. While the PG and PE enzyme activities of ultrasound-treated strawberries were significantly lower than control after storage for 18 days. A total of 1,905 diferentially expressed genes (DEGs) were identified between ultrasound-treated and control, with 714 genes upregulated and 1,254 genes downregulated, including 56 genes in reactive oxygen species (ROS), auxin (AUX), ethylene (ETH) and jasmonic acid (JA) signaling pathways. At 0 h, 15 genes including LOX, JMT, ARP, SKP, SAUR, IAA, ARF, and LAX were significantly upregulated compared with the control group, which means reactive oxygen specie, auxin, ethylene and jasmonic acid-mediated signaling pathway respond to ultrasound immediately. ERF109, ERF110, and ACS1_2_6 downregulated before 2 days storage indicated ethylene signaling pathway was inhibited, while after 2 days, 9 genes including ERF027, ERF109, and ERF110 were significantly upregulated indicating that the response of the ethylene signaling pathway was lagging. Therefore, in strawberry ultrasound enhanced ROS scavenging and activated JA biosynthesis, which acts as a signal for delaying the activation of ET signaling pathway, thus suppressing the activity of pectin-degrading enzymes PE and PG, and ultimately inhibiting postharvest softening.

Immunomodulatory Molecular Mechanisms of Luffa cylindrica for Downy Mildews Resistance Induced by Growth-Promoting Endophytic Fungi.

Downy mildew (DM), caused by P. cubensis, is harmful to cucurbits including luffa, with increased shortcomings associated with its control through cultural practices, chemical fungicides, and resistant cultivars; there is a prompt need for an effective, eco-friendly, economical, and safe biocontrol approach. Current research is therefore dealt with the biocontrol of luffa DM1 through the endophytic fungi (EF) consortium. Results revealed that T. harzianum (ThM9) and T. virens (TvA1) showed pathogen-dependent inducible metabolic production of squalene and gliotoxins by higher gene expression induction of SQS1/ERG9 (squalene synthase) and GliP (non-ribosomal peptide synthetase). Gene expression of lytic enzymes of EF was also induced with subsequently higher enzyme activities upon confrontation with P. cubensis. EF-inoculated luffa seeds showed efficient germination with enhanced growth potential and vigor of seedlings. EF-inoculated plants showed an increased level of growth-promoting hormone GA with higher gene expression of GA2OX8. EF-pre-inoculated seedlings were resistant to DM and showed an increased GSH content and antioxidant enzyme activities (SOD, CAT, POD). The level of MDA, H2O2, REL, and disease severity was reduced by EF. ACC, JA, ABA, and SA were overproduced along with higher gene expression of LOX, ERF, NCED2, and PAL. Expression of defense-marker genes (PPO, CAT2, SOD, APX, PER5, LOX, NBS-LRR, PSY, CAS, Ubi, MLP43) was also modulated in EF-inoculated infected plants. Current research supported the use of EF inoculation to effectively escalate the systemic immunity against DM corresponding to the significant promotion of induced systemic resistance (ISR) and systemic acquired resistance (SAR) responses through initiating the defense mechanism by SA, ABA, ET, and JA biosynthesis and signaling pathways in luffa.

Arabinogalactan Protein-Like Proteins From Ulva lactuca Activate Immune Responses and Plant Resistance in an Oilseed Crop.

Natural compounds isolated from macroalgae are promising, ecofriendly, and multifunctional bioinoculants, which have been tested and used in agriculture. Ulvans, for instance, one of the major polysaccharides present in Ulva spp. cell walls, have been tested for their plant growth-promoting properties as well as their ability to activate plant immune defense, on a large variety of crops. Recently, we have characterized for the first time an arabinogalactan protein-like (AGP-like) from Ulva lactuca, which exhibits several features associated to land plant AGPs. In land plant, AGPs were shown to play a role in several plant biological functions, including cell morphogenesis, reproduction, and plant-microbe interactions. Thus, isolated AGP-like proteins may be good candidates for either the plant growth-promoting properties or the activation of plant immune defense. Here, we have isolated an AGP-like enriched fraction from Ulva lactuca and we have evaluated its ability to (i) protect oilseed rape (Brassica napus) cotyledons against Leptosphaeria maculans, and (ii) its ability to activate immune responses. Preventive application of the Ulva AGP-like enriched fraction on oilseed rape, followed by cotyledon inoculation with the fungal hemibiotroph L. maculans, resulted in a major reduction of infection propagation. The noticed reduction correlated with an accumulation of H2O2 in treated cotyledons and with the activation of SA and ET signaling pathways in oilseed rape cotyledons. In parallel, an ulvan was also isolated from Ulva lactuca. Preventive application of ulvan also enhanced plant resistance against L. maculans. Surprisingly, reduction of infection severity was only observed at high concentration of ulvan. Here, no such significant changes in gene expression and H2O2 production were observed. Together, this study indicates that U. lactuca AGP-like glycoproteins exhibit promising elicitor activity and that plant eliciting properties of Ulva extract, might result not only from an ulvan-originated eliciting activities, but also AGP-like originated.

Wheat transcriptome profiling reveals abscisic and gibberellic acid treatments regulate early-stage phytohormone defense signaling, cell wall fortification, and metabolic switches following Fusarium graminearum-challenge

BackgroundTreatment of wheat with the phytohormones abscisic acid (ABA) and gibberellic acid (GA) has been shown to affect Fusarium head blight (FHB) disease severity. However, the molecular mechanisms underlying the elicited phenotypes remain unclear. Toward addressing this gap in our knowledge, global transcriptomic profiling was applied to the FHB-susceptible wheat cultivar ‘Fielder’ to map the regulatory responses effected upon treatment with ABA, an ABA receptor antagonist (AS6), or GA in the presence or absence of Fusarium graminearum (Fg) challenge.ResultsSpike treatments resulted in a total of 30,876 differentially expressed genes (DEGs) identified in ‘Fielder’ (26,004) and the Fg (4872) pathogen. Topology overlap and correlation analyses defined 9689 wheat DEGs as Fg-related across the treatments. Further enrichment analyses demonstrated that these included expression changes within ‘Fielder’ defense responses, cell structural metabolism, molecular transport, and membrane/lipid metabolism. Dysregulation of ABA and GA crosstalk arising from repression of ‘Fielder’ FUS3 was noted. As well, expression of a putative Fg ABA-biosynthetic cytochrome P450 was detected. The co-applied condition of Fg + ABA elicited further up-regulation of phytohormone biosynthesis, as well as SA and ET signaling pathways and cell wall/polyphenolic metabolism. In contrast, co-applied Fg + GA mainly suppressed phytohormone biosynthesis and signaling, while modulating primary and secondary metabolism and flowering. Unexpectedly, co-applied Fg + AS6 did not affect ABA biosynthesis or signaling, but rather elicited antagonistic responses tied to stress, phytohormone transport, and FHB disease-related genes.ConclusionsObserved exacerbation (misregulation) of classical defense mechanisms and cell wall fortifications upon ABA treatment are consistent with its ability to promote FHB severity and its proposed role as a fungal effector. In contrast, GA was found to modulate primary and secondary metabolism, suggesting a general metabolic shift underlying its reduction in FHB severity. While AS6 did not antagonize traditional ABA pathways, its impact on host defense and Fg responses imply potential for future investigation. Overall, by comparing these findings to those previously reported for four additional plant genotypes, an additive model of the wheat-Fg interaction is proposed in the context of phytohormone responses.

Bacillus velezensis CLA178-Induced Systemic Resistance of Rosa multiflora Against Crown Gall Disease.

Plant growth-promoting rhizobacteria (PGPRs) are able to activate induced systemic resistance (ISR) of the plants against phytopathogens. However, whether and how ISR can be activated by PGPRs in plants of the Rosa genus is unclear. The effects of PGPR Bacillus velezensis CLA178 and the pathogen Agrobacterium tumefaciens C58 on the growth, plant defense-related genes, hormones, and reactive oxygen species (ROS) in the rose plants were compared. Pretreatment with CLA178 significantly reduced crown gall tumor biomass and relieved the negative effects of the C58 pathogen on plant biomass, chlorophyll content, and photosynthesis of roses. Pretreatment of the roots with CLA178 activated ISR and significantly reduced disease severity. Pretreatment with CLA178 enhanced plant defense response to C58, including the accumulation of ROS, antioxidants, and plant hormones. Moreover, pretreatment with CLA178 enhanced C58-dependent induction of the expression of the genes related to the salicylic acid (SA) or ethylene (ET) signaling pathways. This result suggested that SA- and ET-signaling may participate in CLA178-mediated ISR in roses. Additional experiments in the Arabidopsis mutants showed that CLA178 triggered ISR against C58 in the pad4 and jar1 mutants and not in the etr1 and npr1 mutants. The ISR phenotypes of the Arabidopsis mutants indicated that CLA178-mediated ISR is dependent on the ET-signaling pathway in an NPR1-dependent manner. Overall, this study provides useful information to expand the application of PGPRs to protect the plants of the Rosa genus from phytopathogens.

Redox Status, JA and ET Signaling Pathway Regulating Responses to Botrytis cinerea Infection Between the Resistant Cucumber Genotype and Its Susceptible Mutant.

Botrytis cinerea is an important necrotrophic fungal pathogen with a broad host range and the ability to causing great economic losses in cucumber. However, the resistance mechanism against this pathogen in cucumber was not well understood. In this study, the microscopic observation of the spore growth, redox status measurements and transcriptome analysis were carried out after Botrytis cinerea infection in the resistant genotype No.26 and its susceptible mutant 26M. Results revealed shorter hypha, lower rate of spore germination, less acceleration of H2O2, O2 -, and lower total glutathione content (GSH+GSSG) in No.26 than that in 26M, which were identified by the staining result of DAB and NBT. Transcriptome data showed that after pathogen infection, a total of 3901 and 789 different expression genes (DEGs) were identified in No.26 and 26M respectively. These DEGs were highly enriched in redox regulation pathway, hormone signaling pathway and plant-pathogen interaction pathway. The glutathione S-transferase genes, putative peroxidase gene, and NADPH oxidase were up-regulated in No.26 whereas these genes changed little in 26M after Botrytis cinerea infection. Jasmonic acid and ethylene biosynthesis and signaling pathways were distinctively activated in No.26 comparing with 26M upon infection. Much more plant defense related genes including mitogen-activated protein kinases, calmodulin, calmodulin-like protein, calcium-dependent protein kinase, and WRKY transcription factor were induced in No.26 than 26M after pathogen infection. Finally, a model was established which elucidated the resistance difference between resistant cucumber genotype and susceptible mutant after B. cinerea infection.

Novel crosstalk between ethylene- and jasmonic acid-pathway responses to a piercing-sucking insect in rice.

Ethylene (ET) and jasmonic acid (JA) play important roles in plant defenses against biotic stresses. Crosstalk between JA and ET has been well studied in mediating pathogen resistance, but its roles in piercing-sucking insect resistance are unclear. The brown planthopper (BPH; Nilaparvata lugens) is the most notorious piercing-sucking insect specific to rice (Oryza sativa) that severely affects yield. A genetic analysis revealed that OsEBF1 and OsEIL1, which are in the ET signaling pathway, positively and negatively regulated BPH resistance, respectively. Molecular and biochemical analyses revealed direct interactions between OsEBF1 and OsEIL1. OsEBF1, an E3 ligase, mediated the degradation of OsEIL1 through the ubiquitination pathway, indicating the negative regulation of the ET-signaling pathway in response to BPH infestation. An RNA sequencing analysis revealed that a JA biosynthetic pathway-related gene, OsLOX9, was downregulated significantly in the oseil1 mutant. Biochemical analyses, including yeast one-hybrid, dual luciferase, and electrophoretic mobility shift assay, confirmed the direct regulation of OsLOX9 by OsEIL1. This study revealed the synergistic and negative regulation of JA and ET pathways in response to piercing-sucking insect attack. The synergistic mechanism was realized by transcriptional regulation of OsEIL1 on OsLOX9. OsEIL1-OsLOX9 is a novel crosstalk site in these two phytohormone signaling pathways.

Identification of the targets of HbEIN3/EILs in genomic wide in Hevea brasiliensis.

EIN3/EILs are key regulators in ET signaling pathway. In this work, 4 members of EIN3/EILs of Hevea brasiliensis (HbEIN3/EILs) showed interaction with two F box proteins, HbEBF1 and HbEBF2. HbEIN3 located in nucleus and exhibited strong transcriptional activity. HbEIN3 was induced by ET treatment in C-serum, but not in B-serum of latex. HbEIN3/EILs bound to G-box cis-element. To globally search the potential targets of HbEIN3/EILs, genomic sequences of H. brasiliensis was re-annotated and an HCES (Hevea Cis-Elements Scanning) program was developed ( www.h-brasiliensis.com ). HCES scanning results showed that ET- and JA- responsive cis-elements distribute overlapping in gene promoters. 3146 genes containing G-box in promoters are potential targets of HbEIN3, including 41 genes involved in biosynthesis and drainage of latex, of which 7 rate-limiting genes of latex production were regulated by both ET and JA, suggesting that ET and JA signaling pathways coordinated the latex biosynthesis and drainage in H. brasiliensis. Abbreviations: ABRE: ABA responsive elements; bHLH: basic helix-loop-helix; COG: Orthologous Groups; DRE: dehydration response element; ERE: ethylene responsive element; ET: Ethylene; GO: Gene Ontology; HCES: Hevea Cis-Elements Scanning; JA: jasmonates; JRE: Jasmonate-responsive element; KEGG: Kyoto Encyclopedia of Genes and Genomes; NR: non-redundant database; PLACE: Plant Cis-acting Regulatory DNA Elements; qRT-PCR: quantitative real-time RT-PCR.

Bioinoculants for Bioremediation Applications and Disease Resistance: Innovative Perspectives.

Soil microbial species that act as PGPR or bioinoculants have the capability of improving plant health and promoting its growth. They facilitate plants for uptake nutrients from their surroundings. They provide resistivity to pathogenic pests and also play many roles in the bioremediation process. Bioremediation is the biological approach for the elimination of toxic contaminants by the approach of beneficial microbes. By the consortium of beneficial microbes and plant, a large number of heavy metal and organic contaminants can be controlled. With this advancement of bioremediation, microbial species that act as bioinoculants also help in the enhancement of induced systemic resistance (ISR) and their consortium triggers it by controlling SA, JA, ET and hormonal signaling pathways. Here, this review discusses the progress made on these areas and how the beneficial microbes that act as bioinoculants towards triggering bioremediation and ISR mechanism.

Transcriptional evidence for cross talk between JA and ET or SA during root-knot nematode invasion in tomato.

studies have demonstrated that jasmonic acid (JA) reduces root-knot nematode (RKN) infections in tomato plants. RKN invasion is sensed by roots, and root-derived JA signaling activates systemic defense responses, though this is poorly understood. Here, we investigate variations in the RKN-induced transcriptome in scion phloem between two tomato plant grafts: CM/CM ( Lycopersicum esculentum Mill. cv. Castlemart) and CM/ spr2 (a JA-deficient mutant). A total of 8,716 genes were differentially expressed in the scion phloem of the plants with JA-deficient rootstock via RNA sequencing. Among these genes, 535 upregulated and 153 downregulated genes with high copy numbers were identified as significantly differentially expressed. Among them, 34 predicted transcription factor genes were identified. Additionally, we used real-time quantitative PCR to analyze the expression patterns of 42 genes involved in the JA, ethylene, or salicylic acid pathway in phloem under RKN infection. The results suggested that in the absence of JA signaling, the ET signaling pathway is enhanced after RKN infection; however, alterations in the SA signaling pathway were not observed.

Resistance of Fusarium poae in Arabidopsis leaves requires mainly functional JA and ET signaling pathways

Fusarium poae has been considered as a minor species among those that cause the FHB disease but in recent years several researchers have documented a high frequency of occurrence in several crops. We evaluated the ability of F. poae to produce symptoms in A. thaliana leaves. Moreover, we analyzed the defense of A. thaliana against F. poae using SA, JA, and ET mutants and we monitored the expression level of genes involved in the main signaling pathways related to plant defense. Symptoms were observed in the inoculated leaves demonstrating the ability of F. poae to infect A. thaliana leaves. Moreover, the npr1-1 mutants presented low symptoms compared to Col-0, etr2-1, and coi1-1 and that the coi1-1 mutant was the most susceptible genotypes followed by etr2-1 genotypes. The RT-PCR revealed that PDF1.2, CHI/PR3, and ERF1, three important JA-ET responsive genes and NPR1 and PR1, which are regulated by SA signaling, were expressed upon F. poae inoculation. Our results suggest that JA and ET could play a key role in Arabidopsis leaves defense against F. poae representing the first evaluation of the response of the main A. thaliana phytohormones involved in plant defense in the presence of F. poae.

Jasmonic Acid and Ethylene Signaling Pathways Regulate Glucosinolate Levels in Plants During Rhizobacteria-Induced Systemic Resistance Against a Leaf-Chewing Herbivore.

Beneficial soil microbes can promote plant growth and induce systemic resistance (ISR) in aboveground tissues against pathogens and herbivorous insects. Despite the increasing interest in microbial-ISR against herbivores, the underlying molecular and chemical mechanisms of this phenomenon remain elusive. Using Arabidopsis thaliana and the rhizobacterium Pseudomonas simiae WCS417r (formerly known as P. fluorescens WCS417r), we here evaluate the role of the JA-regulated MYC2-branch and the JA/ET-regulated ORA59-branch in modulating rhizobacteria-ISR to Mamestra brassicae by combining gene transcriptional, phytochemical, and herbivore performance assays. Our data show a consistent negative effect of rhizobacteria-mediated ISR on the performance of M. brassicae. Functional JA- and ET-signaling pathways are required for this effect, as shown by investigating the knock-out mutants dde2-2 and ein2-1. Additionally, whereas herbivory mainly induces the MYC2-branch, rhizobacterial colonization alone or in combination with herbivore infestation induces the ORA59-branch of the JA signaling pathway. Rhizobacterial colonization enhances the synthesis of camalexin and aliphatic glucosinolates (GLS) compared to the control, while it suppresses the herbivore-induced levels of indole GLS. These changes are associated with modulation of the JA-/ET-signaling pathways. Our data show that the colonization of plant roots by rhizobacteria modulates plant-insect interactions by prioritizing the JA/ET-regulated ORA59-branch over the JA-regulated MYC2-branch. This study elucidates how microbial plant symbionts can modulate the plant immune system to mount an effective defense response against herbivorous plant attackers.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-016-0787-7) contains supplementary material, which is available to authorized users.

Transcriptome analysis of root response to citrus blight based on the newly assembled Swingle citrumelo draft genome.

BackgroundCitrus blight is a citrus tree overall decline disease and causes serious losses in the citrus industry worldwide. Although it was described more than one hundred years ago, its causal agent remains unknown and its pathophysiology is not well determined, which hampers our understanding of the disease and design of suitable disease management.ResultsIn this study, we sequenced and assembled the draft genome for Swingle citrumelo, one important citrus rootstock. The draft genome is approximately 280 Mb, which covers 74 % of the estimated Swingle citrumelo genome and the average coverage is around 15X. The draft genome of Swingle citrumelo enabled us to conduct transcriptome analysis of roots of blight and healthy Swingle citrumelo using RNA-seq. The RNA-seq was reliable as evidenced by the high consistence of RNA-seq analysis and quantitative reverse transcription PCR results (R2 = 0.966). Comparison of the gene expression profiles between blight and healthy root samples revealed the molecular mechanism underneath the characteristic blight phenotypes including decline, starch accumulation, and drought stress. The JA and ET biosynthesis and signaling pathways showed decreased transcript abundance, whereas SA-mediated defense-related genes showed increased transcript abundance in blight trees, suggesting unclassified biotrophic pathogen was involved in this disease.ConclusionsOverall, the Swingle citrumelo draft genome generated in this study will advance our understanding of plant biology and contribute to the citrus breeding. Transcriptome analysis of blight and healthy trees deepened our understanding of the pathophysiology of citrus blight.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2779-y) contains supplementary material, which is available to authorized users.

Ethylene Contributes to maize insect resistance1-Mediated Maize Defense against the Phloem Sap-Sucking Corn Leaf Aphid.

Signaling networks among multiple phytohormones fine-tune plant defense responses to insect herbivore attack. Previously, it was reported that the synergistic combination of ethylene (ET) and jasmonic acid (JA) was required for accumulation of the maize insect resistance1 (mir1) gene product, a cysteine (Cys) proteinase that is a key defensive protein against chewing insect pests in maize (Zea mays). However, this study suggests that mir1-mediated resistance to corn leaf aphid (CLA; Rhopalosiphum maidis), a phloem sap-sucking insect pest, is independent of JA but regulated by the ET-signaling pathway. Feeding by CLA triggers the rapid accumulation of mir1 transcripts in the resistant maize genotype, Mp708. Furthermore, Mp708 provided elevated levels of antibiosis (limits aphid population)- and antixenosis (deters aphid settling)-mediated resistance to CLA compared with B73 and Tx601 maize susceptible inbred lines. Synthetic diet aphid feeding trial bioassays with recombinant Mir1-Cys Protease demonstrates that Mir1-Cys Protease provides direct toxicity to CLA. Furthermore, foliar feeding by CLA rapidly sends defensive signal(s) to the roots that trigger belowground accumulation of the mir1, signifying a potential role of long-distance signaling in maize defense against the phloem-feeding insects. Collectively, our data indicate that ET-regulated mir1 transcript accumulation, uncoupled from JA, contributed to heightened resistance to CLA in maize. In addition, our results underscore the significance of ET acting as a central node in regulating mir1 expression to different feeding guilds of insect herbivores.

Systemic Resistance Induced by Volatile Organic Compounds Emitted by Plant Growth-Promoting Fungi in Arabidopsis thaliana

Volatile organic compounds (VOC) were extracted and identified from plant growth-promoting fungi (PGPF), Phoma sp., Cladosporium sp. and Ampelomyces sp., using gas chromatography–mass spectrometry (GC-MS). Among the three VOC extracted, two VOC blends (emitted from Ampelomyces sp. and Cladosporium sp.) significantly reduced disease severity in Arabidopsis plants against Pseudomonas syringae pv. tomato DC3000 (Pst). Subsequently, m-cresol and methyl benzoate (MeBA) were identified as major active volatile compounds from Ampelomyces sp. and Cladosporium sp., respectively, and found to elicit induced systemic resistance (ISR) against the pathogen. Molecular signaling for disease suppression by the VOC were investigated by treating different mutants and transgenic Arabidopsis plants impaired in salicylic acid (SA) or Jasmonic acid (JA)/ethylene (ET) signaling pathways with m-cresol and MeBA followed by challenge inoculation with Pst. Results show that the level of protection was significantly lower when JA/ET-impaired mutants were treated with MeBA, and in SA-, and JA/ET-disrupted mutants after m-cresol treatment, indicating the involvement of these signal transduction pathways in the ISR primed by the volatiles. Analysis of defense-related genes by real-time qRT-PCR showed that both the SA-and JA-signaling pathways combine in the m-cresol signaling of ISR, whereas MeBA is mainly involved in the JA-signaling pathway with partial recruitment of SA-signals. The ET-signaling pathway was not employed in ISR by the volatiles. Therefore, this study identified two novel volatile components capable of eliciting ISR that may be promising candidates in biological control strategy to protect plants from diseases.

Ethylene Signaling Pathway Modulates Attractiveness of Host Roots to the Root-Knot Nematode Meloidogyne hapla

Infective juveniles of the root-knot nematode Meloidogyne hapla are attracted to the zone of elongation of roots where they invade the host but little is known about what directs the nematode to this region of the root. We found that Arabidopsis roots exposed to an ethylene (ET)-synthesis inhibitor attracted significantly more nematodes than control roots and that ET-overproducing mutants were less attractive. Arabidopsis seedlings with ET-insensitive mutations were generally more attractive whereas mutations resulting in constitutive signaling were less attractive. Roots of the ET-insensitive tomato mutant Never ripe (Nr) were also more attractive, indicating that ET signaling also modulated attraction of root-knot nematodes to this host. ET-insensitive mutants have longer roots due to reduced basipetal auxin transport. However, assessments of Arabidopsis mutants that differ in various aspects of the ET response suggest that components of the ET-signaling pathway directly affecting root length are not responsible for modulating root attractiveness and that other components of downstream signaling result in changes in levels of attractants or repellents for M. hapla. These signals may aid in directing this pathogen to an appropriate host and invasion site for completing its life cycle.

Proteomic responses in Arabidopsis thaliana seedlings treated with ethylene

Ethylene (ET) is a volatile hormone that modulates fruit ripening, plant growth, development and stress responses. Key components of the ET-signaling pathway identified by genetic dissection in Arabidopsis thaliana include five ET receptors, the negative regulator CTR1 and the positive regulator EIN2, all of which localize to the endoplasmic reticulum. Mechanisms of signaling among these proteins are still unresolved and targets of ET responses are not fully known. So, we used mass spectrometry to identify proteins in microsomal membrane preparations from etiolated A. thaliana seedlings maintained in ambient air or treated with ET for 3 h. We compared 3814 proteins from ET-exposed seedlings and controls and identified 304 proteins with significant accumulation changes. The proteins with increased accumulation were involved in ET biosynthesis, cell morphogenesis, oxidative stress and vesicle secretion while those with decreased accumulation were ribosomal proteins and proteins positively regulated by brassinosteroid, another hormone involved in cell elongation. Several proteins, including EIN2, appeared to be differentially phosphorylated upon ET treatment, which suggests that the activity or stability of these proteins may be controlled by phosphorylation. TUA3, a component of microtubules that contributes to cellular morphological change, exhibited both increased accumulation and differential phosphorylation upon ET treatment. To verify the role of TUA3 in the ET response, tua3 mutants were evaluated. Mutant seedlings had altered ET-associated growth movements. The data indicate that ET perception leads to rapid proteomic change and that these changes are an important part of signaling and development. The data serve as a foundation for exploring ET signaling through systems biology.