Expression profile of jasmonic acid-induced genes and the induced resistance against the root-knot nematode (Meloidogyne incognita) in tomato plants (Solanum lycopersicum) after foliar treatment with methyl jasmonate

Defence and nutrition synergistically contribute to the distinct tolerance of rice subspecies to the stem borer, Chilo suppressalis

Damage caused by the rice striped stem borer (SSB), Chilo suppressalis (Walker) (Lepidoptera: Pyralidae), is much more severe on indica/xian rice than on japonica/geng rice (Oryza sativa) which matches pest outbreak data in cropping regions of China. The mechanistic basis of this difference among rice subspecies remains unclear. Using transcriptomic, metabolomic and genetic analyses in combination with insect bioassay experiments, we showed that japonica and indica rice utilise different defence responses to repel SSB, and that SSB exploited plant nutrition deficiencies in different ways in the subspecies. The more resistant japonica rice induced patterns of accumulation of methyl jasmonate (MeJA-part of a defensive pathway) and vitamin B1 (VB1 -a nutrition pathway) distinct from indica cultivars. Using gene-edited rice plants and SSB bioassays, we found that MeJA and VB1 jointly affected the performance of SSB by disrupting juvenile hormone levels. In addition, genetic variants of key biosynthesis genes in the MeJA and VB1 pathways (OsJMT and OsTH1, respectively) differed between japonica and indica rice and contributed to performance differences; in indica rice, SSB avoided the MeJA defence pathway and hijacked the VB1 nutrition-related pathway to promote development. The findings highlight important genetic and mechanistic differences between rice subspecies affecting SSB damage which could be exploited in plant breeding for resistance.

Unveiling the Diversity: Plant Parasitic Nematode Effectors and Their Plant Interaction Partners

Root-knot and cyst nematodes are two groups of plant parasitic nematodes that cause the majority of crop losses in agriculture. As a result, these nematodes are the focus of most nematode effector research. Root-knot and cyst nematode effectors are defined as secreted molecules, typically proteins, with crucial roles in nematode parasitism. There are likely hundreds of secreted effector molecules exuded through the nematode stylet into the plant. The current research has shown that nematode effectors can target a variety of host proteins and have impacts that include the suppression of plant immune responses and the manipulation of host hormone signaling. The discovery of effectors that localize to the nucleus indicates that the nematodes can directly modulate host gene expression for cellular reprogramming during feeding site formation. In addition, plant peptide mimicry by some nematode effectors highlights the sophisticated strategies the nematodes employ to manipulate host processes. Here we describe research on the interactions between nematode effectors and host proteins that will provide insights into the molecular mechanisms underpinning plant-nematode interactions. By identifying the host proteins and pathways that are targeted by root-knot and cyst nematode effectors, scientists can gain a better understanding of how nematodes establish feeding sites and subvert plant immune responses. Such information will be invaluable for future engineering of nematode-resistant crops, ultimately fostering advancements in agricultural practices and crop protection. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Autophagy promotes jasmonate-mediated defense against nematodes

Autophagy, as an intracellular degradation system, plays a critical role in plant immunity. However, the involvement of autophagy in the plant immune system and its function in plant nematode resistance are largely unknown. Here, we show that root-knot nematode (RKN; Meloidogyne incognita) infection induces autophagy in tomato (Solanum lycopersicum) and different atg mutants exhibit high sensitivity to RKNs. The jasmonate (JA) signaling negative regulators JASMONATE-ASSOCIATED MYC2-LIKE 1 (JAM1), JAM2 and JAM3 interact with ATG8s via an ATG8-interacting motif (AIM), and JAM1 is degraded by autophagy during RKN infection. JAM1 impairs the formation of a transcriptional activation complex between ETHYLENE RESPONSE FACTOR 1 (ERF1) and MEDIATOR 25 (MED25) and interferes with transcriptional regulation of JA-mediated defense-related genes by ERF1. Furthermore, ERF1 acts in a positive feedback loop and regulates autophagy activity by transcriptionally activating ATG expression in response to RKN infection. Therefore, autophagy promotes JA-mediated defense against RKNs via forming a positive feedback circuit in the degradation of JAMs and transcriptional activation by ERF1.

Tomato defence against Meloidogyne incognita by jasmonic acid-mediated fine-tuning of kaempferol homeostasis

Jasmonic acid (JA) is involved in the modulation of defence and growth activities in plants. The best-characterized growth-defence trade-offs stem from antagonistic crosstalk among hormones. In this study, we first confirmed that JA negatively regulates root-knot nematode (RKN) susceptibility via the root exudates (REs) of tomato plants. Omics and toxicological analyses implied that kaempferol, a type of flavonol, from REs has a negative effect on RKN infection. We demonstrated that SlMYB57 negatively regulated kaempferol contents in tomato roots, whereas SlMYB108/112 had the opposite effect. We revealed that JA fine-tuned the homeostasis of kaempferol via SlMYB-mediated transcriptional regulation and the interaction between SlJAZs and SlMYBs, thus ensuring a balance between lateral root (LR) development and RKN susceptibility. Overall, this work provides novel insights into JA-modulated LR development and RKN susceptibility mechanisms and elucidates a trade-off model mediated by JA in plants encountering stress.

Evaluation of the mechanism of action of Bacillus spp. to manage Meloidogyne incognita with split root assay, RT-qPCR and qPCR

The goal of this research is to determine the mechanism of action of two Bacillus spp. that can manage Meloidogyne incognita population density in cotton. The overall objectives are 1) determine the efficacy and direct antagonistic capabilities of the Bacillus spp. and 2) determine the systemic capabilities of the Bacillus spp. The greenhouse in planta assay indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could manage M. incognita similarly to the chemical standard fluopyram. An in vitro assay determined that B. firmus I-1582 and its extracted metabolites were able to directly manage M. incognita second stage juveniles by increasing mortality rate above 75%. A split root assay, used to determine systemic capabilities of the bacteria, indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could indirectly decrease the nematode population density. Another species, B. mojavensis strain 2, also demonstrated systemic capabilities but was not a successful biological control agent because it supported a high population density in greenhouse in planta assay and in the split root assay. A RT-qPCR assay was used to confirm any systemic activity observed in the split root assay. At 24 hours both B. amyloliquefaciens QST713 and B. firmus I-1582 upregulated one gene involved in the initial stages of JA synthesis pathway but not another gene involved in the later stages of JA synthesis. These results point to a JA intermediate molecule, most likely OPDA, stimulated by the bacteria rather than JA in a short-term systemic response. After 1 week, the Bacillus spp. stimulated a SA-responsive defense related gene. The long-term systemic response to the Bacillus spp. indicates salicylic acid also plays a role in defense conferred by these bacteria. The final assay was a qPCR to determine the concentration of the bacteria on the cotton roots after 24 days. Bacillus amyloliquefaciens QST713 and B. firmus I-43 1582 were able to colonize the root successfully, with the concentration after 24 days not significantly differing from the concentration at inoculation. This study identifies two bacteria that work via systemic resistance and will help aid in implementing these species in an integrated management system.

Rooting Out the Mechanisms of Root-Knot Nematode-Plant Interactions

Root-knot nematodes (RKNs; Meloidogyne spp.) engage in complex parasitic interactions with many different host plants around the world, initiating elaborate feeding sites and disrupting host root architecture. Although RKNs have been the focus of research for many decades, new molecular tools have provided useful insights into the biological mechanisms these pests use to infect and manipulate their hosts. From identifying host defense mechanisms underlying resistance to RKNs to characterizing nematode effectors that alter host cellular functions, the past decade of research has significantly expanded our understanding of RKN-plant interactions, and the increasing number of quality parasite and host genomes promises to enhance future research efforts into RKNs. In this review, we have highlighted recent discoveries, summarized the current understanding within the field, and provided links to new and useful resources for researchers. Our goal is to offer insights and tools to support the study of molecular RKN-plant interactions.

Arabidopsis thaliana AtHRS1 gene is involved in the response to Heterodera schachtii infection and its overexpression hampers development of syncytia and involves a jasmonic acid-dependent mechanism

Sedentary plant parasitic nematodes have developed competences to reprogram host plant cell metabolism via sophisticated manipulation of gene expression, leading to the formation of permanent feeding sites for an unlimited source of food. Arabidopsis thaliana and the beet cyst nematode Heterodera schachtii is a good model for studying the mechanisms of compatible plant-nematode interactions and basic plant responses to nematode infection. Transcription factors are proteins that modulate plant reactions during regular development and under different biotic and abiotic stresses via direct binding to promoter regions of genes. Here, we report on the AtHRS1 gene encoding a MYB-related transcription factor belonging to the GARP family, whose expression is downregulated in syncytia, as confirmed by gene expression analysis. Constitutive overexpression of AtHRS1 disturbed the development of nematode-induced syncytia and led to a reduction in the number of developed females in transgenic A. thaliana roots. In contrast, the hrs1 mutant with decreased expression of AtHRS1 was more susceptible to cyst nematode infection. The influence of AtHRS1 on selected elements of the JA-dependent defence pathway suggests its mode of action in plant response to nematode attack. Based on these results, we suggest that the downregulation of AtHRS1 expression by nematode is important for its successful development.

RNA-Seq of Cyst Nematode Infestation of Potato (Solanum tuberosum L.): A Comparative Transcriptome Analysis of Resistant and Susceptible Cultivars

Potato (Solanum tuberosum L.) is an important food crop worldwide, and potato cyst nematodes (PCNs) are among the most serious pests. The identification of disease resistance genes and molecular markers for PCN infestation can aid in crop improvement research programs against PCN infestation. In the present study, we used high-throughput RNA sequencing to investigate the comprehensive resistance mechanisms induced by PCN infestation in the resistant cultivar Kufri Swarna and the susceptible cultivar Kufri Jyoti. PCN infestation induced 791 differentially expressed genes in resistant cultivar Kufri Swarna, comprising 438 upregulated and 353 downregulated genes. In susceptible cultivar Kufri Jyoti, 2225 differentially expressed genes were induced, comprising 1247 upregulated and 978 downregulated genes. We identified several disease resistance genes (KIN) and transcription factors (WRKY, HMG, and MYB) that were upregulated in resistant Kufri Swarna. The differentially expressed genes from several enriched KEGG pathways, including MAPK signaling, contributed to the disease resistance in Kufri Swarna. Functional network analysis showed that several cell wall biogenesis genes were induced in Kufri Swarna in response to infestation. This is the first study to identify underlying resistance mechanisms against PCN and host interaction in Indian potato varieties.

Quantitative detection of induced systemic resistance genes of potato roots upon ethylene treatment and cyst nematode, Globodera rostochiensis, infection during plant–nematode interactions

Potato cyst nematodes caused by Globodera rostochiensis, are quarantine-restricted pests causing significant yield losses to potato growers. The phytohormone ethylene play significant roles in various plant-pathogen interactions, however, the molecular knowledge of how ethylene influences potato–nematode interaction is still lacking. Precise detection of potato-induced genes is essential for recognizing plant-induced systemic resistance (ISR). Candidate genes or PR- proteins with putative functions in modulating the response to potato cyst nematode stress were selected and functionally characterized. Using real-time polymerase chain reaction (RT-PCR), we measured the quantified expression of four pathogenesis-related (PR) genes, PR2, PR3, peroxidase, and polyphenol oxidase. The activation of these genes is intermediate during the ISR signaling in the root tissues. Using different ethylene concentrations could detect and induce defense genes in infected potato roots compared to the control treatment. The observed differences in the gene expression of treated infected plants are because of different concentrations of ethylene treatment and pathogenicity. Besides, the overexpressed or suppressed of defense- related genes during developmental stages and pathogen infection. We concluded that ethylene treatments positively affected potato defensive genes expression levels against cyst nematode infection. The results emphasize the necessity of studying molecular signaling pathways controlling biotic stress responses. Understanding such mechanisms will be critical for the development of broad-spectrum and stress-tolerant crops in the future.

Leaf herbivory counteracts nematode-triggered repression of jasmonate-related defenses in tomato roots

Shoot herbivores may influence the communities of herbivores associated with the roots via inducible defenses. However, the molecular mechanisms and hormonal signaling underpinning the systemic impact of leaf herbivory on root-induced responses against nematodes remain poorly understood. By using tomato (Solanum lycopersicum) as a model plant, we explored the impact of leaf herbivory by Manduca sexta on the performance of the root knot nematode Meloidogyne incognita. By performing glasshouse bioassays, we found that leaf herbivory reduced M. incognita performance in the roots. By analyzing the root expression profile of a set of oxylipin-related marker genes and jasmonate root content, we show that leaf herbivory systemically activates the 13-Lipoxigenase (LOX) and 9-LOX branches of the oxylipin pathway in roots and counteracts the M. incognita-triggered repression of the 13-LOX branch. By using untargeted metabolomics, we also found that leaf herbivory counteracts the M. incognita-mediated repression of putative root chemical defenses. To explore the signaling involved in this shoot-to-root interaction, we performed glasshouse bioassays with grafted plants compromised in jasmonate synthesis or perception, specifically in their shoots. We demonstrated the importance of an intact shoot jasmonate perception, whereas having an intact jasmonate biosynthesis pathway was not essential for this shoot-to-root interaction. Our results highlight the impact of leaf herbivory on the ability of M. incognita to manipulate root defenses and point to an important role for the jasmonate signaling pathway in shoot-to-root signaling.

Phytohormones selectively affect plant parasitic nematodes associated with Arabidopsis roots

Phytohormones may affect plant-nematode interactions directly as chemo-attractants or -repellents, or indirectly through the root-associated microbiome or through host defense mechanisms. However, the exact roles of phytohormones in these complex plant-soil-nematode interactions are not well understood. We used Arabidopsis thaliana mutants impaired in phytohormone synthesis or sensitivity to elucidate their role in root-nematode interactions. As root-associated microorganisms may modulate these interactions, we explored correlations between the relative abundances of root-associated nematodes, and bacteria and fungi using amplicon sequencing. We found distinct shifts in relative abundances of a range of nematode taxa in the A. thaliana phytohormone mutants. The root knot nematode Meloidogyne hapla, a sedentary endoparasitic species that is in intimate contact with the host, was highly enriched in JA-, SA- and SL-impaired lines, and in an ET-insensitive line. Positive or negative correlations between specific microbial and nematode taxa were observed, but, as the inference of causal relationships between microbiome responses and effects on nematode communities is premature, this should be studied in detail in future studies. In conclusion, genetic derailment of hormonal balances generally rendered plants vulnerable to endoparasitic nematode attack. Furthermore, preliminary data suggest that this effect may be partially modulated by the associated microbiome.

A tomato receptor-like cytoplasmic kinase, SlZRK1, acts as a negative regulator in wound-induced jasmonic acid accumulation and insect resistance

Jasmonates accumulate rapidly and act as key regulators in response to mechanical wounding, but few studies have linked receptor-like cytoplasmic kinases (RLCKs) to wound-induced jasmonic acid (JA) signaling cascades. Here, we identified a novel wounding-induced RLCK-XII-2 subfamily member (SlZRK1) in tomato (Solanum lycopersicum) that was closely related to Arabidopsis HOPZ-ETI-DEFICIENT 1 (ZED1)-related kinases 1 based on phylogenetic analysis. SlZRK1 was targeted to the plasma membrane of tobacco mesophyll protoplasts as determined by transient co-expression with the plasma membrane marker mCherry-H+-ATPase. Catalytic residue sequence analysis and an in vitro kinase assay indicated that SlZRK1 may act as a pseudokinase. To further analyse the function of SlZRK1, we developed two stable knock-out mutants by CRISPR/Cas9. Loss of SlZRK1 significantly altered the expression of genes involved in JA biosynthesis, salicylic acid biosynthesis, and ethylene response. Furthermore, after mechanical wounding treatment, slzrk1 mutants increased transcription of early wound-inducible genes involved in JA biosynthesis and signaling. In addition, JA accumulation after wounding and plant resistance to herbivorous insects also were enhanced. Our findings expand plant regulatory networks in the wound-induced JA production by adding RLCKs as a new component in the wound signal transduction pathway.

The Meloidogyne javanica effector Mj2G02 interferes with jasmonic acid signalling to suppress cell death and promote parasitism in Arabidopsis

Plant-parasitic nematodes can cause devastating damage to crops. These nematodes secrete effectors that suppress the host immune responses to enhance their survival. In this study, Mj2G02, an effector from Meloidogyne javanica, is described. In situ hybridization and transcriptional analysis showed that Mj2G02 was highly expressed in the early infection stages and exclusively expressed in the nematode subventral oesophageal gland cells. In planta RNA interference targeting Mj2G02 impaired M. javanica parasitism, and Mj2G02-transgenic Arabidopsis lines displayed more susceptibility to M. javanica. Using an Agrobacterium-mediated transient expression system and plant immune response assays, we demonstrated that Mj2G02 localized in the plant cell nuclei and could suppress Gpa2/RBP-1-induced cell death. Moreover, by RNA-Seq and quantitative reverse transcription PCR analyses, we showed that Mj2G02 was capable of interfering with the host jasmonic acid (JA) signalling pathway. Multiple jasmonate ZIM-domain (JAZ) genes were significantly upregulated, whereas the JAR1 gene and four JA-responsive genes, MYC3, UPI, THI2.1, and WRKY75, were significantly downregulated. In addition, HPLC analysis showed that the endogenous jasmonoyl-isoleucine (JA-Ile) level in Mj2G02-transgenic Arabidopsis lines was significantly decreased compared to that in wildtype plants. Our results indicate that the M. javanica effector Mj2G02 suppresses the plant immune response, therefore facilitating nematode parasitism. This process is probably mediated by a JA-Ile reduction and JAZ enhancement to repress JA-responsive genes.

Role of jasmonic acid in plants: the molecular point of view

Recent updates in JA biosynthesis, signaling pathways and the crosstalk between JA and others phytohormones in relation with plant responses to different stresses. In plants, the roles of phytohormone jasmonic acid (JA), amino acid conjugate (e.g., JA-Ile) and their derivative emerged in last decades as crucial signaling compounds implicated in stress defense and development in plants. JA has raised a great interest, and the number of researches on JA has increased rapidly highlighting the importance of this phytohormone in plant life. First, JA was considered as a stress hormone implicated in plant response to biotic stress (pathogens and herbivores) which confers resistance to biotrophic and hemibiotrophic pathogens contrarily to salicylic acid (SA) which is implicated in plant response to necrotrophic pathogens. JA is also implicated in plant responses to abiotic stress (such as soil salinity, wounding and UV). Moreover, some researchers have recently revealed that JA controls several physiological processes like root growth, growth of reproductive organs and, finally, plant senescence. JA is also involved in the biosynthesis of various metabolites (e.g., phytoalexins and terpenoids). In plants, JA signaling pathways are well studied in few plants essentially Arabidopsis thaliana, Nicotiana benthamiana, and Oryza sativa L. confirming the crucial role of this hormone in plants. In this review, we highlight the last foundlings about JA biosynthesis, JA signaling pathways and its implication in plant maturation and response to environmental constraints.

Phytol, a Constituent of Chlorophyll, Induces Root-Knot Nematode Resistance in Arabidopsis via the Ethylene Signaling Pathway

Root-knot nematodes (RKNs; Meloidogyne spp.) parasitize the roots or stems of a wide range of plant species, resulting in severe damage to the parasitized plant. The phytohormone ethylene (ET) plays an important role in signal transduction pathways leading to resistance against RKNs. However, little is currently known about the induction mechanisms of ET-dependent RKN resistance. Inoculation of Arabidopsis thaliana roots with RKNs decreased chlorophyll contents in aerial parts of the plant. We observed accumulation of phytol, a constituent of chlorophyll and a precursor of tocopherols, in RKN-parasitized roots. Application of sclareol, a diterpene that has been shown to induce ET-dependent RKN resistance, to the roots of Arabidopsis plants increased phytol contents in roots accompanied by a decrease in chlorophyll in aerial parts. Exogenously applied phytol inhibited RKN penetration of roots without exhibiting nematicidal activity. This phytol-induced inhibition of RKN penetration was attenuated in the ET-insensitive Arabidopsis mutant ein2-1. Exogenously applied phytol enhanced the production of α-tocopherol and expression of VTE5, a gene involved in tocopherol production, in Arabidopsis roots. α-Tocopherol exerted induction of RKN resistance similar to that of phytol and showed increased accumulation in roots inoculated with RKNs. Furthermore, the Arabidopsis vte5 mutant displayed no inhibition of RKN penetration in response to phytol. These results suggest that exogenously applied phytol induces EIN2-dependent RKN resistance, possibly via tocopherol production.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Gene Expression of Protease Inhibitors in Tomato Plants with Invasion by Root-Knot Nematode Meloidogyne incognita and Modulation of Their Activity with Salicylic and Jasmonic Acids

Abstract—

The expression of the genes encoding the inhibitors of serine (ISP) and cysteine ​​proteinases (ICP) was studied in the roots of tomato plants resistant and susceptible to the root-knot nematode Meloidogyne incognita during infection and under the effects of signaling molecules: salicylic (SA) and jasmonic (JA) acids. It was shown that, upon infection, resistant plants are characterized by an increased accumulation of transcripts of the ICP and ISP genes at the stages of penetration and development in the roots, while the level of transcription does not change in susceptible plants. There was a significant decrease in nematode invasion in susceptible plants after treatment with SA or JA compared to untreated plants, which makes it possible to determine the role of the studied proteinase inhibitors in resistance induced by signaling molecules. It was revealed that an increase in expression of the genes of proteinase inhibitors is accompanied by inhibition of the reproductive potential and size of M. incognita females, as well as by a decrease in plant infection.

Current Utility of Plant Growth-Promoting Rhizobacteria as Biological Control Agents towards Plant-Parasitic Nematodes

Plant-parasitic nematodes (PPN) are among the most economically and ecologically damaging pests, causing severe losses of crop production worldwide. Chemical-based nematicides have been widely used, but these may have adverse effects on human health and the environment. Hence, biological control agents (BCAs) have become an alternative option for controlling PPN, since they are environmentally friendly and cost effective. Lately, a major effort has been made to evaluate the potential of a commercial grade strain of plant growth-promoting rhizobacteria (PGPR) as BCAs, because emerging evidence has shown that PGPR can reduce PPN in infested plants through direct and/or indirect antagonistic mechanisms. Direct antagonism occurs by predation, release of antinematicidal metabolites and semiochemicals, competition for nutrients, and niche exclusion. However, the results of direct antagonism may be inconsistent due to unknown endogenous and exogenous factors that may prevent PGPR from colonizing plant's roots. On the other hand, indirect antagonism may occur from the induced systemic resistance (ISR) that primes whole plants to better fight against various biotic and abiotic constraints, actuating faster and/or stronger defense responses (adaption), enhancing their promise as BCAs. Hence, this review will briefly revisit (i) two modes of PGPR in managing PPN, and (ii) the current working models and many benefits of ISR, in the aim of reassessing current progresses and future directions for isolating more effective BCAs and/or developing better PPN management strategy.

Initial responses of the trap-crop, Solanum sisymbriifolium, to Globodera pallida invasions

Many researchers today are looking for mechanisms underlying plant defenses against nematodes by identifying differentially expressed genes in domesticated hosts. In order to provide a different perspective, we analyzed the root transcriptome of an undomesticated non-host species, Solanum sisymbriifolium Lamark (SSI) before and after Globodera pallida infection. Utilizing RNAseq analyses, we identified changes in the expression of 277 transcripts. Many of these genes were not annotated; however, the annotated set included peroxidases, reactive oxygen species-producing proteins, and regulators of cell death. Importantly, 60% of the nematode-responsive genes did not respond to physical damage to root tissues, or to exogenous treatments with either salicylic acid or methyl jasmonate. Based on this, we speculate that the majority of changes in SSI gene expression were promoted by either nematode effectors, pathogen-associated molecular patterns (PAMPs), or by exposure to untested endogenous signaling molecules such as ethylene, or by exposure to multiple stimuli. This study incorporates our findings into a model that accounts for part of this plant's unusual resistance to nematodes.

Profiling of defense responsive pathway regulatory genes in Asian rice (Oryza sativa) against infection of Meloidogyne graminicola (Nematoda:Meloidogynidae)

In the present study, 36 Asian rice cultivars/landraces were evaluated against M. graminicola under in vitro conditions using soilless Pluronic gel medium. The cultivars/genotypes Phule Radha, EK 70, LK 248 and Khalibagh showed significantly reduced nematode infection, endoparasitic development, and derived multiplication factor indicating the presence of resistance, while Halvi Sal 17 was found to be most susceptible. Performance of selected genotypes showing resistance/susceptibility under in vitro conditions was further confirmed in soil which also revealed Phule Radha to be highly resistant and Halvi Sal 17 as the most susceptible genotype. Further, expression profile of plant defense responsive genes related to MAPK pathway, phytohormones, PR-proteins and callose and lignin synthesis were quantified in Phule Radha (the most resistant) and Halvi Sal 17 (the most susceptible) at 2 and 6 days post nematode inoculation. Significant upregulated expression of several defensive genes was observed in the resistant cultivar Phule Radha in contrast to insignificant expression in the susceptible varieties. The resistant genotype identified in the present study will be highly promising for resistance breeding in rice against M. graminicola.

Bacillus firmus Strain I-1582, a Nematode Antagonist by Itself and Through the Plant

Bacillus firmus I-1582 is approved in Europe for the management of Meloidogyne on vegetable crops. However, little information about its modes of action and temperature requirements is available, despite the effect of these parameters in its efficacy. The cardinal temperatures for bacterial growth and biofilm formation were determined. The bacteria was transformed with GFP to study its effect on nematode eggs and root colonization of tomato (Solanum lycopersicum) and cucumber (Cucumis sativus) by laser-scanning confocal microscopy. Induction of plant resistance was determined in split-root experiments and the dynamic regulation of genes related to jasmonic acid (JA) and salicylic acid (SA) by RT-qPCR at three different times after nematode inoculation. The bacteria was able to grow and form biofilms between 15 and 45°C; it degraded egg-shells and colonized eggs; it colonized tomato roots more extensively than cucumber roots; it induced systemic resistance in tomato, but not in cucumber; SA and JA related genes were primed at different times after nematode inoculation in tomato, but only the SA-related gene was up-regulated at 7 days after nematode inoculation in cucumber. In conclusion, B. firmus I-1582 is active at a wide range of temperatures; its optimal growth temperature is 35°C; it is able to degrade Meloidogyne eggs, and to colonize plant roots, inducing systemic resistance in a plant dependent species manner.

Pochonia chlamydosporia Induces Plant-Dependent Systemic Resistance to Meloidogyne incognita

Meloidogyne spp. are the most damaging plant parasitic nematodes for horticultural crops worldwide. Pochonia chlamydosporia is a fungal egg parasite of root-knot and cyst nematodes able to colonize the roots of several plant species and shown to induce plant defense mechanisms in fungal-plant interaction studies, and local resistance in fungal-nematode-plant interactions. This work demonstrates the differential ability of two out of five P. chlamydosporia isolates, M10.43.21 and M10.55.6, to induce systemic resistance against M. incognita in tomato but not in cucumber in split-root experiments. The M10.43.21 isolate reduced infection (32-43%), reproduction (44-59%), and female fecundity (14.7-27.6%), while the isolate M10.55.6 only reduced consistently nematode reproduction (35-47.5%) in the two experiments carried out. The isolate M10.43.21 induced the expression of the salicylic acid pathway (PR-1 gene) in tomato roots 7 days after being inoculated with the fungal isolate and just after nematode inoculation, and at 7 and 42 days after nematode inoculation too. The jasmonate signaling pathway (Lox D gene) was also upregulated at 7 days after nematode inoculation. Thus, some isolates of P. chlamydosporia can induce systemic resistance against root-knot nematodes but this is plant species dependent.

Ozone treatments activate defence responses against Meloidogyne incognita and Tomato spotted wilt virus in tomato

BACKGROUND

Ozonated water (O₃ wat) soil drench and/or foliar spray applications were evaluated for their potential to control the root-knot nematode Meloidogyne incognita (RKN) and the airborne pathogen Tomato spotted wilt virus (TSWV) in tomato. We investigated how O₃ wat modulates the salicylic acid/jasmonic acid/ethylene (SA/JA/ET) signalling network in the host, locally and systemically, to induce resistance to nematode and virus.

RESULTS

The application as soil drench was effective in reducing the number of galls and egg masses, but did not reduce the incidence and severity of TSWV infection. Conversely, O₃ wat applied by foliar spray decreased TSWV disease incidence and severity (-20%), but was not able to control M. incognita infection. SA-related genes were generally upregulated in both locally treated and systemically reached tissues, showing a positive action of the O₃ wat treatment on SA signalling. Neither O₃ wat application method significantly altered JA-related gene expression in either direction. ET-related genes were differentially regulated by root or leaf treatments, indicating that O₃ wat may have different effects on ET-mediated signalling in different organs. JA/ET/SA related pathways were differentially modulated by O₃ wat in the presence of either RKN or TSWV.

CONCLUSION

O₃ wat had a higher efficacy when applied directly to organs challenged by the pathogens, although it was potentially able to stimulate defence responses through the activation of SA signalling. Owing to its safety and effectiveness in controlling nematode and virus infections, O₃ wat can be considered as a possible alternative tool for sustainable disease management practices. © 2019 Society of Chemical Industry.

Effective approaches to study the plant-root knot nematode interaction

Plant-parasitic nematodes cause major agricultural losses worldwide. Examining the molecular mechanisms underlying plant-nematode interactions and how plants respond to different invading pathogens is attracting major attention to reduce the expanding gap between agricultural production and the needs of the growing world population. This review summarizes the most recent developments in plant-nematode interactions and the diverse approaches used to improve plant resistance against root knot nematode (RKN). We will emphasize the recent rapid advances in genome sequencing technologies, small interfering RNA techniques (RNAi) and targeted genome editing which are contributing to the significant progress in understanding the plant-nematode interaction mechanisms. Also, molecular approaches to improve plant resistance against nematodes are considered.

Strigolactones positively regulate defense against root-knot nematodes in tomato

Strigolactones (SLs) are carotenoid-derived phytohormones that are known to influence various aspects of plant growth and development. As root-derived signals, SLs can enhance symbiosis between plants and arbuscular mycorrhizal fungi (AMF). However, little is known about the roles of SLs in plant defense against soil-borne pathogens. Here, we determined that infection with root-knot nematodes (RKNs; Meloidogyne incognita) induced SL biosynthesis in roots of tomato (Solanum lycopersicum). Silencing of SL biosynthesis genes compromised plant defense against RKNs, whilst application of the SL analog racGR24 enhanced it. Accumulation of endogenous jasmonic acid (JA) and abscisic acid (ABA) in the roots in response to RKN infection was enhanced by silencing of SL biosynthetic genes and was suppressed by application of racGR24. Genetic evidence showed that JA was a positive regulator of defense against RKNs while ABA was a negative regulator. In addition, racGR24 enhanced the defense against nematode in a JA-deficient mutant but not in an ABA-deficient mutant. Silencing of SL biosynthetic genes resulted in up-regulation of MYC2, which negatively regulated defense against RKNs. Our results demonstrate that SLs play a positive role in nematode defense in tomato and that MYC2 negatively regulates this defense, potentially by mediating hormone crosstalk among SLs, ABA and JA.

Jasmonic acid modulates Meloidogyne incognita – tomato plant interactions

Molecular aspects of the responses of tomato (Solanum lycopersicum) plants to invasion by Meloidogyne incognita, as well as the nematode reproduction capacity, were investigated and the role of jasmonic acid (JA) in these interactions was evaluated. Real-time quantitative PCR analysis showed that resistant and susceptible plants had similar levels of Mi1.2, PR1 and PR6 gene expression in stress-free conditions. During nematode invasion resistant plants showed up-regulation of Mi1.2, PR1 and PR6 genes and no reproduction of M. incognita. By contrast, susceptible plants showed no response in gene expression and the nematode had a high level of reproduction. Treatment of tomato plants with JA modulated Mi1.2 and PR6 gene expression that was accompanied by a suppression of the M. incognita reproduction on the roots of JA-treated susceptible plants.

Impacts of Root Metabolites on Soil Nematodes

Plant parasitic nematodes cause significant crop damage globally. Currently, many nematicides have been banned or are being phased out in Europe and other parts of the world because of environmental and human health concerns. Therefore, we need to focus on sustainable and alternative methods of nematode control to protect crops. Plant roots contain and release a wide range of bioactive secondary metabolites, many of which are known defense compounds. Hence, profound understanding of the root mediated interactions between plants and plant parasitic nematodes may contribute to efficient control and management of pest nematodes. In this review, we have compiled literature that documents effects of root metabolites on plant parasitic nematodes. These chemical compounds act as either nematode attractants, repellents, hatching stimulants or inhibitors. We have summarized the few studies that describe how root metabolites regulate the expression of nematode genes. As non-herbivorous nematodes contribute to decomposition, nutrient mineralization, microbial community structuring and control of herbivorous insect larvae, we also review the impact of plant metabolites on these non-target organisms.

COP9 Signalosome CSN4 and CSN5 Subunits Are Involved in Jasmonate-Dependent Defense Against Root-Knot Nematode in Tomato

COP9 signalosome (CSN) is an evolutionarily conserved regulatory component of the ubiquitin/proteasome system that plays crucial roles in plant growth and stress tolerance; however, the mechanism of COP9-mediated resistance to root-knot nematodes (RKNs, e.g. Meloidogyne incognita) is not fully understood in plants. In the present study, we found that RKN infection in the roots rapidly increases the transcript levels of CSN subunits 4 and 5 (CSN4 and CSN5) and their protein accumulation in tomato (Solanum lycopersicum) plants. Suppression of CSN4 or CSN5 expression resulted in significantly increased number of egg masses and aggravated RKN-induced lipid peroxidation of cellular membrane but inhibited RKN-induced accumulation of CSN4 or CSN5 protein in tomato roots. Importantly, the RKN-induced accumulation of jasmonic acid (JA) and JA-isoleucine (JA-Ile), as well as the transcript levels of JA-related biosynthetic and signaling genes were compromised by CSN4 or CSN5 gene silencing. Moreover, protein-protein interaction assays demonstrated that CSN4 and CSN5B interact with the jasmonate ZIM domain 2 (JAZ2), which is the signaling component of the JA pathway. Silencing of CSN4 or CSN5 also compromises RKN-induced JAZ2 expression. Together, our findings indicate that CSN4 and CSN5 play critical roles in JA-dependent basal defense against RKN.

A Meloidogyne incognita effector MiISE5 suppresses programmed cell death to promote parasitism in host plant

Root-knot nematodes (RKNs) are highly specialized parasites that interact with their host plants using a range of strategies. The esophageal glands are the main places where nematodes synthesize effector proteins, which play central roles in successful invasion. The Meloidogyne incognita effector MiISE5 is exclusively expressed within the subventral esophageal cells and is upregulated during early parasitic stages. In this study, we show that MiISE5 can be secreted to barley cells through infectious hyphae of Magnaporthe oryzae. Transgenic Arabidopsis plants expressing MiISE5 became significantly more susceptible to M. incognita. Inversely, the tobacco rattle virus (TRV)-mediated silence of MiISE5 decreased nematode parasitism. Moreover, transient expression of MiISE5 suppressed cell death caused by Burkholderia glumae in Nicotiana benthamiana. Based on transcriptome analysis of MiISE5 transgenic sample and the wild-type (WT) sample, we obtained 261 DEGs, and the results of GO and KEGG enrichment analysis indicate that MiISE5 can interfere with various metabolic and signaling pathways, especially the JA signaling pathway, to facilitate nematode parasitism. Results from the present study suggest that MiISE5 plays an important role during the early stages of parasitism and provides evidence to decipher the molecular mechanisms underlying the manipulation of host immune defense responses by M. incognita.

Aboveground herbivory induced jasmonates disproportionately reduce plant reproductive potential by facilitating root nematode infestation

Different plant feeders, including insects and parasitic nematodes, can influence each other by triggering systemic changes in their shared host plants. In most cases, however, the underlying mechanisms are unclear, and the consequences for plant fitness are not well understood. We studied the interaction between leaf feeding Manduca sexta caterpillars and root parasitic nematodes in Nicotiana attenuata. Simulated M. sexta attack increased the abundance of root parasitic nematodes in the field and facilitated Meloidogyne incognita reproduction in the glasshouse. Intact jasmonate biosynthesis was found to be required for both effects. Flower counts revealed that the jasmonate-dependent facilitation of nematode infestation following simulated leaf attack reduces the plant's reproductive potential to a greater degree than would be expected from the additive effects of the individual stresses. This work reveals that jasmonates mediate the interaction between a leaf herbivore and root parasitic nematodes and illustrates how plant-mediated interactions can alter plant's reproductive potential. The selection pressure resulting from the demonstrated fitness effects is likely to influence the evolution of plant defense traits in nature.

Gibberellin antagonizes jasmonate-induced defense against Meloidogyne graminicola in rice

Gibberellin (GA) regulates various plant growth and developmental processes, but its role in pathogen attack, and especially nematode-plant interactions, still remains to be elucidated. An in-depth characterization of the role of GA in nematode infection was conducted using mutant lines of rice, chemical inhibitors, and phytohormone measurements. Our results showed that GA influences rice-Meloidogyne graminicola interactions in a concentration-dependent manner. Foliar spray of plants with a low concentration of gibberellic acid enhanced nematode infection. Biosynthetic and signaling mutants confirmed the importance of gibberellin for rice susceptibility to M. graminicola infection. Our study also demonstrates that GA signaling suppresses jasmonate (JA)-mediated defense against M. graminicola, and likewise the JA-induced defense against M. graminicola requires SLENDER RICE1 (SLR1)-mediated repression of the GA pathway. In contrast to observations from other plant-pathogen interactions, GA plays a dominant role over JA in determining susceptibility to M. graminicola in rice. This GA-induced nematode susceptibility was largely independent of auxin biosynthesis, but relied on auxin transport. In conclusion, we showed that GA-JA antagonistic crosstalk is at the forefront of the interaction between rice and M. graminicola, and SLR1 plays a central role in the JA-mediated defense response in rice against this nematode.

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.

Red Light-Induced Systemic Resistance Against Root-Knot Nematode Is Mediated by a Coordinated Regulation of Salicylic Acid, Jasmonic Acid and Redox Signaling in Watermelon

Red light (RL) can stimulate plant defense against foliar diseases; however, its role in activation of systemic defense against root diseases remains unclear. Here, the effect of RL on root knot nematode Meloidogyne incognita (RKN) infestation was investigated in watermelon plants (Citrullus lanatus L.). Plants were exposed to 200 μmol m^-2 s^-1 photosynthetic photon flux density RL at the canopy level for 21 days using light-emitting photodiodes. The results showed that RL significantly suppressed gall formation and nematode development, which was closely associated with the RL-induced attenuation of oxidative stress in roots. Gene expression analysis showed that RL caused a transient upregulation of PR1 and WRKY70 transcripts at 7 days post inoculation in RKN-infected plants. Further investigation revealed that RL-induced systemic defense against RKN was attributed to increased jasmonic acid (JA) and salicylic acid (SA) content, and transcript levels of their biosynthetic genes in roots. Interestingly, while malondialdehyde content decreased, H₂O₂ accumulation increased in RL-treated RKN-plants, indicating a potential signaling role of H₂O₂ in mediating RL-induced systemic defense. Furthermore, analysis of enzymatic and non-enzymatic antidoxidants revealed that RL-induced enhanced defense agaist RKN was also attributed to increased activities of antioxidant enzymes as well as redox homeostasis. Taken together, these findings suggest that RL could enhance systemic resistance against RKN, which is mediated by a coordinated regulation of JA- and SA-dependent signaling, antioxidants, and redox homeostasis in watermelon plants.

The Novel Secreted Meloidogyne incognita Effector MiISE6 Targets the Host Nucleus and Facilitates Parasitism in Arabidopsis

Meloidogyne incognita is highly specialized parasite that interacts with host plants using a range of strategies. The effectors are synthesized in the esophageal glands and secreted into plant cells through a needle-like stylet during parasitism. In this study, based on RNA-seq and bioinformatics analysis, we predicted 110 putative Meloidogyne incognita effectors that contain nuclear localization signals (NLSs). Combining the Burkholderia glumae-pEDV based screening system with subcellular localization, from 20 randomly selected NLS effector candidates, we identified an effector MiISE6 that can effectively suppress B. glumae-induced cell death in Nicotiana benthamiana, targets to the nuclei of plant cells, and is highly expressed in early parasitic J2 stage. Sequence analysis showed that MiISE6 is a 157-amino acid peptide, with an OGFr_N domain and two NLS motifs. Hybridization in situ verified that MiISE6 is expressed in the subventral esophageal glands. Yeast invertase secretion assay validated the function of the signal peptide harbored in MiISE6. Transgenic Arabidopsis thaliana plants expressing MiISE6 become more susceptible to M. incognita. Inversely, the host-derived RNAi of MiISE6 of the nematode can decrease its parasitism on host. Based on transcriptome analysis of the MiISE6 transgenic Arabidopsis samples and the wild-type samples, we obtained 852 differentially expressed genes (DEGs). Integrating Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, we found that expression of MiISE6 in Arabidopsis can suppress jasmonate signaling pathway. In addition, the expression of genes related to cell wall modification and the ubiquitination proteasome pathway also have detectable changes in the transgenic plants. Results from the present study suggest that MiISE6 is involved in interaction between nematode-plant, and plays an important role during the early stages of parasitism by interfering multiple signaling pathways of plant. Moreover, we found homologs of MiISE6 in other sedentary nematodes, Meloidogyne hapla and Globodera pallida. Our experimental results provide evidence to decipher the molecular mechanisms underlying the manipulation of host immune defense responses by plant parasitic nematodes, and transcriptome data also provide useful information for further study nematode-plant interactions.

Agrobacteria Enhance Plant Defense Against Root-Knot Nematodes on Tomato

The increased incidence of the crown gall disease caused by Agrobacterium tumefaciens has long been associated with activities of root-knot nematodes (Meloidogyne spp.). Pot experiments on tomato were designed to assess plant vitality, nematode reproduction, and crown gall incidence in combined infection with Agrobacterium and Meloidogyne spp. on tomato roots. Results suggest that tomato plants infected with pathogenic A. tumefaciens 2 days before the nematodes show enhanced plant defense against M. ethiopica resulting in lower egg and gall counts on roots 45 and 90 days postinoculation (dpi); no significantly enhanced defense was observed when the plant was inoculated with bacteria and nematodes at the same time. Split-root experiments also showed that the observed interaction was systemic. Reverse-transcription quantitative polymerase chain reaction analysis that targeted several genes under plant hormonal control suggests that the suppression was mediated via systemic acquired resistance by the pathogenesis-related protein 1 and that M. ethiopica did not enhance the defense reaction of tomato against Agrobacterium spp. Nematodes completely inhibited tumor growth in a 45-day experiment if inoculated onto the roots before the pathogenic bacteria. We conclude that the observed antagonism in the tested pathosystem was the result of initially strong plant defense that was later suppressed by the invading pathogen and pest.

Isolation and functional characterization of a methyl jasmonate-responsive 3-carene synthase from Lavandula x intermedia

A methyl jasmonate responsive 3-carene synthase (Li3CARS) gene was isolated from Lavandula x intermedia and functionally characterized in vitro. Lavenders produce essential oils consisting mainly of monoterpenes, including the potent antimicrobial and insecticidal monoterpene 3-carene. In this study we isolated and functionally characterized a leaf-specific, methyl jasmonate (MeJA)-responsive monoterpene synthase (Li3CARS) from Lavandula x intermedia. The ORF excluding transit peptides encoded a 64.9 kDa protein that was expressed in E. coli, and purified with Ni-NTA agarose affinity chromatography. The recombinant Li3CARS converted GPP into 3-carene as the major product, with K _m and k _cat of 3.69 ± 1.17 µM and 2.01 s^-1 respectively. Li3CARS also accepted NPP as a substrate to produce multiple products including a small amount of 3-carene. The catalytic efficiency of Li3CARS to produce 3-carene was over ten fold higher for GPP (k _cat /K _m = 0.56 µM^-1s^-1) than NPP (k _cat /K _m = 0.044 µM^-1s^-1). Production of distinct end product profiles from different substrates (GPP versus NPP) by Li3CARS indicates that monoterpene metabolism may be controlled in part through substrate availability. Li3CARS transcripts were found to be highly abundant in leaves (16-fold) as compared to flower tissues. The transcriptional activity of Li3CARS correlated with 3-carene production, and was up-regulated (1.18- to 3.8-fold) with MeJA 8-72 h post-treatment. The results suggest that Li3CARS may have a defensive role in Lavandula.

Shifting from priming of salicylic acid- to jasmonic acid-regulated defences by Trichoderma protects tomato against the root knot nematode Meloidogyne incognita

Beneficial root endophytes such as Trichoderma spp. can reduce infections by parasitic nematodes through triggering host defences. Little is currently known about the complex hormone signalling underlying the induction of resistance. In this study, we investigated whether Trichoderma modulates the hormone signalling network in the host to induce resistance to nematodes. We investigated the role and the timing of the jasmonic acid (JA)- and salicylic acid (SA)-regulated defensive pathways in Trichoderma-induced resistance to the root knot nematode Meloidogyne incognita. A split-root system of tomato (Solanum lycopersicum) was used to study local and systemic induced defences by analysing nematode performance, defence gene expression, responsiveness to exogenous hormone application, and dependence on SA and JA signalling of Trichoderma-induced resistance. Root colonization by Trichoderma impeded nematode performance both locally and systemically at multiple stages of the parasitism, that is, invasion, galling and reproduction. First, Trichoderma primed SA-regulated defences, which limited nematode root invasion. Then, Trichoderma enhanced JA-regulated defences, thereby antagonizing the deregulation of JA-dependent immunity by the nematodes, which compromised galling and fecundity. Our results show that Trichoderma primes SA- and JA-dependent defences in roots, and that the priming of responsiveness to these hormones upon nematode attack is plastic and adaptive to the parasitism stage.

Exogenous application of methyl jasmonate induces defence against Meloidogyne hapla in soybean

Phytohormones play important roles in plant defence against plant-parasitic nematodes, although the role of jasmonate (JA) in defence against root-knot nematodes (RKN, Meloidogyne spp.) in soybean (Glycine max) was unknown. In this study, two commercial soybean cultivars, cvs DongSheng1 (DS1) and SuiNong14 (SN14), were identified as susceptible and resistant, respectively, to M. hapla. Quantitative reverse transcription (qRT)-PCR analysis showed that the expression of genes involved in JA synthesis or signalling was significantly induced in both susceptible and resistant roots at 24 and 48 h after inoculation. Exogenous application of methyl jasmonate induced defence against RKN in susceptible cv. DS1, which might be involved in altered activities of defence-related enzymes (chitinase and β-1,3 glucanase) and pathogenesis-related gene PR5 expression. The results indicate that exogenous application of JA might be an alternative strategy to induce soybean resistance against RKN.

Direct nematicidal effects of methyl jasmonate and acibenzolar-S-methyl against Meloidogyne incognita

The aim of this study was to examine the nematicidal properties of two defence inducers against the root-knot nematode Meloidogyne incognita. A direct-contact bioassay was applied to evaluate the nematicidal effects of acibenzolar-S-methyl (ASM) and methyl jasmonate (MEJA) on second-stage juveniles (J2). Nematodes were incubated in different concentrations of these compounds, and the numbers of immobile nematodes were counted after 24 and 48 h post incubation. Tap water was then added to verify whether the nematodes recovered or remained dead at 72 h. The percentage of dead nematodes was used as indicator for the toxicity of the different solutions. Our results show that ASM, in the formulation of Bion®, and MEJA have nematicidal properties.

Plant-Mediated Systemic Interactions Between Pathogens, Parasitic Nematodes, and Herbivores Above- and Belowground

Plants are important mediators of interactions between aboveground (AG) and belowground (BG) pathogens, arthropod herbivores, and nematodes (phytophages). We highlight recent progress in our understanding of within- and cross-compartment plant responses to these groups of phytophages in terms of altered resource dynamics and defense signaling and activation. We review studies documenting the outcome of cross-compartment interactions between these phytophage groups and show patterns of cross-compartment facilitation as well as cross-compartment induced resistance. Studies involving soilborne pathogens and foliar nematodes are scant. We further highlight the important role of defense signaling loops between shoots and roots to activate a full resistance complement. Moreover, manipulation of such loops by phytophages affects systemic interactions with other plant feeders. Finally, cross-compartment-induced changes in root defenses and root exudates extend systemic defense loops into the rhizosphere, enhancing or reducing recruitment of microbes that induce systemic resistance but also affecting interactions with root-feeding phytophages.

A Novel Meloidogyne incognita Effector Misp12 Suppresses Plant Defense Response at Latter Stages of Nematode Parasitism

Secreted effectors in plant root-knot nematodes (RKNs, or Meloidogyne spp.) play key roles in their parasite processes. Currently identified effectors mainly focus on the early stage of the nematode parasitism. There are only a few reports describing effectors that function in the latter stage. In this study, we identified a potential RKN effector gene, Misp12, that functioned during the latter stage of parasitism. Misp12 was unique in the Meloidogyne spp., and highly conserved in Meloidogyne incognita. It encoded a secretory protein that specifically expressed in the dorsal esophageal gland, and highly up-regulated during the female stages. Transient expression of Misp12-GUS-GFP in onion epidermal cell showed that Misp12 was localized in cytoplast. In addition, in planta RNA interference targeting Misp12 suppressed the expression of Misp12 in nematodes and attenuated parasitic ability of M. incognita. Furthermore, up-regulation of jasmonic acid (JA) and salicylic acid (SA) pathway defense-related genes in the virus-induced silencing of Misp12 plants, and down-regulation of SA pathway defense-related genes in Misp12-expressing plants indicated the gene might be associated with the suppression of the plant defense response. These results demonstrated that the novel nematode effector Misp12 played a critical role at latter parasitism of M. incognita.

Plant immunity induced by COS-OGA elicitor is a cumulative process that involves salicylic acid

Plant innate immunity offers considerable opportunities for plant protection but beside flagellin and chitin, not many molecules and their receptors have been extensively characterized and very few have successfully reached the field. COS-OGA, an elicitor that combines cationic chitosan oligomers (COS) with anionic pectin oligomers (OGA), efficiently protected tomato (Solanum lycopersicum) grown in greenhouse against powdery mildew (Leveillula taurica). Leaf proteomic analysis of plants sprayed with COS-OGA showed accumulation of Pathogenesis-Related proteins (PR), especially subtilisin-like proteases. qRT-PCR confirmed upregulation of PR-proteins and salicylic acid (SA)-related genes while expression of jasmonic acid/ethylene-associated genes was not modified. SA concentration and class III peroxidase activity were increased in leaves and appeared to be a cumulative process dependent on the number of sprayings with the elicitor. These results suggest a systemic acquired resistance (SAR) mechanism of action of the COS-OGA elicitor and highlight the importance of repeated applications to ensure efficient protection against disease.

Jasmonic acid carboxyl methyltransferase regulates development and herbivory-induced defense response in rice

Jasmonic acid (JA) and related metabolites play a key role in plant defense and growth. JA carboxyl methyltransferase (JMT) may be involved in plant defense and development by methylating JA to methyl jasmonate (MeJA) and thus influencing the concentrations of JA and related metabolites. However, no JMT gene has been well characterized in monocotyledon defense and development at the molecular level. After we cloned a rice JMT gene, OsJMT1, whose encoding protein was localized in the cytosol, we found that the recombinant OsJMT1 protein catalyzed JA to MeJA. OsJMT1 is up-regulated in response to infestation with the brown planthopper (BPH; Nilaparvata lugens). Plants in which OsJMT1 had been overexpressed (oe-JMT plants) showed reduced height and yield. These oe-JMT plants also exhibited increased MeJA levels but reduced levels of herbivore-induced JA and jasmonoyl-isoleucine (JA-Ile). The oe-JMT plants were more attractive to BPH female adults but showed increased resistance to BPH nymphs, probably owing to the different responses of BPH female adults and nymphs to the changes in levels of H2 O2 and MeJA in oe-JMT plants. These results indicate that OsJMT1, by altering levels of JA and related metabolites, plays a role in regulating plant development and herbivore-induced defense responses in rice.

Optimizing Chemically Induced Resistance in Tomato Against Botrytis cinerea

Resistance-inducing chemicals can offer broad-spectrum disease protection in crops, but can also affect plant growth and interactions with plant-beneficial microbes. We have evaluated different application methods of β-aminobutyric acid (BABA) and jasmonic acid (JA) for long-lasting induced resistance in tomato against Botrytis cinerea. In addition, we have studied nontarget effects on plant growth and root colonization by arbuscular mycorrhizal fungi (AMF). Germinating seeds for 1 week in BABA- or JA-containing solutions promoted seed germination efficiency, did not affect plant growth, and induced resistance in 4-week-old plants. When formulating BABA and JA in carboxymethyl cellulose seed coating, only BABA was able to induce resistance in 4-week-old plants. Root treatment of 1-week-old seedlings with BABA or JA also induced resistance in 4-week-old plants. However, this seedling treatment repressed plant growth at higher concentrations of the chemicals, which was particularly pronounced in hydroponically grown plants after BABA treatment. Both seed coating with BABA, and seedling treatments with BABA or JA, did not affect AMF root colonization in soil-grown tomato. Our study has identified commercially feasible application methods of BABA and JA, which induce durable disease resistance in tomato without concurrent impacts on plant growth or colonization by plant-beneficial AMF.

Gall-forming root-knot nematodes hijack key plant cellular functions to induce multinucleate and hypertrophied feeding cells

Among plant-parasitic nematodes, the root-knot nematodes (RKNs) of the Meloidogyne spp. are the most economically important genus. RKN are root parasitic worms able to infect nearly all crop species and have a wide geographic distribution. During infection, RKNs establish and maintain an intimate relationship with the host plant. This includes the creation of a specialized nutritional structure composed of multinucleate and hypertrophied giant cells, which result from the redifferentiation of vascular root cells. Giant cells constitute the sole source of nutrients for the nematode and are essential for growth and reproduction. Hyperplasia of surrounding root cells leads to the formation of the gall or root-knot, an easily recognized symptom of plant infection by RKNs. Secreted effectors produced in nematode salivary glands and injected into plant cells through a specialized feeding structure called the stylet play a critical role in the formation of giant cells. Here, we describe the complex interactions between RKNs and their host plants. We highlight progress in understanding host plant responses, focusing on how RKNs manipulate key plant processes and functions, including cell cycle, defence, hormones, cellular scaffold, metabolism and transport.

OPDA Has Key Role in Regulating Plant Susceptibility to the Root-Knot Nematode Meloidogyne hapla in Arabidopsis

Jasmonic acid (JA) is a plant hormone that plays important roles in regulating plant defenses against necrotrophic pathogens and herbivorous insects, but the role of JA in mediating the plant responses to root-knot nematodes has been unclear. Here we show that an application of either methyl jasmonate (MeJA) or the JA-mimic coronatine (COR) on Arabidopsis significantly reduced the number of galls caused by the root-knot nematode Meloidogyne hapla. Interestingly, the MeJA-induced resistance was independent of the JA-receptor COI1 (CORONATINE INSENSITIVE 1). The MeJA-treated plants accumulated the JA precursor cis-(+)-12-oxo-phytodienoic acid (OPDA) in addition to JA/JA-Isoleucine, indicating a positive feedback loop in JA biosynthesis. Using mutants in the JA-biosynthetic pathway, we found that plants deficient in the biosynthesis of JA and OPDA were hyper-susceptible to M. hapla. However, the opr3 mutant, which cannot convert OPDA to JA, exhibited wild-type levels of nematode galling. In addition, mutants in the JA-biosynthesis and perception which lie downstream of opr3 also displayed wild-type levels of galling. The data put OPR3 (OPDA reductase 3) as the branch point between hyper-susceptibility and wild-type like levels of disease. Overall, the data suggests that the JA precursor, OPDA, plays a role in regulating plant defense against nematodes.

Transcriptome Analysis of Cotton (Gossypium hirsutum L.) Genotypes That Are Susceptible, Resistant, and Hypersensitive to Reniform Nematode (Rotylenchulus reniformis)

Reniform nematode is a semi-endoparasitic nematode species causing significant yield loss in numerous crops, including cotton (Gossypium hirsutum L.). An RNA-sequencing analysis was conducted to measure transcript abundance in reniform nematode susceptible (DP90 & SG747), resistant (BARBREN-713), and hypersensitive (LONREN-1) genotypes of cotton (Gossypium hirsutum L.) with and without reniform nematode infestation. Over 90 million trimmed high quality reads were assembled into 84,711 and 80, 353 transcripts using the G. arboreum and the G. raimondii genomes as references. Many transcripts were significantly differentially expressed between the three different genotypes both prior to and during nematode pathogenesis, including transcripts corresponding to the gene ontology categories of cell wall, hormone metabolism and signaling, redox reactions, secondary metabolism, transcriptional regulation, stress responses, and signaling. Further analysis revealed that a number of these differentially expressed transcripts mapped to the G. raimondii and/or the G. arboreum genomes within 1 megabase of quantitative trait loci that had previously been linked to reniform nematode resistance. Several resistance genes encoding proteins known to be strongly linked to pathogen perception and resistance, including LRR-like and NBS-LRR domain-containing proteins, were among the differentially expressed transcripts mapping near these quantitative trait loci. Further investigation is required to confirm a role for these transcripts in reniform nematode susceptibility, hypersensitivity, and/or resistance. This study presents the first systemic investigation of reniform nematode resistance-associated genes using different genotypes of cotton. The candidate reniform nematode resistance-associated genes identified in this study can serve as the basis for further functional analysis and aid in further development of reniform a nematode resistant cotton germplasm.

Transcription of Biotic Stress Associated Genes in White Clover (Trifolium repens L.) Differs in Response to Cyst and Root-Knot Nematode Infection

The transcription of four members of the Kunitz proteinase inhibitor (KPI) gene family of white clover (Trifolium repens L.), designated as Tr-KPI1, Tr-KPI2, Tr-KPI4 and Tr-KPI5, was investigated at both local infection (roots) and systemic (leaf tissue) sites in white clover in response to infection with the clover root knot nematode (CRKN) Meloidogyne trifoliophila and the clover cyst nematode (CCN) Heterodera trifolii. Invasion by the CRKN resulted in a significant decrease in transcript abundance of Tr-KPI4 locally at both 4 days post-infection (dpi) and at 8 dpi, and an increase in transcription of Tr-KPI1 systemically at 8 dpi. In contrast, an increase in transcript abundance of all four Tr-KPI genes locally at 4 and 8 dpi, and an increase of Tr-KPI1, Tr-KPI2, and Tr-KPI5 at 8 dpi systemically was observed in response to infection with the CCN. Challenge of a resistant (R) genotype and a susceptible (S) genotype of white clover with the CCN revealed a significant increase in transcript abundance of all four Tr-KPI genes locally in the R genotype, while an increase in abundance of only Tr-KPI1, Tr-KPI2, and Tr-KPI5 was observed in the S genotype, and only at 4 dpi. The transcript abundance of a member of the1-AMINOCYCLOPROPANE-1-CARBOXYLATE (ACC) SYNTHASE gene family from white clover (Tr-ACS1) was significantly down-regulated locally in response to CRKN infection at 4 and 8 dpi and at 4 dpi, systemically, while abundance increased locally and systemically at 8 dpi in response to CCN challenge. Conversely, the abundance of the jasmonic acid (JA) signalling gene, CORONATINE-INSENSITIVE PROTEIN 1 from white clover (Tr-COI1) increased significantly at 8 dpi locally in response to CRKN infection, but decreased at 8 dpi in response to CCN infection. The significance of this differential regulation of transcription is discussed with respect to differences in infection strategy of the two nematode species.

Identification of Ramie Genes in Response to Pratylenchus coffeae Infection Challenge by Digital Gene Expression Analysis

Root lesion disease, caused by Pratylenchus coffeae, seriously impairs the growth and yield of ramie, an important natural fiber crop. The ramie defense mechanism against P. coffeae infection is poorly understood, which hinders efforts to improve resistance via breeding programs. In this study, the transcriptome of the resistant ramie cultivar Qingdaye was characterized using Illumina sequence technology. About 46.3 million clean pair end (PE) reads were generated and assembled into 40,826 unigenes with a mean length of 830 bp. Digital gene expression (DGE) analysis was performed on both the control roots (CK) and P. coffeae-challenged roots (CH), and the differentially expressed genes (DEGs) were identified. Approximately 10.16 and 8.07 million cDNA reads in the CK and CH cDNA libraries were sequenced, respectively. A total of 137 genes exhibited different transcript abundances between the two libraries. Among them, the expressions of 117 and 20 DEGs were up- and down-regulated in P. coffeae-challenged ramie, respectively. The expression patterns of 15 candidate genes determined by qRT-PCR confirmed the results of DGE analysis. Time-course expression profiles of eight defense-related genes in susceptible and resistant ramie cultivars were different after P. coffeae inoculation. The differential expression of protease inhibitors, pathogenesis-related proteins (PRs), and transcription factors in resistant and susceptible ramie during P. coffeae infection indicated that cystatin likely plays an important role in nematode resistance.

Identification of jasmonic acid-associated microRNAs and characterization of the regulatory roles of the miR319/TCP4 module under root-knot nematode stress in tomato

MicroRNAs (miRNAs) are important transcriptional and post-transcriptional modulators of gene expression that play crucial roles in the responses to diverse stresses. To explore jasmonic acid (JA)-dependent miRNA-mediated regulatory networks that are responsive to root-knot nematode (RKN), two small RNA libraries were constructed from wild-type (WT) and JA mutant (spr2) plants. A total of 263 known miRNAs and 441 novel miRNAs were significantly regulated under RKN stress in the two libraries. The spatio-temporal expression of candidate miRNAs and their corresponding targets were analysed by qRT-PCR under RKN stress. A clear negative correlation was observed between miR319 and its target TEOSINTE BRANCHED1/CYCLOIDEA/PRO-LIFERATING CELL FACTOR 4 (TCP4) in leaf, stem, and root under RKN stress, implying that the miR319/TCP4 module is involved in the systemic defensive response. Reverse genetics demonstrated that the miR319/TCP4 module affected JA synthetic genes and the endogenous JA level in leaves, thereby mediating RKN resistance. These results suggested that the action of miR319 in serving as a systemic signal responder and regulator that modulated the RKN systemic defensive response was mediated via JA. The potential cross-talk between miR319/TCP4 and miR396/GRF (GROWTH RESPONDING FACTOR) in roots under RKN invasion is discussed, and a predictive model regarding miR319/TCP4-mediated RKN resistance is proposed.

Exogenous application of methyl jasmonate induces a defense response and resistance against Sclerotinia sclerotiorum in dry bean plants

Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic fungal pathogen that causes a disease known as white mold, which is a major problem for dry bean (Phaseolus vulgaris L.) and other crops in many growing areas in Brazil. To investigate the role of methyl jasmonate (MeJA) in defending dry bean plants against S. sclerotiorum, we used suppression subtractive hybridization (SSH) of cDNA and identified genes that are differentially expressed during plant-pathogen interactions after treatment. Exogenous MeJA application enhanced resistance to the pathogen, and SSH analyses led to the identification of 94 unigenes, presumably involved in a variety of functions, which were classified into several functional categories, including metabolism, signal transduction, protein biogenesis and degradation, and cell defense and rescue. Using RT-qPCR, some unigenes were found to be differentially expressed in a time-dependent manner in dry bean plants during the interaction with S. sclerotiorum after MeJA treatment, including the pathogenesis-related protein PR3 (chitinase), PvCallose (callose synthase), PvNBS-LRR (NBS-LRR resistance-like protein), PvF-box (F-box family protein-like), and a polygalacturonase inhibitor protein (PGIP). Based on these expression data, the putative roles of differentially expressed genes were discussed in relation to the disease and MeJA resistance induction. Changes in the activity of the pathogenesis-related proteins β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase, and peroxidase in plants after MeJA treatment and following inoculation of the pathogen were also investigated as molecular markers of induced resistance. Foliar application of MeJA induced partial resistance against S. sclerotiorum in plants as well as a consistent increase in pathogenesis-related protein activities. Our findings provide new insights into the physiological and molecular mechanisms of resistance induced by MeJA in the P. vulgaris-S. sclerotiorum pathosystem.