Signal Transduction in Plant⁻Nematode Interactions

Antagonistic Bacteria Bacillus velezensis VB7 Possess Nematicidal Action and Induce an Immune Response to Suppress the Infection of Root-Knot Nematode (RKN) in Tomato

Meloidogyne incognita, the root-knot nematode (RKN), a devastating plant parasitic nematode, causes considerable damage to agricultural crops worldwide. As a sedentary root parasite, it alters the root's physiology and influences the host's phytohormonal signaling to evade defense. The sustainable management of RKN remains a challenging task. Hence, we made an attempt to investigate the nematicide activity of Bacillus velezensis VB7 to trigger the innate immune response against the infection of RKN. In vitro assay, B. velezensis VB7 inhibited the hatchability of root-knot nematode eggs and juvenile mortality of M. incognita by 87.95% and 96.66%, respectively at 96 hrs. The application of B. velezensis VB7 challenged against RKN induced MAMP-triggered immunity via the expression of transcription factors/defense genes by several folds pertaining to WRKY, LOX, PAL, MYB, and PR in comparison to those RKN-inoculated and healthy control through RT-PCR. Additionally, Cytoscape analysis of defense genes indicated the coordinated expression of various other genes linked to immune response. Thus, the current study clearly demonstrated the effectiveness of B. velezensis VB7 as a potential nematicide and inducer of immune responses against RKN infestation in tomato.

Comparative Transcriptome Analysis Reveals the Specific Activation of Defense Pathways Against Globodera pallida in Gpa2 Resistant Potato Roots

Cyst nematodes are considered a dominant threat to yield for a wide range of major food crops. Current control strategies are mainly dependent on crop rotation and the use of resistant cultivars. Various crops exhibit single dominant resistance (R) genes that are able to activate effective host-specific resistance to certain cyst nematode species and/or populations. An example is the potato R gene Gpa2, which confers resistance against the potato cyst nematode (PCN), Globodera pallida population D383. Activation of Gpa2 results in a delayed resistance response, which is characterized by a layer of necrotic cells formed around the developing nematode feeding structure. However, knowledge about the Gpa2-induced defense pathways is still lacking. Here, we uncover the transcriptional changes and gene expression network induced upon Gpa2 activation in potato roots infected with G. pallida. To this end, in vitro-grown Gpa2-resistant potato roots were infected with the avirulent population D383 and virulent population Rookmaker. Infected root segments were harvested at 3 and 6 dpi and sent for RNA sequencing. Comparative transcriptomics revealed a total of 1,743 differentially expressed genes (DEGs) upon nematode infection, of which 559 DEGs were specifically regulated in response to D383 infection. D383-specific DEGs associated with Gpa2-mediated defense mainly relates to calcium-binding activity, salicylic acid (SA) biosynthesis, and systemic acquired resistance (SAR). These data reveal that cyst nematode resistance in potato roots depends on conserved downstream signaling pathways involved in plant immunity, which are also known to contribute to R genes-mediated resistance against other pathogens with different lifestyles.

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.

Fluoroalkenyl-Grafted Chitosan Oligosaccharide Derivative: An Exploration for Control Nematode Meloidogyne Incognita

The exploration of novel, environmentally friendly, and efficient nematicides is essential, and modifying natural biomacromolecules is one feasible approach. In this study, 6-O-(trifluorobutenyl-oxadiazol)-chitosan oligosaccharide derivative was synthesized and characterized by FTIR, NMR, and TG/DTG. Its bioactivity and action mode against root-knot nematode M. incognita were estimated. The results show that the derivative shows high nematicidal activity against J2s, and egg hatching inhibitory activity at 1 mg/mL. The derivative may affect nematode ROS metabolism and further damage intestinal tissue to kill nematode. Meanwhile, by synergism with improving crop resistance, the derivative performed a high control effect on the nematode with low phytotoxicity. These findings suggested that chitosan oligosaccharide derivatives bearing fluoroalkenyl groups are promising green nematicides.

Minc03328 effector gene downregulation severely affects Meloidogyne incognita parasitism in transgenic Arabidopsis thaliana

Minc03328 effector gene downregulation triggered by in planta RNAi strategy strongly reduced plant susceptibility to Meloidogyne incognita and suggests that Minc03328 gene is a promising target for the development of genetically engineered crops to improve plant tolerance to M. incognita. Meloidogyne incognita is the most economically important species of root-knot nematodes (RKN) and causes severe damage to crops worldwide. M. incognita secretes several effector proteins to suppress the host plant defense response, and manipulate the plant cell cycle and other plant processes facilitating its parasitism. Different secreted effector proteins have already been identified in M. incognita, but not all have been characterized or have had the confirmation of their involvement in nematode parasitism in their host plants. Herein, we characterized the Minc03328 (Minc3s00020g01299) effector gene, confirmed its higher expression in the early stages of M. incognita parasitism in plants, as well as the accumulation of the Minc03328 effector protein in subventral glands and its secretion. We also discuss the potential for simultaneous downregulation of its paralogue Minc3s00083g03984 gene. Using the in planta RNA interference strategy, Arabidopsis thaliana plants overexpressing double-stranded RNA (dsRNA) were generated to specifically targeting and downregulating the Minc03328 gene during nematode parasitism. Transgenic Minc03328-dsRNA lines that significantly downregulated Minc03328 gene expression during M. incognita parasitism were significantly less susceptible. The number of galls, egg masses, and [galls/egg masses] ratio were reduced in these transgenic lines by up to 85%, 90%, and 87%, respectively. Transgenic Minc03328-dsRNA lines showed the presence of fewer and smaller galls, indicating that parasitism was hindered. Overall, data herein strongly suggest that Minc03328 effector protein is important for M. incognita parasitism establishment. As well, the in planta Minc03328-dsRNA strategy demonstrated high biotechnological potential for developing crop species that could efficiently control RKN in the field.

Identification of Repellents from Four Non-Host Asteraceae Plants for the Root Knot Nematode, Meloidogyne incognita

Olfactory cues guide plant parasitic nematodes (PPNs) to their host plants. We tested the hypothesis that non-host plant root volatiles repel PPNs. To achieve this, we compared the olfactory responses of infective juveniles (J2s) of the PPN Meloidogyne incognita to four non-host Asteraceae plants, namely, black-jack (Bidens pilosa), pyrethrum (Chrysanthemum cinerariifolium), marigold (Tagetes minuta), and sweet wormwood (Artemisia annua), traditionally used in sub-Saharan Africa for the management of PPNs. Chemical analysis by coupled gas chromatography-mass spectrometry (GC/MS) combined with random forest analysis, followed by behavioral assays, identified the repellents in the root volatiles of B. pilosa, T. minuta, and A. annua as (E)-β-farnesene and 1,8-cineole, whereas camphor was attractive. In contrast, random forest analysis predicted repellents for C. cinerariifolium and A. annua as β-patchoulene and isopropyl hexadecanoate. Our results suggested that terpenoids generally account for the repellency of non-host Asteraceae plants used in PPN management.

Minc00344 and Mj-NULG1a effectors interact with GmHub10 protein to promote the soybean parasitism by Meloidogyne incognita and M. javanica

Several economically important crops are susceptible to root-knot nematode (RKNs). Meloidogyne incognita and M. javanica are the two most reported species from the RKN complex, causing damage to several crops worldwide. The successful outcome of the Meloidogyne-plant interaction is associated with molecular factors secreted by the nematode to suppress the plant's immune response and promote nematode parasitism. In contrast, several plant factors are associated with defense against nematode infection. In this study, we identified and characterized the specific interaction of Minc00344 and Mj-NULG1a effectors with soybean GmHub10 (Glyma.19G008200) protein in vitro and in vivo. An Arabidopsis thaliana T-DNA mutant of AtHub10 (AT3G27960, an orthologous gene of GmHub10) showed higher susceptibility to M. incognita. Thus, since soybean and A. thaliana Hub10 proteins are involved in pollen tube growth and indirect activation of the defense response, our data suggest that effector-Hub10 interactions could be associated with an increase in plant susceptibility. These findings indicate the potential of these effector proteins to develop new biotechnological tools based on RNA interference and the overexpression of engineered Hub10 proteins for the efficient management of RKN in crops.

Plant-parasitic nematodes affecting vegetable crops in greenhouses

This work focuses on investigating plant-parasitic nematodes that affect greenhouse vegetables. The study took place in the Rostov region (Russian Federation) between May 2019 and May 2020 and involved 180 samples of soil and roots of 30 different vegetables in the families Cucurbitaceae (6), Solanaceae (8), Umbelliferae (8), Lamiaceae (4) and Allioideae (4) from 20 intensive farming locations. In this study, 11 nematode genera were detected. The most common genus was Meloidogyne, followed by Helicotylenchus, Pratylenchus, and Scutellonema. The highest Meloidogyne densities were detected in cucumbers, green peppers, carrots, eggplants, basil, and celery. Onions were not infected with Meloidogyne at all. Plant diseases caused by Pratylenchus, Scutellonema and Helicotylenchus were present in 29.7%, 51.5% and 81.6% of all crops examined, respectively. Xiphinema were found exclusively in carrots and celery, while Ditylenchus were only present in tomatoes and carrots (for each, the prevalence was 2.1%). The relative abundance of Meloidogyne, Helicotylenchus, and Pratylenchus was 58.3%, 10.4%, and 2.1%, respectively. As regards other genera, the relative abundance was less than 1%. The results show that soil properties are as important for the abundance, distribution and structure of the plant-parasitic nematode communities as the host plant. Findings may be helpful in improving the vegetable pest controls.

Genetic toolbox and regulatory circuits of plant-nematode associations

Plant-nematode associations are the most imperative area of study that forms the basis to understand their regulatory networks and coordinated functional aspects. Nematodes are highly parasitic organisms known so far, to cause relentless damage towards agricultural crops on a global scale. They pierce the roots of host plants and form neo-plastic feeding structures to extract out resources for their functional development. Moreover, they undergo re-differentiation within plant cells to form giant multi-nucleate feeding structures or syncytium. All these processes are facilitated by numerous transcriptomic, proteomic, metabolomic and epigenetic modifications, that regulate different biological attractions among plants and nematodes. Nevertheless, these mechanisms are quite remarkable and have been explored in the present review. Here, we have shed light on genomic as well as genetic approaches to acquire an effective understanding regarding plant-nematode associations. Transcriptomics have revealed an extensive network to unravel feeding mechanism of nematodes through gene-expression programming of target genes. Also, the regulatory circuits of epigenetic alterations through DNA-methylation, non-coding RNAs and histone modifications very well explain epigenetic profiling within plants. Since decades, research have observed many intricacies to elucidate the dynamic nature of epigenetic modulations in plant-nematode attractions. By this review, we have highlighted the functional aspects of small RNAs in inducing plant-nematode parasitism along with the putative role of miRNAs. These RNAs act as chief genetic elements to mediate the expressional changes in plants through post-transcriptional silencing of various effector proteins as well as transcriptional factors. A pragmatic role of miRNAs in modulating gene expression in nematode infection and feeding site development have also been reviewed. Hence, they have been considered master regulators for functional reprogramming the expression during establishment of feeding sites. We have also encapsulated the advancement of genome-broadened DNA-methylation and untangled the nematode mediated dynamic alterations within plant methylome along with assessing transcriptional activities of various genes and transposons. In particular, we have highlighted the role of effector proteins in stimulating epigenetic changes. Finally, we have emerged towards a molecular-based core understanding about plant-nematode associations.

PAL-mediated SA biosynthesis pathway contributes to nematode resistance in wheat

The pathogen cereal cyst nematode (CCN) is deleterious to Triticeae crops and is a threat to the global crop yield. Accession no. 1 of Aegilops variabilis, a relative of Triticum aestivum (bread wheat), is highly resistant to CCN. Our previous study demonstrated that the expression of the phenylalanine ammonia lyase (PAL) gene AevPAL1 in Ae. variabilis is strongly induced by CCN. PAL, the first enzyme of phenylpropanoid metabolism, is involved in abiotic and biotic stress responses. However, its role in plant-CCN interaction remains unknown. In the present study, we proved that AevPAL1 helps to confer CCN resistance through affecting the synthesis of salicylic acid (SA) and downstream secondary metabolites. The silencing of AevPAL1 increased the incidence of CCN infection in roots and decreased the accumulation of SA and phenylalanine (Phe)-derived specialized metabolites. The exogenous pre-application of SA also improved CCN resistance. Additionally, the functions of PAL in phenylpropanoid metabolism correlated with tryptophan decarboxylase (TDC) functioning in tryptophan metabolism pathways. The silencing of either AevPAL1 or AevTDC1 exhibited a concomitant reduction in the expression of both genes and the contents of metabolites downstream of PAL and TDC. These results suggested that AevPAL1, possibly in coordination with AevTDC1, positively contributes to CCN resistance by altering the downstream secondary metabolites and SA content in Ae. variabilis. Moreover, AevPAL1 overexpression significantly enhanced CCN resistance in bread wheat and did not exhibit significant negative effects on yield-related traits, suggesting that AevPAL1 is valuable for the genetic improvement of CCN resistance in bread wheat.

Novel resistance strategies to soybean cyst nematode (SCN) in wild soybean

Soybean cyst nematode (SCN, Heterodera glycine Ichinohe) is the most damaging soybean pest worldwide and management of SCN remains challenging. The current SCN resistant soybean cultivars, mainly developed from the cultivated soybean gene pool, are losing resistance due to SCN race shifts. The domestication process and modern breeding practices of soybean cultivars often involve strong selection for desired agronomic traits, and thus, decreased genetic variation in modern cultivars, which consequently resulted in limited sources of SCN resistance. Wild soybean (Glycine soja) is the wild ancestor of cultivated soybean (Glycine max) and it's gene pool is indisputably more diverse than G. max. Our aim is to identify novel resistant genetic resources from wild soybean for the development of new SCN resistant cultivars. In this study, resistance response to HG type 2.5.7 (race 5) of SCN was investigated in a newly identified SCN resistant ecotype, NRS100. To understand the resistance mechanism in this ecotype, we compared RNA seq-based transcriptomes of NRS100 with two SCN-susceptible accessions of G. soja and G. max, as well as an extensively studied SCN resistant cultivar, Peking, under both control and nematode J2-treated conditions. The proposed mechanisms of resistance in NRS100 includes the suppression of the jasmonic acid (JA) signaling pathway in order to allow for salicylic acid (SA) signaling-activated resistance response and polyamine synthesis to promote structural integrity of root cell walls. Our study identifies a set of novel candidate genes and associated pathways involved in SCN resistance and the finding provides insight into the mechanism of SCN resistance in wild soybean, advancing the understanding of resistance and the use of wild soybean-sourced resistance for soybean improvement.

Plants Specifically Modulate the Microbiome of Root-Lesion Nematodes in the Rhizosphere, Affecting Their Fitness

Plant-parasitic nematodes are a major constraint on agricultural production. They significantly impede crop yield. To complete their parasitism, they need to locate, disguise, and interact with plant signals exuded in the rhizosphere of the host plant. A specific subset of the soil microbiome can attach to the surface of nematodes in a specific manner. We hypothesized that host plants recruit species of microbes as helpers against attacking nematode species, and that these helpers differ among plant species. We investigated to what extend the attached microbial species are determined by plant species, their root exudates, and how these microbes affect nematodes. We conditioned the soil microbiome in the rhizosphere of different plant species, then employed culture-independent and culture-dependent methods to study microbial attachment to the cuticle of the phytonematode Pratylenchus penetrans. Community fingerprints of nematode-attached fungi and bacteria showed that the plant species govern the microbiome associated with the nematode cuticle. Bacteria isolated from the cuticle belonged to Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Sphingobacteria, and Firmicutes. The isolates Microbacterium sp. i.14, Lysobacter capsici i.17, and Alcaligenes sp. i.37 showed the highest attachment rates to the cuticle. The isolates Bacillus cereus i.24 and L. capsici i.17 significantly antagonized P. penetrans after attachment. Significantly more bacteria attached to P. penetrans in microbiome suspensions from bulk soil or oat rhizosphere compared to Ethiopian mustard rhizosphere. However, the latter caused a better suppression of the nematode. Conditioning the cuticle of P. penetrans with root exudates significantly decreased the number of Microbacterium sp. i.14 attaching to the cuticle, suggesting induced changes of the cuticle structure. These findings will lead to a more knowledge-driven exploitation of microbial antagonists of plant-parasitic nematodes for plant protection.

Occurrence and molecular characterization of Meloidogyne graminicola on rice in Central Punjab, Pakistan

Meloidogyne graminicola threatens global rice production, yet is understudied for many areas where it is cultivated. To better understand the prevalence and incidence of M. graminicola in central Punjab, Pakistan, we carried out field surveys of rice fields in the districts of Faisalabad and Chiniot. M. graminicola isolates were recovered from soil and root samples and identified on the basis of perineal patterns and rDNA ITS-based sequencing. The severity of nematode attack on rice roots and infested fields at various locations was based on galling index, root-knot nematode juveniles per root system, juveniles per 100 ml of soil, and prevalence of stylet-bearing nematodes and non-stylet-bearing nematodes. Maximum prevalence (22.5 and 27.5%) and minimum prevalence (17.5 and 20%) of M. graminicola was observed in Chiniot and Faisalabad, respectively. Eleven alternate host-plant species were examined in this study revealing varying degrees of M. graminicola infestation. ITS sequencing and phylogenetic analysis indicated that isolates from this study form a well-resolved clade with others from Asia, while another isolate falls outside of this clade in an unresolved polytomy with those from Europe and South America. Though monophyletic with the other M. graminicola, the isolates from Pakistan are distinguished by their high genetic variability and long branch lengths relative to the other isolates of M. graminicola, suggesting Pakistan as a possible ancestral area. Our results indicate that rice is severely attacked by a genetically diverse and aggressive M. graminicola, necessitating the development of appropriate control measures for its management in rice and other graminaceous crops.

Harnessing the plant microbiome to promote the growth of agricultural crops

The rhizosphere microbiome is composed of diverse microbial organisms, including archaea, viruses, fungi, bacteria as well as eukaryotic microorganisms, which occupy a narrow region of soil directly associated with plant roots. The interactions between these microorganisms and the plant can be commensal, beneficial or pathogenic. These microorganisms can also interact with each other, either competitively or synergistically. Promoting plant growth by harnessing the soil microbiome holds tremendous potential for providing an environmentally friendly solution to the increasing food demands of the world's rapidly growing population, while also helping to alleviate the associated environmental and societal issues of large-scale food production. There recently have been many studies on the disease suppression and plant growth promoting abilities of the rhizosphere microbiome; however, these findings largely have not been translated into the field. Therefore, additional research into the dynamic interactions between crop plants, the rhizosphere microbiome and the environment are necessary to better guide the harnessing of the microbiome to increase crop yield and quality. This review explores the biotic and abiotic interactions that occur within the plant's rhizosphere as well as current agricultural practices, and how these biotic and abiotic factors, as well as human practices, impact the plant microbiome. Additionally, some limitations, safety considerations, and future directions to the study of the plant microbiome are discussed.

Transfer cells: what regulates the development of their intricate wall labyrinths?

Transfer cells (TCs) support high nutrient rates into, or at symplasmic discontinuities within, the plant body. Their transport capacity is conferred by an amplified plasma membrane surface area, enriched in nutrient transporters, supported on an intricately invaginated wall labyrinth (WL). Thus, development of the WL is at the heart of TC function. Enquiry has shifted from describing WL architecture and formation to discovering mechanisms regulating WL assembly. Experimental systems used to examine these phenomena are critiqued. Considerable progress has been made in identifying master regulators that commit stem cells to a TC fate (e.g. the maize Myeloblastosis (MYB)-related R1-type transcription factor) and signals that induce differentiated cells to undergo trans-differentiation to a TC phenotype (e.g. sugar, auxin and ethylene). In addition, signals that provide positional information for assembly of the WL include apoplasmic hydrogen peroxide and cytosolic Ca²⁺ plumes. The former switches on, and specifies the intracellular site for WL construction, while the latter creates subdomains to direct assembly of WL invaginations. Less is known about macromolecule species and their spatial organization essential for WL assembly. Emerging evidence points to a dependency on methyl-esterified homogalacturonan accumulation, unique patterns of cellulose and callose deposition and spatial positioning of arabinogalactan proteins.

Compounds Associated with Infection by the Root-Knot Nematode, Meloidogyne javanica, Influence the Ability of Infective Juveniles to Recognize Host Plants

Plant root chemistry is altered by the parasitism of plant-parasitic nematodes (PPN). Here, we investigated the influence of the infective stage juveniles (J2) of Meloidogyne javanica in inducing tomato (Solanum lycopersicum) root volatiles and chemotactic effect on conspecifics. In olfactometer assays, J2 avoided the roots of 2-day infected plants but preferred 7-day-infected tomato compared to healthy plants. Chemical analysis showed a 2-7-fold increase in the amounts of monoterpenes emitted from tomato roots infected with M. javanica relative to healthy roots. In further bioassays, the monoterpenes β-pinene, (+)-(2)-carene, α-phellandrene, and β-phellandrene differentially attracted (51-87%) J2 relative to control. Concurrent reduction and increase in the levels of methyl salicylate and (Z)-methyl dihydrojasmonate, respectively, in the root volatiles reduced J2 responses. These results demonstrate that the host plant can alter its root volatile composition to inhibit PPN attack. The observed plant-produced inhibition of J2 warrants further investigation as a potential management tool for growers.

Biological Control of Plant-Parasitic Nematodes by Filamentous Fungi Inducers of Resistance: Trichoderma, Mycorrhizal and Endophytic Fungi

Plant-parasitic-nematodes represent a major threat to the agricultural production of different crops worldwide. Due to the high toxicity of chemical nematicides, it is necessary to develop new control strategies against nematodes. In this respect, filamentous fungi can be an interesting biocontrol alternative. The genus Trichoderma, mycorrhizal and endophytic fungi are the main groups of filamentous fungi studied and used as biological control agents (BCAs) against nematodes as resistance inducers. They are able to reduce the damage caused by plant-parasitic nematodes directly by parasitism, antibiosis, paralysis and by the production of lytic enzymes. But they also minimize harm by space and resource-competition, by providing higher nutrient and water uptake to the plant, or by modifying the root morphology, and/or rhizosphere interactions, that constitutes an advantage for the plant-growth. Besides, filamentous fungi are able to induce resistance against nematodes by activating hormone-mediated (salicylic and jasmonic acid, strigolactones among others) plant-defense mechanisms. Additionally, the alteration of the transport of chemical defense components through the plant or the synthesis of plant secondary metabolites and different enzymes can also contribute to enhancing plant defenses. Therefore, the use of filamentous fungi of the mentioned groups as BCAs is a promising durable biocontrol strategy in agriculture against plant-parasitic nematodes.

Plant tumors: a hundred years of study

The review provides information on the mechanisms underlying the development of spontaneous and pathogen-induced tumors in higher plants. The activation of meristem-specific regulators in plant tumors of various origins suggests the meristem-like nature of abnormal plant hyperplasia. Plant tumor formation has more than a century of research history. The study of this phenomenon has led to a number of important discoveries, including the development of the Agrobacterium-mediated transformation technique and the discovery of horizontal gene transfer from bacteria to plants. There are two main groups of plant tumors: pathogen-induced tumors (e.g., tumors induced by bacteria, viruses, fungi, insects, etc.), and spontaneous ones, which are formed in the absence of any pathogen in plants with certain genotypes (e.g., interspecific hybrids, inbred lines, and mutants). The causes of the transition of plant cells to tumor growth are different from those in animals, and they include the disturbance of phytohormonal balance and the acquisition of meristematic characteristics by differentiated cells. The aim of this review is to discuss the mechanisms underlying the development of most known examples of plant tumors.

Transcriptomic and Metabolomic Changes Triggered by Fusarium solani in Common Bean (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) is a major legume and is frequently attacked by fungal pathogens, including Fusarium solani f. sp. phaseoli (FSP), which cause Fusarium root rot. FSP substantially reduces common bean yields across the world, including China, but little is known about how common bean plants defend themselves against this fungal pathogen. In the current study, we combined next-generation RNA sequencing and metabolomics techniques to investigate the changes in gene expression and metabolomic processes in common bean infected with FSP. There were 29,722 differentially regulated genes and 300 differentially regulated metabolites between control and infected plants. The combined omics approach revealed that FSP is perceived by PAMP-triggered immunity and effector-triggered immunity. Infected seedlings showed that common bean responded by cell wall modification, ROS generation, and a synergistic hormone-driven defense response. Further analysis showed that FSP induced energy metabolism, nitrogen mobilization, accumulation of sugars, and arginine and proline metabolism. Importantly, metabolic pathways were most significantly enriched, which resulted in increased levels of metabolites that were involved in the plant defense response. A correspondence between the transcript pattern and metabolite profile was observed in the discussed pathways. The combined omics approach enhances our understanding of the less explored pathosystem and will provide clues for the development of common bean cultivars' resistant to FSP.

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.

Piriformospora indica promotes cucumber tolerance against Root-knot nematode by modulating photosynthesis and innate responsive genes

Root Knot Nematode (RKN, Meloidogyne incognita) is one of the greatest damaging soil pathogens causes severe yield losses in cucumber and many other economic crops. Here, we evaluated the potential antagonistic effect of the root mutualistic fungus Piriformospora indica against RKN and their impact on vegetative growth, yield, photosynthesis, endogenous salicylic acid (SA) and its responsive genes. Our results showed that P. indica dramatically decreased the damage on shoot and root architecture of cucumber plants, which consequently enhanced yield of infested plants. Likewise, P. indica colonization clearly improved the chlorophyll content and delimited the negative impact of RNK on photosynthesis. Moreover, P. indica colonization exhibited a significant reduction of different vital nematological parameters such as soil larva density, amount of eggs/eggmass, eggmasses, females and amount of galls at cucumber roots. Additionally, the results showed that SA level was significantly increased generally in the roots of all treatments especially in plants infested with RKN alone as compared to control. This suggests that P. indica promoting SA levels in host cucumber plant roots to antagonize the RKN and alleviate severity damages occurred in its roots. This higher levels of SA in cucumber roots was consistent with the higher expressional levels of SA pathway genes PR1 and PR3. Furthermore, P. indica colonization reduces PR1, PR3 and increased NPR1 in roots of RKN infested cucumber plants when compared to non-colonized plants. Interestingly, our in vitro results showed that direct application of P. indica suspension against the J2s exhibited a significant increase in mortality ratio. Our results collectively suggest that P. indica promoting morphological, physiological and SA levels that might together play a major important role to alleviate the adverse impact of RKN in cucumber.

Screening and identification of a non-peptide antagonist for the peptide hormone receptor in Arabidopsis

Intercellular signaling mediated by peptide hormones and membrane-localized receptor kinases plays crucial roles in plant developmental processes. Because of their diverse functions, agonistic or antagonistic modulation of peptide signaling holds enormous promise for agricultural applications. Here we established a high-throughput screening system using a bead-immobilized receptor kinase and fluorescent-labeled peptide ligand to identify small molecules that bind peptide hormone receptors in competition with natural ligands. We used the Arabidopsis CLE9-BAM1 ligand-receptor pair to screen a library of ≈30,000 chemicals and identified NPD12704 as an antagonist for BAM1. NPD12704 also inhibited CLV3 binding to BAM1 but only minimally interfered with CLV3 binding to CLV1, the closest homolog of BAM1, demonstrating preferential receptor specificity. Treatment of clv1-101 mutant seedlings with NPD12704 enhanced the enlarged shoot apical meristem phenotype. Our results provide a technological framework enabling high-throughput identification of small non-peptide chemicals that specifically control receptor kinase–mediated peptide hormone signaling in plants.

Hidefumi Shinohara and colleagues used the CLE9-BAM1 ligand-receptor pair as a model system for screening peptide hormone receptor-binding small molecules in plants. They identified the small molecule NPD12704 as an antagonist for BAM1 and demonstrated the specific regulatory activity of NPD12704 in shoot apical meristem.

Resistance to Cereal Cyst Nematodes in Wheat and Barley: An Emphasis on Classical and Modern Approaches

Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals like wheat and barley. These nematodes alone are estimated to reduce production of crops by 10% globally. This necessitates a huge enhancement of nematode resistance in cereal crops against CCNs. Nematode resistance in wheat and barley in combination with higher grain yields has been a preferential research area for cereal nematologists. This usually involved the targeted genetic exploitations through natural means of classical selection breeding of resistant genotypes and finding quantitative trait luci (QTLs) associated with resistance genes. These improvements were based on available genetic diversity among the crop plants. Recently, genome-wide association studies have widely been exploited to associate nematode resistance or susceptibility with particular regions of the genome. Use of biotechnological tools through the application of various transgenic strategies for enhancement of nematode resistance in various crop plants including wheat and barley had also been an important area of research. These modern approaches primarily include the use of gene silencing, exploitation of nematode effector genes, proteinase inhibitors, chemodisruptive peptides and a combination of one or more of these approaches. Furthermore, the perspective genome editing technologies including CRISPR-Cas9 could also be helpful for improving CCN resistance in wheat and barley. The information provided in this review will be helpful to enhance resistance against CCNs and will attract the attention of the scientific community towards this neglected area.