Heterodera Schachtii Research Articles

Glutathione contributes to plant defence against parasitic cyst nematodes.

Cyst nematodes (CNs) are an important group of root‐infecting sedentary endoparasites that severely damage many crop plants worldwide. An infective CN juvenile enters the host's roots and migrates towards the vascular cylinder, where it induces the formation of syncytial feeding cells, which nourish the CN throughout its parasitic stages. Here, we examined the role of glutathione (l‐γ‐glutamyl‐l‐cysteinyl‐glycine) in Arabidopsis thaliana on infection with the CN Heterodera schachtii. Arabidopsis lines with mutations pad2, cad2, or zir1 in the glutamate–cysteine ligase (GSH1) gene, which encodes the first enzyme in the glutathione biosynthetic pathway, displayed enhanced CN susceptibility, but susceptibility was reduced for rax1, another GSH1 allele. Biochemical analysis revealed differentially altered thiol levels in these mutants that was independent of nematode infection. All glutathione‐deficient mutants exhibited impaired activation of defence marker genes as well as genes for biosynthesis of the antimicrobial compound camalexin early in infection. Further analysis revealed a link between glutathione‐mediated plant resistance to CN infection and the production of camalexin on nematode infection. These results suggest that glutathione levels affect plant resistance to CN by fine‐tuning the balance between the cellular redox environment and the production of compounds related to defence against infection.

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.

Characterization of an Arabidopsis Defensin-like Gene Conferring Resistance against Nematodes.

Arabidopsis contains 317 genes for defensin-like (DEFL) peptides. DEFLs have been grouped into different families based mainly on cysteine motifs. The DEFL0770 group contains seven genes, of which four are strongly expressed in roots. We found that the expression of these genes is downregulated in syncytia induced by the beet cyst nematode Heterodera schachtii as revealed by RNAseq analysis. We have studied one gene of this group, At3g59930, in detail. A promoter::GUS line revealed that the gene is only expressed in roots but not in other plant organs. Infection of the GUS line with larvae of H. schachtii showed a strong downregulation of GUS expression in infection sites as early as 1 dpi, confirming the RNAseq data. The At3g59930 peptide had only weak antimicrobial activity against Botrytis cinerea. Overexpression lines had no enhanced resistance against this fungus but were more resistant to H. schachtii infection. Our data indicate that At3g59930 is involved in resistance to nematodes which is probably not due to direct nematicidal activity.

Registration of sugar beet mapping populations CN239, CN240, and CN241 segregating for resistance to Heterodera schachtii from sea beet

AbstractSugar beet (Beta vulgaris L.) mapping populations CN239 (Reg. no. MP‐1, NSL 540835 MAP), CN240 (Reg. no. MP‐2, NSL 540836 MAP), and CN241 (Reg. no. MP‐3, NSL 540837 MAP) segregate for sugar beet cyst nematode (SBCN) resistance and were developed by the USDA‐ARS at Salinas, CA. Our first objective was to compare soil for greenhouse screening: naturally infested (SBCN‐infested field) and artificially inoculated (pasteurized with Heterodera schachtii cysts added). Commercial and USDA‐ARS lines were grown in each diluted to 20 cysts g−1. Each was rinsed to collect cysts. The USDA‐ARS lines were kept until cyst counts were completed, in preparation for the second objective: make crosses with individuals of known SBCN reaction. A beet plant can have thousands of flowers, making traits heterogenous. For genetic studies, resistance must be confirmed prior to crossing, or progeny could have unexpected segregation. 7927‐4‐308D seedlings with low cyst counts (2–17 cysts) were selected as the SBCN‐resistant donor parent in mapping populations CN239, CN240, and CN241. 7927‐4‐308D resistance is derived from composite crosses between sugar beet and over 40 Beta vulgaris subsp. maritima (L.) Arcang. accessions. CN239 combined 7927‐4‐308D with 0747 (elite line) plants with high counts (115–148 cysts). CN240 combined 7927‐4‐308D with CN12‐446 (SBCN resistant) plants with low counts (11–26 cysts). Allelism between 7927‐4‐308D and CN12‐446 is undetermined. CN241 combined 7927‐4‐308D with a 7927‐4‐309E plant with high count (54 cysts). 7927‐4‐309E is a sister line of 7927‐4‐308D but is SBCN susceptible.

Screening of Resistant Genotypes of Sugar Beet to Sugar Beet Cyst Nematode and Beet Curly Top Virus and Underlying Biochemical Mechanisms Involved in Their Resistance

Screening of Resistant Genotypes of Sugar Beet to Sugar Beet Cyst Nematode and Beet Curly Top Virus and Underlying Biochemical Mechanisms Involved in Their Resistance

Development of a Species-Specific SCAR-PCR Assay for Direct Detection of Sugar Beet Cyst Nematode (Heterodera schachtii) from Infected Roots and Soil Samples.

Sugar beet cyst nematode (SBCN, Heterodera schachtii) is an important nematode that causes significant yield losses of 25–50% or more in most areas of sugar beet production worldwide. Rapid and accurate identification of this species is essential to support decisions on pest management. However, the difference between H. schachtii and other Heterodera spp. based on morphology is a challenging task. In the present study, a SCAR-PCR assay was developed to identify and differentiate H. schachtii in infected root and soil samples. H. schachtii-species-specific SCAR-PCR primers OPA06-HsF and OPA06-HsR were designed from the randomly amplified polymorphic DNA (RAPD) marker amplified with random primer OPA06. The developed primers specifically amplify a 922-bp fragment from the target populations but did not amplify DNA from non-target cyst nematodes including Heterodera, Globodera, Cactodera, and other related species tested in this study. The sensitivity detection indicated that 5 × 10−4 of a single cyst, 1/320 of a single second-stage juvenile (J2), or 10 pg of genomic DNA could be detected. The assay accurately identifies the different stages of H. schachtii in sugar beet and oilseed rape roots as well as a single J2 in 10 g of soil. Finally, the SCAR-PCR assay detected H. schachtii in seven samples out of the fifteen field samples. The assay will not only be useful for differentiating H. schachtii from mixed populations of Heterodera spp. but also for effective detection of the species directly from infested samples. The assay also requires no expertise in the taxonomy and morphology of the species but serves to improve the diagnosis of H. schachtii in infested fields.

Developing a Real-Time PCR Assay for Direct Identification and Quantification of Soybean Cyst Nematode, Heterodera glycines, in Soil and Its Discrimination from Sugar Beet Cyst Nematode, Heterodera schachtii.

The soybean cyst nematode (SCN) Heterodera glycines continues to be a major threat to soybean production worldwide. Morphological discrimination between SCN and other nematodes of the Heterodera schachtii sensu stricto group is not only difficult and time-consuming but also requires high expertise in nematode taxonomy. Molecular assays were developed to differentiate SCN from sugar beet cyst nematode (SBCN) and other nematodes and to quantify SCN directly from DNA extracts of field soils. SCN- and SBCN-specific quantitative real-time PCR (qPCR) primers were designed from a nematode-secreted CLAVATA gene and used for these assays. The primers were evaluated on the basis of target specificity to SCN or SBCN using DNA from 20 isolates of SCN and 32 isolates of other plant-parasitic nematodes. A standard curve relating threshold cycle and log values of nematode numbers was generated from artificially infested soils and was used to quantify SCN in naturally infested field soils. There was a high correlation between the SCN numbers estimated from naturally infested field soils by conventional methods, and the numbers quantified using the SYBR Green I-based qPCR assay. The qPCR assay is highly specific and sensitive and provides improved SCN detection sensitivity down to 1 SCN egg in 20 g of soil (10 eggs/200 g soil). This assay is useful for efficient detection and quantification of SCN directly from field soil. Species-specific conventional PCR assays were also developed each for SCN and SBCN, alongside a qPCR assay that simultaneously discriminates SCN from SBCN. These assays require no expertise in nematode taxonomy and morphology, and they may serve as useful diagnostic tools in research, diagnostic laboratories, and extension services for SCN management. Sensitive and accurate detection and quantification of SCN are essential for recommending effective management measures against SCN. We also investigated the impact of soil texture and nematode life stage on molecular quantification of SCN.

Rapid and Visual Detection of Heterodera schachtii Using Recombinase Polymerase Amplification Combined with Cas12a-Mediated Technology.

Heterodera schachtii is a well-known cyst nematode that causes serious economic losses in sugar beet production every year. Rapid and visual detection of H. schachtii is essential for more effective prevention and control. In this study, a species-specific recombinase polymerase amplification (RPA) primer was designed from a specific H. schachtii sequence-characterized amplified region (SCAR) marker. A band was obtained in reactions with DNA from H. schachtii, but absent from nontarget cyst nematodes. The RPA results could be observed by the naked eye, using a lateral flow dipstick (LFD). Moreover, we combined CRISPR technology with RPA to identify positive samples by fluorescence detection. Sensitivity analysis indicated that 10−4 single cysts and single females, 4−3 single second-stage juveniles, and a 0.001 ng genomic DNA template could be detected. The sensitivity of the RPA method for H. schachtii detection is not only higher than that of PCR and qPCR, but can also provide results in <1 h. Consequently, the RPA assay is a practical and useful diagnostic tool for early diagnosis of plant tissues infested by H. schachtii. Sugar beet nematodes were successfully detected in seven of 15 field sugar beet root samples using the RPA assay. These results were consistent with those achieved by conventional PCR, indicating 100% accuracy of the RPA assay in field samples. The RPA assay developed in the present study has the potential for use in the direct detection of H. schachtii infestation in the field.

Host status of several green manure crops to &lt;i&gt;Heterodera schachtii&lt;/i&gt; and green manure crop cultivation effect on nematode density

Host status of several green manure crops to &lt;i&gt;Heterodera schachtii&lt;/i&gt; and green manure crop cultivation effect on nematode density

Metabolic Analysis of the Development of the Plant-Parasitic Cyst Nematodes Heterodera schachtii and Heterodera trifolii by Capillary Electrophoresis Time-of-Flight Mass Spectrometry.

The cyst nematodes Heterodera schachtii and Heterodera trifolii, whose major hosts are sugar beet and clover, respectively, damage a broad range of plants, resulting in significant economic losses. Nematodes synthesize metabolites for organismal development and social communication. We performed metabolic profiling of H. schachtii and H. trifolii in the egg, juvenile 2 (J2), and female stages. In all, 392 peaks were analyzed by capillary electrophoresis time-of-flight mass spectrometry, which revealed a lot of similarities among metabolomes. Aromatic amino acid metabolism, carbohydrate metabolism, choline metabolism, methionine salvage pathway, glutamate metabolism, urea cycle, glycolysis, gluconeogenesis, coenzyme metabolism, purine metabolism, pyrimidine metabolism, and tricarboxylic acid (TCA) cycle for energy conversion (β-oxidation and branched-chain amino acid metabolism) energy storage were involved in all stages studied. The egg and female stages synthesized higher levels of metabolites compared to the J2 stage. The key metabolites detected were glycerol, guanosine, hydroxyproline, citric acid, phosphorylcholine, and the essential amino acids Phe, Leu, Ser, and Val. Metabolites, such as hydroxyproline, acetylcholine, serotonin, glutathione, and glutathione disulfide, which are associated with growth and reproduction, mobility, and neurotransmission, predominated in the J2 stage. Other metabolites, such as SAM, 3PSer, 3-ureidopropionic acid, CTP, UDP, UTP, 3-hydroxy-3-methylglutaric acid, 2-amino-2-(hydroxymethyl-1,3-propanediol, 2-hydroxy-4-methylvaleric acid, Gly Asp, glucuronic acid-3 + galacturonic acid-3 Ser-Glu, citrulline, and γ-Glu-Asn, were highly detected in the egg stage. Meanwhile, nicotinamide, 3-PG, F6P, Cys, ADP-Ribose, Ru5P, S7P, IMP, DAP, diethanolamine, p-Hydroxybenzoic acid, and γ-Glu-Arg_divalent were unique to the J2 stage. Formiminoglutamic acid, nicotinaminde riboside + XC0089, putrescine, thiamine 2,3-dihydroxybenzoic acid, 3-methyladenine, caffeic acid, ferulic acid, m-hydrobenzoic acid, o- and p-coumaric acid, and shikimic acid were specific to the female stage. Overall, highly similar identities and quantities of metabolites between the corresponding stages of the two species of nematode were observed. Our results will be a valuable resource for further studies of physiological changes related to the development of nematodes and nematode–plant interactions.

Marasmius oreades agglutinin enhances resistance of Arabidopsis against plant-parasitic nematodes and a herbivorous insect

BackgroundPlant-parasitic nematodes and herbivorous insects have a significant negative impact on global crop production. A successful approach to protect crops from these pests is the in planta expression of nematotoxic or entomotoxic proteins such as crystal proteins from Bacillus thuringiensis (Bt) or plant lectins. However, the efficacy of this approach is threatened by emergence of resistance in nematode and insect populations to these proteins. To solve this problem, novel nematotoxic and entomotoxic proteins are needed. During the last two decades, several cytoplasmic lectins from mushrooms with nematicidal and insecticidal activity have been characterized. In this study, we tested the potential of Marasmius oreades agglutinin (MOA) to furnish Arabidopsis plants with resistance towards three economically important crop pests: the two plant-parasitic nematodes Heterodera schachtii and Meloidogyne incognita and the herbivorous diamondback moth Plutella xylostella.ResultsThe expression of MOA does not affect plant growth under axenic conditions which is an essential parameter in the engineering of genetically modified crops. The transgenic Arabidopsis lines showed nearly complete resistance to H. schachtii, in that the number of female and male nematodes per cm root was reduced by 86–91 % and 43–93 % compared to WT, respectively. M. incognita proved to be less susceptible to the MOA protein in that 18–25 % and 26–35 % less galls and nematode egg masses, respectively, were observed in the transgenic lines. Larvae of the herbivorous P. xylostella foraging on MOA-expression lines showed a lower relative mass gain (22–38 %) and survival rate (15–24 %) than those feeding on WT plants.ConclusionsThe results of our in planta experiments reveal a robust nematicidal and insecticidal activity of the fungal lectin MOA against important agricultural pests which may be exploited for crop protection.

Impact of the genetic diversity of three cyst nematodes on the effectiveness of root exudates to induce hatching

Cyst nematodes are sedentary endoparasites of plants which cause important economic losses worldwide. New nematode control measures are needed since the removal of effective chemical nematicides from the market due to their negative impact on environment and human health. Induced hatching of second-stage juveniles in the absence of host plant using root exudates, also named “suicide hatching”, could be a sustainable alternative method to reduce nematode population densities in infested soils. Unfortunately, biocontrol methods are often less effective in agricultural fields than in laboratory or greenhouse and this could be due to, among other reasons, a different susceptibility of nematode populations to root exudate stimulation. Testing this intra-specific variability would help to anticipate any drop in the efficiency of this new biocontrol strategy. A selection of root exudates from different plant species, maximizing the hatching level highlighted in a previous study, was tested on the hatching of representative populations of the genetic diversity for Globodera pallida, Heterodera schachtii and Heterodera carotae. Results showed significant differences between populations for given nematode species but not correlated with the genetic structure. Overall, root exudates tested provide a high level of hatching of these three nematode species. Surprisingly, the root exudate from broccoli induces hatching of European populations of the potato cyst nematode G. pallida.

Bacillus firmus I-1582 promotes plant growth and impairs infection and development of the cyst nematode Heterodera schachtii over two generations

Plant-parasitic nematodes wreak havoc on crops by root parasitism worldwide. An approach to combat nematode root parasitism is the application of antagonistic microbes like the rhizobacterium Bacillus firmus I-1582 which is promoted as biological control agent. Although B. firmus is a known nematode antagonist in general, the underlying mechanisms about its interaction with nematodes and plants have not yet been elucidated. Therefore, we explored the influence of B. firmus I-1582 as well as its extracellular and secreted molecules on plant–nematode interaction utilizing the plant–pathogen system Arabidopsis thaliana–Heterodera schachtii. We demonstrated that B. firmus I-1582 is attracted by A. thaliana root exudates, particularly by those of young plants. The bacterium colonized the root and showed a strictly pH-dependent development and plant growth promotion effect. Our results revealed that root colonization by B. firmus I-1582 significantly protected A. thaliana from infestation by the beet cyst nematode whereas dead bacterial cells or the culture supernatant were not effective. The bacterium also negatively affected nematode reproduction as well as pathogenicity and development of next generation nematodes. The obtained results highlight B. firmus I-1582 as a promising biocontrol agent that is well suited as an element of integrated control management strategies in sustainable agriculture.

Arabidopsis thaliana Myb59 Gene Is Involved in the Response to Heterodera schachtii Infestation, and Its Overexpression Disturbs Regular Development of Nematode-Induced Syncytia.

Transcription factors are proteins that directly bind to regulatory sequences of genes to modulate and adjust plants’ responses to different stimuli including biotic and abiotic stresses. Sedentary plant parasitic nematodes, such as beet cyst nematode, Heterodera schachtii, have developed molecular tools to reprogram plant cell metabolism via the sophisticated manipulation of genes expression, to allow root invasion and the induction of a sequence of structural and physiological changes in plant tissues, leading to the formation of permanent feeding sites composed of modified plant cells (commonly called a syncytium). Here, we report on the AtMYB59 gene encoding putative MYB transcription factor that is downregulated in syncytia, as confirmed by RT-PCR and a promoter pMyb59::GUS activity assays. The constitutive overexpression of AtMYB59 led to the reduction in A. thaliana susceptibility, as indicated by decreased numbers of developed females, and to the disturbed development of nematode-induced syncytia. In contrast, mutant lines with a silenced expression of AtMYB59 were more susceptible to this parasite. The involvement of ABA in the modulation of AtMYB59 gene transcription appears feasible by several ABA-responsive cis regulatory elements, which were identified in silico in the gene promoter sequence, and experimental assays showed the induction of AtMYB59 transcription after ABA treatment. Based on these results, we suggest that AtMYB59 plays an important role in the successful parasitism of H. schachtii on A. thaliana roots.

Conserved Opposite Functions in Plant Resistance to Biotrophic and Necrotrophic Pathogens of the Immune Regulator SRFR1.

Plant immunity is mediated in large part by specific interactions between a host resistance protein and a pathogen effector protein, named effector-triggered immunity (ETI). ETI needs to be tightly controlled both positively and negatively to enable normal plant growth because constitutively activated defense responses are detrimental to the host. In previous work, we reported that mutations in SUPPRESSOR OF rps4-RLD1 (SRFR1), identified in a suppressor screen, reactivated EDS1-dependent ETI to Pseudomonas syringae pv. tomato (Pto) DC3000. Besides, mutations in SRFR1 boosted defense responses to the generalist chewing insect Spodoptera exigua and the sugar beet cyst nematode Heterodera schachtii. Here, we show that mutations in SRFR1 enhance susceptibility to the fungal necrotrophs Fusarium oxysporum f. sp. lycopersici (FOL) and Botrytis cinerea in Arabidopsis. To translate knowledge obtained in AtSRFR1 research to crops, we generated SlSRFR1 alleles in tomato using a CRISPR/Cas9 system. Interestingly, slsrfr1 mutants increased expression of SA-pathway defense genes and enhanced resistance to Pto DC3000. In contrast, slsrfr1 mutants elevated susceptibility to FOL. Together, these data suggest that SRFR1 is functionally conserved in both Arabidopsis and tomato and functions antagonistically as a negative regulator to (hemi-) biotrophic pathogens and a positive regulator to necrotrophic pathogens.

THE PROBLEM OF SUGAR BEET CYST NEMATODES IN MODERN CONDITIONS OF MACROECONOMIC AND CLIMATIC CHALLENGES

In this work, the current state of infection of the cultivated areas of sugar beet farms with the sugar beet cyst nematode Heterodera schachtii is considered. After the systemic crisis of agricultural production in the early 90th, the practice of operating Russian sugar factories not using domestic (sugar beet) but imported (cane) raw materials was widespread. For many years, in the absence of a host plant in the fields, the population density of highly specialized phytohelminths naturally decreased to an economically imperceptible level. However, in accordance with the principle of irreversibility of soil biocontamination of agroecosystems, the nematode retained its presence due to the mechanisms of mesobiosis and the maintenance of the population on reserve weeds. After the strategic course taken in 2014 towards import substitution, sugar beet areas (usually around sugar factories) returned to the main crop, and in 2018, for the first time in its history, Russia even became a sugar exporting country. However, the technological regulations of the USSR, mostly crop rotations were not observed and the nematode problem was again actualized, first of all, in the Chernozem and Krasnodar region. The proposed model of the dynamics of the population density of the nematodes, depending on the cultivated crop, makes it possible to assess the ecological and economic consequences of disturbed crop rotation, taking into account the conjuncture of the world food market. Climate change is another important challenge to be considered in the assessment of the nematode problem. Along with the noted increase in the bioclimatic potential of a number of agricultural lands in the Russian Federation, the development of the parasite during the growing season can occur not in three generations with a reduced fourth, but with a full cycle for the fourth generation.

Sublethal fluazaindolizine doses inhibit development of the cyst nematode Heterodera schachtii during sedentary parasitism.

Fluazaindolizine is a new compound for the control of plant-parasitic nematodes (PPNs) with an unknown and novel mode-of-action. This compound is very effective against important PPNs. However, investigations elucidating the impact of sublethal fluazaindolizine doses on early nematode virulence and plant-nematode interaction parameters are lacking. The effect of direct exposure of Heterodera schachtii juveniles to 50 ppm fluazaindolizine was negligible. Infection assays revealed a 57% reduction in adult females at 1.25 ppm and a 46% reduction in offspring at 40 ppm when juveniles were soaked in the compound for 48 h and subsequently inoculated onto Arabidopsis thaliana. Pre-incubation of A.thaliana roots with fluazaindolizine was not effective against H.schachtii. Conversely, supplementing the plant growth medium with fluazaindolizine led to a significant reduction of adults (-35%), females (-75%) and female size at 1.25 ppm and nearly completely inhibited nematode parasitism at 5 ppm. The impact of fluazaindolizine on A.thaliana was dependent on plant age, compound concentration and duration of contact. Very low sublethal fluazaindolizine concentrations, 5 or 10 ppm, did not interfere with nematode mobility, host finding, penetration, and induction of the feeding site, but specifically inhibited sedentary nematode development inside the root in a concentration-dependent manner. Fluazaindolizine does not have direct toxicity against PPN infective juveniles, but has a clear effect on nematodes during sedentary development. The formation of females and the development of offspring are strongly reduced. It will be interesting to identify the underlying mechanism in the future. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

New genetic tools for plant defense against parasitic nematodes

Нематоды относятся к числу значимых вредителей сельскохозяйственных растений. В обзоре рассмотрены последние данные о молекулярных механизмах устойчивости растений к цистообразующим и галловым нематодам, среди которых одни из наиболее вредоносных видов: Globodera rostochiensis, G. pallida, Heterodera schachtii, Meloidogyne chitwoodi и M. incognita. Например, золотистая картофельная нематода G. rostochiensis, зарегистрированная в 61 субъекте РФ на общей площади 1.8 млн га, способна приводить к потере от 19 до 90 % урожая картофеля. Биологические особенности нематод затрудняют разработку агротехнических способов борьбы с ними: цисты G. rostochiensis сохраняют жизнеспособность в почве в течение многих лет, нематициды токсичны или малоэффективны, поэтому предпочтительным методом борьбы с ними является интрогрессия генов устойчивости от родственных культурных и дикорастущих видов. Стратегия жизненного цикла цистообразующих и галловых нематод основана на способности личинок проникать в корни восприимчивых видов растений, репрограммировать клетки растения-хозяина, формирующие гигантские клетки или синцитии в качестве питающих структур, а также ингибировать иммунный ответ. Молекулярные механизмы, лежащие в основе такого взаимодействия в системе «патоген–хозяин», вызывают значительный интерес как с точки зрения управления морфогенезом растений, так и в аспекте разработки безопасных и эффективных способов борьбы с паразитическими нематодами. В обзоре рассмотрены данные об эффекторах, с помощью которых разные виды нематод контролируют иммунный ответ растения-хозяина, а также гены устойчивости (R-гены) и некоторые молекулярные механизмы, прерывающие формирование питающих структур и развитие паразита. Приведены новые данные о способах генетического контроля, основанных на одном из активно обсуждаемых в последнее время варианте механизма РНК-интерференции – HIGS (host induced gene silencing), представляющем собой адресное выключение экспрессии гена-мишени в клетках личинки нематоды с помощью специфических двуцепочечных РНК, синтезирующихся в клетках растения-хозяина. Индукция РНК-интерференции в клетках растений приводит к появлению молекул-медиаторов, способных инициировать аналогичный процесс в клетках фитофагов, взаимодействующих с растением, в том числе у личинок нематод. Описаны случаи, в которых такое адресное выключение экспрессии генов-мишеней приводило к нарушениям развития личинок и высокому уровню защиты сельскохозяйственных растений от наиболее опасных видов нематод.

Expression of a Fungal Lectin in Arabidopsis Enhances Plant Growth and Resistance Toward Microbial Pathogens and a Plant-Parasitic Nematode.

Coprinopsis cinerea lectin 2 (CCL2) is a fucoside-binding lectin from the basidiomycete C. cinerea that is toxic to the bacterivorous nematode Caenorhabditis elegans as well as animal-parasitic and fungivorous nematodes. We expressed CCL2 in Arabidopsis to assess its protective potential toward plant-parasitic nematodes. Our results demonstrate that expression of CCL2 enhances host resistance against the cyst nematode Heterodera schachtii. Surprisingly, CCL2-expressing plants were also more resistant to fungal pathogens including Botrytis cinerea, and the phytopathogenic bacterium Pseudomonas syringae. In addition, CCL2 expression positively affected plant growth indicating that CCL2 has the potential to improve two important agricultural parameters namely biomass production and general disease resistance. The mechanism of the CCL2-mediated enhancement of plant disease resistance depended on fucoside-binding by CCL2 as transgenic plants expressing a mutant version of CCL2 (Y92A), compromised in fucoside-binding, exhibited wild type (WT) disease susceptibility. The protective effect of CCL2 did not seem to be direct as the lectin showed no growth-inhibition toward B. cinerea in in vitro assays. We detected, however, a significantly enhanced transcriptional induction of plant defense genes in CCL2- but not CCL2-Y92A-expressing lines in response to infection with B. cinerea compared to WT plants. This study demonstrates a potential of fungal defense lectins in plant protection beyond their use as toxins.

Host plant penetration, development and life cycle of a Heterodera schachtii population from the Western Cape province, South Africa

Heterodera schachtii (Tylenchida: Heteroderidae), also called the sugar beet cyst nematode, are of economic importance worldwide. Oilseed rape (Brassica napus L.), which is a crop of global importance, suffers yield loss when it is infected with H. schachtii. The first report of the occurrence of H. schachtii in South Africa was made in 1968 on the Greater Cape Flats of the Western Cape province of South Africa, showing the widespread occurrence and the high nematode numbers on cabbage, cauliflower, beetroot and Brussels sprouts. The penetration, development and life cycle of a local H. schachtii population on seven vegetables (beetroot, broccoli, Brussels sprout, cabbage, cauliflower, lettuce and turnip) and three weeds (black nightshade, purslane and shepherd’s purse) commonly grown, or found, in the Greater Cape Flats region of the Western Cape, South Africa, and two candidate trap crops (white mustard and oilseed radish) were examined under laboratory conditions. All the vegetables and weeds were found to be good hosts of H. schachtii, with the exception of lettuce, which was found to be a non-host. Oilseed radish and white mustard allowed penetration and some nematode development, but no, or little, cyst formation. Female bodies filled with eggs were observed from 31 to 34 days after inoculation onwards on all the vegetables and weeds, except for on beetroot, on which female bodies filled with eggs were observed a few days later. The results from this study are important, especially in terms of the adaptation of vegetable crop rotation cycles that are practised on the Cape Flats, so as to prevent the build-up of H. schachtii populations in agricultural settings.