Ingestion of double-stranded RNA by preparasitic juvenile cyst nematodes leads to RNA interference

RNA interference is of value in determining gene function in many organisms. Plant parasitic nematodes are refractory to microinjection as a means of introducing RNA and do not show any oral uptake until they are within plants. We have used octopamine to stimulate uptake by preparasitic second stage juveniles of two cyst nematodes, Heterodera glycines and Globodera pallida. This new technique was used to facilitate uptake of double stranded RNA (dsRNA) together with fluoroscein isothiocyanate as a visual marker. Targeting cysteine proteinases did not reduce the number of parasites but caused a shift from the normal female/male ratio of 3:1 to 1:1 by 14 days postinfection (dpi). Exposure of H. glycines to dsRNA corresponding to a newly characterized protein with homology to C-type lectins did not affect sexual fate, but 41% fewer parasites were recovered from the plants. As expected, treatment with dsRNA corresponding to the major sperm protein (MSP) had no effect on either parasite development or sexual fate over 14 days. Northern analysis showed lower transcript abundance for the two targeted mRNAs that occur in J2, plus a later inhibition for MSP transcripts when males developed sperm at 15 dpi. These findings establish a procedure for RNAi of plant parasitic nematodes.

Engineered oryzacystatin-I expressed in transgenic hairy roots confers resistance to Globodera pallida

The cysteine proteinase inhibitor, oryzacystatin-I (Oc-I), and several engineered Oc-I variants have been tested for efficacy in inhibiting growth and development of both the free-living nematode, Caenorhabditis elegans, and the plant parasitic nematode Globodera pallida. To assist in the design of protein engineering experiments to improve the efficacy of Oc-I, an alignment of 28 cystatins and a molecular model of Oc-I were generated. Inhibitory activities (Ki) of wild-type and variant forms of Oc-I against both papain and the C. elegans cysteine proteinase, gcp-1, were measured. For one variant, in which residue Asp86 was deleted (Oc-I deltaD86), the Ki was reduced by 13- to 14-fold. LD50 studies to test the effect of Oc-I and Oc-I delta D86 against C. elegans showed the relative median potency of Oc-I delta D86 to be 0.76 that of wild-type Oc-I. When expressed in tomato hairy roots both Oc-I and Oc-I delta D86 had a detrimental effect on growth and development of G. pallida. This effect was significantly greater on Oc-I deltaD86-expressing roots leading to a reduction in size of G. pallida females to a level at which fecundity is profoundly affected.

Expression of the pea gene PSMTA in E. coli. Metal-binding properties of the expressed protein

The pea (Pisum sativum L.) gene PSMTA has an ORF encoding a predicted protein with sequence similarity to class I metallothioneins (MTS). To examine the metal-binding properties of the PSMTA protein it has been expressed in E. coli as a carboxyterminal extension of glutathione-S-transferase (GST). Metal ions were associated with the expressed protein when purified from lysates of E. coli grown in metal supplemented media. The pH of half-dissociation of Zn, Cd and Cu ions from the recombinant fusion protein was determined to be 5.35, 3.95 and 1.45 respectively, compared with equivalent estimates of 4.50, 3.00 and 1.80 for equine renal MT.

Resistance to both cyst and root-knot nematodes conferred by transgenic Arabidopsis expressing a modified plant cystatin

Plant nematodes are major pests of agriculture. Transgenic plant technology has been developed based on the use of proteinase inhibitors as nematode anti-feedants. The approach offers prospects for novel plant resistance and reduced use of environmentally damaging nematicides. A modified rice cystatin, Oc-I delta D86, expressed as a transgene in Arabidopsis thaliana, has a profound effect on the size and fecundity of females for both Heterodera schachtii (beet-cyst nematode) and Meloidogyne incognita (root-knot nematode). No females of either species achieved the minimum size they require for egg production. Ingestion of Oc-I delta D86 from the plant was correlated with loss of cysteine proteinase activity in the intestine thereby suppressing normal growth, as required of an effective antifeedant plant defence.

RNA interference in plant parasitic nematodes: a summary of the current status

SUMMARYRNA interference (RNAi) has emerged as an invaluable gene-silencing tool for functional analysis in a wide variety of organisms, particularly the free-living model nematode Caenorhabditis elegans. An increasing number of studies have now described its application to plant parasitic nematodes. Genes expressed in a range of cell types are silenced when nematodes take up double stranded RNA (dsRNA) or short interfering RNAs (siRNAs) that elicit a systemic RNAi response. Despite many successful reports, there is still poor understanding of the range of factors that influence optimal gene silencing. Recent in vitro studies have highlighted significant variations in the RNAi phenotype that can occur with different dsRNA concentrations, construct size and duration of soaking. Discrepancies in methodology thwart efforts to reliably compare the efficacy of RNAi between different nematodes or target tissues. Nevertheless, RNAi has become an established experimental tool for plant parasitic nematodes and also offers the prospect of being developed into a novel control strategy when delivered from transgenic plants.

Meloidogyne incognita: molecular and biochemical characterisation of a cathepsin L cysteine proteinase and the effect on parasitism following RNAi

RNA interference has been used to investigate the function of a cathepsin L cysteine proteinase Mi-cpl-1, in the plant-parasitic nematode Meloidogyne incognita. A reduction in gene transcript was observed and the number of nematodes infecting plants was reduced by almost 60% as was the number of established females producing eggs at 21 days post-infection. The cysteine proteinase activity of M. incognita, reported by the substrate GLUpNA, was inhibited by the cysteine proteinase inhibitor Oc-IDeltaD86. A reduction in cysteine proteinase activity was also seen following RNAi of Mi-cpl-1 in J2 stage nematodes. In situ hybridization analysis in young and mature female nematodes has shown that Mi-cpl-1 is expressed in the intestine, which suggests that its product is a digestive enzyme. The effects of knocking-out Mi-cpl-1gene function were consistent with a reduction in feeding efficiency. Here, we have shown a correlation between transcript abundance proteinase activity and parasitic success of M. incognita.

Enhanced transgenic plant resistance to nematodes by dual proteinase inhibitor constructs

Plant defence strategies usually involve the action of several gene products. Transgenic resistance strategies are likely to have enhanced efficacy when they involve more than one transgene. Here we explore possible mechanisms for the co-delivery of multiple effectors via a single transgene. As an example we report the co-delivery of two distinct proteinase inhibitors in Arabidopsis thaliana (L.) Heynh. to examine resistance against plant parasitic nematodes. A cysteine and serine proteinase inhibitor have been joined as translational fusions by one of two peptide linkers. One linker, part of the spacer region of a plant metallothionein-like protein (PsMTa), was selected to be cleaved in planta. A second linker, derived from the fungal enzyme galactose oxidase (GO) was chosen to be refractory to cleavage in planta. Western blot analysis of cell extracts confirmed the expected pattern of predominantly single inhibitors derived from the PsMTa construct and a primarily dual inhibitor from the GO construct. Analysis of cyst and root-knot nematodes recovered from transgenic Arabidopsis expressing inhibitors as single or dual molecules revealed the uptake of inhibitors with the exception of those linked by the PsMTa linker. This unexpected result may be due to residues of the PsMTa linker interacting with cell membranes. Despite lack of ingestion, PsMTa-linked cowpea trypsin inhibitor (CpTI) affected the sexual development of the cyst nematodes, indicating an external site of action. The engineered cystatin (Oc-I delta D86) component from the PsMTa constuct had no effect, indicating that ingestion is necessary for the cystatin to be effective. The delivery of dual inhibitors linked by the GO linker showed a clear additive effect over either inhibitor delivered singly. The application of this technology to other plant pathogens is discussed.

QPCR analysis and RNAi define pharyngeal gland cell-expressed genes of Heterodera glycines required for initial interactions with the host

Changes in transcript abundance of genes expressed in the three pharyngeal gland cells of Heterodera glycines after host invasion were monitored by quantitative polymerase chain reaction (qPCR) and the consequences of disrupting their expression studied by RNAi treatment prior to invasion. Two transcripts were known to be expressed in the two subventral gland cells (hg-pel and hg-eng-1), a further two in the single dorsal gland cell only (hg-gp and hg-syv46), and a fifth transcript (hg-cm) was expressed by both gland cell types. The qPCR study established that transcripts of hg-syv46 and hg-gp increased in abundance by 2 days postinfection (dpi), with the former remaining the most abundant. The hg-cm transcript level showed minor changes from 0 to 14 dpi but did fall by 21 dpi. In contrast, hg-eng-1 and hg-eng-2 messenger (m)RNA declined by 7 dpi and hg-pel by 14 dpi before it increased at 21 dpi. RNAi-targeting of hg-eng-1 reduced the number of females present on the plants at 10 days. Targeting of hg-gp, hg-cm, and hg-pel caused a change in sexual fate favoring male development on roots. Both effects were evident after targeting hg-syv46. Suppression of hg-eng-1 mRNA levels in second-stage juveniles (J2i) by RNAi was transient, with a recovery by 15 days of incubation in water after treatment. Presoaking H. glycines J2 with double-stranded RNA has value for studying gene function during the nematode's early interaction with a plant.

Characterization of intestinally active proteinases of cyst-nematodes

Cryostat sections of juvenile and adult female stages of the soybean cyst-nematode, Heterodera glycines, were incubated with 4 different naphthylamide-linked peptide substrates to localize and characterize proteinase activity within the animal. Detected activity was restricted to the intestine and 2 distinct classes of proteinase were identified on the basis of substrate specificity and sensitivity to plant proteinase inhibitors. A cathepsin L-like cysteine proteinase activity capable of hydrolysing the synthetic substrates Z-Ala-Arg-Arg-MNA and Z-Phe-Arg-MNA but not Z-Arg-Arg-MNA or L-Arg-NA was inhibited by an engineered variant of a cysteine proteinase inhibitor from rice (Oc-I delta D86). The cleavage of Z-Phe-Arg-MNA was sensitive to inhibition by a combination of Oc-I delta D86 and cowpea trypsin inhibitor (CpTI). Degenerate oligonucleotide primers were used to amplify fragments of cysteine proteinase genes from 2 cyst-nematodes, H. glycines and Globodera pallida. Comparison of the H. glycines fragment with known genes established highest homology to cathepsin L-like genes. In contrast, the amplified G. pallida fragment displayed greatest homology to cathepsin B-like genes from Caenorhabditis elegans.

Continual green-fluorescent protein monitoring of cauliflower mosaic virus 35S promoter activity in nematode-induced feeding cells in Arabidopsis thaliana

The responsiveness of the cauliflower mosaic virus 35S promoter in feeding sites developed by both sexes of Heterodera schachtii and female Meloidogyne incognita has been studied. The objective was to establish the value of green-fluorescent protein (GFP) as a nondestructive reporter gene system for characterizing promoter activity at nematode feeding sites in vivo. Growth units were devised that allowed individual feeding sites in roots of Arabidopsis thaliana to be observed by both bright-field and epifluorescent illumination. Changes in GFP expression were visually observed under experimental conditions that resulted in chloroplast formation in syncytia but not other root cells. Changes in GFP levels altered the extent of quenching, by this protein, of red light emitted by chlorophyll within the chloroplasts under violet excitation. Image analysis provided a semiquantitative basis for simultaneous measurement of changes in GFP fluorescence and the unquenched emission by chlorophyll. GFP levels were constant in cells surrounding the syncytium induced by H. schachtii, but they fell progressive from 10 to 35 days postinfection within this structure. Significant reduction in GFP levels was not limited to the early part of the time course but also occurred between 27 and 35 days postinfection. GFP was detected by immunoblotting in females of M. incognita but not in H. schachtii parasitizing similar GFP-expressing roots.

Characterisation by RNAi of pioneer genes expressed in the dorsal pharyngeal gland cell of Heterodera glycines and the effects of combinatorial RNAi

Changes in transcript abundance of 24 genes expressed in the dorsal pharyngeal gland cell of Heterodera glycines encoding for putative secretions of unknown function were monitored by quantitative PCR (qPCR) at 0, 2, 7, 14 and 21 days post-invasion (pi) of soybean plantlets. Five groups of temporal patterns (A, B1, B2, C and D) were defined for the 24 genes plus data for two previously studied genes expressed in the same cell. Group D (two genes) showed no significant increase between 0 and 2 days pi and were the least abundantly expressed at 7-21 days pi. Transcripts of group C (nine genes including one studied previously) increased in abundance from 0 to 2 days pi but were the second least expressed for 7-21 days pi. Groups A (three genes), B1 (seven genes) and B2 (five genes including one studied previously) were all abundant at 7-21 days pi. B1 and B2 were discriminated by their relative abundance at 0 and 2 days pi. RNA interference (RNAi) targeting two genes of group A and one each of B1 and B2 in nematodes prior to invasion resulted in phenotypic effects on total parasites per plant and sexual fate at 10 days pi. Phenotype penetrance was reduced for three genes showing such effects and one with a strong effect in earlier work when two genes rather than one were concurrently targeted for RNAi. One gene (dg13) was more abundantly expressed after combinatorial RNAi than for either control nematodes or when targeting singly by RNAi. This work reports the unexpected elevation in mRNA expression after combinatorial RNAi that requires understanding before combinatorial RNAi can be advanced for highly effective cyst nematode control via plant biotechnology.

Transgenic Arabidopsis leaf tissue expressing a modified oryzacystatin shows resistance to the field slug Deroceras reticulatum (Müller)

Transgenic Arabidopsis thaliana has been developed which expresses the oryzacystatin mutant OC-I delta 86, which is an inhibitor of the major proteinase present in the digestive gland of the slug, Deroceras reticulatum. When fed on leaf tissue from plants expressing this inhibitor the growth of juvenile slugs was significantly reduced by 31% compared with those feeding on control leaf tissue. Furthermore, while surviving slugs did not individually consume less when feeding on leaf tissue expressing OC-I delta 86, the total amount of leaf tissue eaten was 50% less, due to reduced survival of slugs. The synthetic cysteine proteinase inhibitors E-64 and leupeptin also significantly reduced slug weight gain (by at least 40%) and digestive gland cysteine proteinase activity when administered in an artificial diet, indicating that their antimetabolic effects are due to direct inhibition of gut proteolytic activity. These results suggest that transgenic crop plants expressing phytocystatins could be used to suppress the growth rates of slug populations in the field.

Characterization of cDNAs encoding serine proteinases from the soybean cyst nematode Heterodera glycines

Three cDNAs encoding serine proteinases (HGSPI-III) were isolated from a cDNA library constructed from feeding females of Heterodera glycines. The library was screened with three separate serine proteinase gene fragments amplified from cDNA of H. glycines using consensus oligonucleotide primers. Each predicted protein contains a secretion signal sequence, a propeptide and a mature protein of 226-296 amino acids. One of the predicted enzymes, HGSP-II has 41% identity to a chymotrypsin-like enzyme from the mollusc, Haliotis rufescens, and analysis of key residues involved in substrate binding also suggests a chymotrypsin-like specificity. HGSP-I and HGSP-III show greatest homology to kallikreins but sequence analysis does not allow prediction of their substrate preferences. Southern blot analysis suggests that HGSP-II and HGSP-III are encoded by single-copy genes in contrast to HGSP-I which may have two or more homologues. The regions encoding the mature proteinases were cloned into an expression vector and recombinant protein produced in Escherichia coli. Both HGSP-I and HGSP-II were shown, after refolding, to cleave the synthetic peptide N-CBZ-Phe-Arg-7-amido-4-methylcoumarin, and this activity could be inhibited by the cowpea trypsin inhibitor, CpTI. HGSP-III showed no activity against the synthetic substrates tested. The information gained from these studies indicates that serine proteinases are an important group of enzymes in H. glycines and further characterization will aid the development of a proteinase inhibitor-based approach for transgenic plant resistance to plant parasitic nematodes.

Parasitic nematodes, proteinases and transgenic plants

Parasite proteinases have important functions in host-parasite interactions. Consequently, they have been investigated as targets for the control of both plant and animal parasites. Plant parasitic nematodes cause estimated annual losses to world agriculture of US$100 billion and, currently, their control often relies on highly toxic nematicides, with associated environmental risks. The potential of disrupting digestive proteinases for plant parasitic nematode control, via expression of proteinase inhibitors in transgenic plants, is summarized here by Catherine Lilley, Pauline Devlin, Peter Urwin and Howard Atkinson. They then consider whether the approach of expressing antinematode proteins in plants can be adapted for control of certain animal parasitic nematodes.

Plant-parasitic nematodes respond to root exudate signals with host-specific gene expression patterns

Plant parasitic nematodes must be able to locate and feed from their host in order to survive. Here we show that Pratylenchus coffeae regulates the expression of selected cell-wall degrading enzyme genes relative to the abundance of substrate in root exudates, thereby tailoring gene expression for root entry of the immediate host. The concentration of cellulose or xylan within the exudate determined the level of β-1,4-endoglucanase (Pc-eng-1) and β-1,4-endoxylanase (Pc-xyl) upregulation respectively. Treatment of P. coffeae with cellulose or xylan or with root exudates deficient in cellulose or xylan conferred a specific gene expression response of Pc-eng-1 or Pc-xyl respectively with no effect on expression of another cell wall degrading enzyme gene, a pectate lyase (Pc-pel). RNA interference confirmed the importance of regulating these genes as lowered transcript levels reduced root penetration by the nematode. Gene expression in this plant parasitic nematode is therefore influenced, in a host-specific manner, by cell wall components that are either secreted by the plant or released by degradation of root tissue. Transcriptional plasticity may have evolved as an adaptation for host recognition and increased root invasion by this polyphagous species.

Plant parasitic nematodes feed from plant roots to support their development. In order to enter and reproduce within the host the nematode must interact with the components exuded by the root. The components are known to vary between individual plant species thus presenting different challenges for the nematode. We observe upregulation of two cell wall degrading enzyme genes in Pratylenchus coffeae upon exposure to root exudates. The nematode genes are differentially expressed dependent upon the identity of the plant. The relative expression of each gene correlates with the abundance of the encoded enzyme substrate in the nematode environment, indicating that the nematode perceives these components and responds by tailoring gene expression for what is currently required for host-parasitism. This ability may explain the wide host range of this nematode species and may be shared by other parasites.

Syncytia formed by adult female Heterodera schachtii in Arabidopsis thaliana roots have a distinct cell wall molecular architecture

• Plant-parasitic cyst nematodes form a feeding site, termed a syncytium, through which the nematode obtains nutrients from the host plant to support nematode development. The structural features of cell walls of syncytial cells have yet to be elucidated. • Monoclonal antibodies to defined glycans and a cellulose-binding module were used to determine the cell wall architectures of syncytial and surrounding cells in the roots of Arabidopsis thaliana infected with the cyst nematode Heterodera schachtii. • Fluorescence imaging revealed that the cell walls of syncytia contain cellulose and the hemicelluloses xyloglucan and heteromannan. Heavily methyl-esterified pectic homogalacturonan and arabinan are abundant in syncytial cell walls; galactan could not be detected. This is suggestive of highly flexible syncytial cell walls. • This work provides important information on the structural architecture of the cell walls of this novel cell type and reveals factors that enable the feeding site to perform its functional requirements to support nematode development.

Involvement of the NH2-terminal region of oryzacystatin-I in cysteine proteinase inhibition

Cystatins are small protein inhibitors of cysteine proteinases. The relative importance of the N-terminal region of cystatins, and of a conserved glycine within this region, remains unclear despite several studies. It was found that deletion of the N-terminal 21 amino acids abolishes the inhibitory capacity of oryzacystatin-I. The importance of a conserved glycine residue (Gly10) was also examined by replacing it with 11 other amino acids. Three further glycine residues (Gly5, -6 and -11) in this N-terminal region of oryzacystatin-I were similarly mutated. Only those variants in which Gly10 was substituted show any significant change in inhibitory capacity compared with wild-type oryzacystatin-I. The inhibitory characteristics of hybrid cystatin molecules comprising regions of chicken egg white cystatin and oryzacystatin were also examined. It is suggested that in common with animal cystatins, the N-terminal region of the plant cystatin, oryzacystatin-I, and in particular the highly conserved Gly10 residue are important for effective inhibition of papain.

Characterization of plant nematode genes: identifying targets for a transgenic defence

Current control of plant parasitic nematodes often relies on highly toxic and environmentally harmful nematicides. As their use becomes increasingly restricted there is an urgent need to develop crop varieties with resistance to nematodes. The limitations surrounding conventional plant breeding ensure there is a clear opportunity for transgenic resistance to lessen current dependence on chemical control. The increasing use of molecular biology techniques in the field of plant nematology is now providing useful information for the design of novel defences to meet the new needs. Plant responses to parasitism are being investigated at the molecular level and nematode gene products that could be targets for a direct anti-nematode defence are being characterized. The potential of an anti-feedant approach to nematode control has been demonstrated. It is based on the transgenic expression of proteinase inhibitors. The rational development of this strategy involves characterization of nematode proteinase genes and optimization of inhibitors by protein engineering. Durability of the resistance can be enhanced by stacking transgenes directed at different nematode targets.

Disruption of carbon for nutrient exchange between potato and arbuscular mycorrhizal fungi enhanced cyst nematode fitness and host pest tolerance

Plants simultaneously interact with a range of biotrophic symbionts, ranging from mutualists such as arbuscular mycorrhizal fungi (AMF), to parasites such as the potato cyst nematode (PCN). The exchange of mycorrhizal-acquired nutrients for plant-fixed carbon (C) is well studied; however, the impact of competing symbionts remains underexplored. In this study, we examined mycorrhizal nutrient and host resource allocation in potato with and without AMF and PCN using radioisotope tracing, whilst determining the consequences of such allocation. The presence of PCN disrupted C for nutrient exchange between plants and AMF, with plant C overwhelmingly obtained by the nematodes. Despite this, AMF maintained transfer of nutrients on PCN-infected potato, ultimately losing out in their C for nutrient exchange with the host. Whilst PCN exploited the greater nutrient reserves to drive population growth on AMF-potato, the fungus imparted tolerance to allow the host to bear the parasitic burden. Our findings provide important insights into the belowground dynamics of plant-AMF symbioses, where simultaneous nutritional and nonnutritional benefits conferred by AMF to hosts and their parasites are seldom considered in plant community dynamics. Our findings suggest this may be a critical oversight, particularly in the consideration of C and nutrient flows in plant and soil communities.

GUS expression in Arabidopsis directed by 5' regions of the pea metallothionein-like gene PsMTA

Upstream sequences (including the first seven codons) of a metallothionein (MT)-like gene from pea, PsMTA, were fused to GUS and introduced into Arabidopsis. High-level GUS expression was detected in the roots of plants grown on MS medium, except in regions proximal to the root apex. There was precise delineation of the root-shoot boundary. In soil-grown plants there was low GUS expression and this was absent from the more mature regions of the roots. In the aerial tissues of soil-grown plants, GUS expression was restricted to hydathodes, stipules, expanding cotyledons and the following senescent tissues: leaves, cotyledons, petals, sepals, filaments, stigmas, nectaries and siliques. A 298 bp region was shown to be required for GUS expression in roots but not for expression in vegetative aerial tissues of plants grown on MS medium. This region contains predicted ethylene-responsive elements (EREs) but similar patterns of GUS expression were detected in etr1 seedlings. GUS expression was significantly higher in roots exposed to 500 nM copper, but this increase was small in proportion to expression in roots exposed to 50 nM copper.

Constant Isothiocyanate-Release Potentials across Biofumigant Seeding Rates

Biofumigation is an integrated pest-management method involving the mulching of a glucosinolate-containing cover crop into a field in order to generate toxic isothiocyanates (ITCs), which are effective soil-borne-pest-control compounds. Variation in biofumigation efficacy demonstrates a need to better understand the factors affecting pest-control outcomes and develop best practices for choosing biofumigants, growth conditions, and mulching methods that allow the greatest potential isothiocyanate release. We measured the glucosinolate concentrations of six different commercial varieties of three biofumigant plant species: Brassica juncea (ISCI99, Vitasso, and Scala) Raphanus sativus (Diablo and Bento), and Sinapis alba (Ida Gold). The plants were grown in the range of commercially appropriate seeding rates and sampled at three growth stages (early development, mature, and 50% flowering). Within biofumigant species, the highest ITC-release potentials were achieved with B. juncea cv. ISCI99 and R. sativus cv. Bento. The highest ITC-release potential occurred at the 50% flowering growth stage across the species. The seeding rate had a minor impact on the ITC-release potential of R. sativus but had no significant effects on the ITC-release potentials of the B. juncea or S. alba cultivars.

A High-Throughput Molecular Pipeline Reveals the Diversity in Prevalence and Abundance of Pratylenchus and Meloidogyne Species in Coffee Plantations

Coffee yields are adversely affected by plant-parasitic nematodes and the pathogens are largely underreported because a simple and reliable identification method is not available. We describe a polymerase chain reaction-based approach to rapidly detect and quantify the major Pratylenchus and Meloidogyne nematode species that are capable of parasitizing coffee. The procedure was applied to soil samples obtained from a number of coffee farms in Brazil, Vietnam, and Indonesia to assess the prevalence of these species associated both with coffee (Coffea arabica and C. canephora) and its intercropped species Musa acuminata (banana) and Piper nigrum (black pepper). Pratylenchus coffeae and P. brachyurus were associated with coffee in all three countries but there were distinct profiles of Meloidogyne spp. Meloidogyne incognita, M. exigua, and M. paranaensis were identified in samples from Brazil and M. incognita and M. hapla were detected around the roots of coffee in Vietnam. No Meloidogyne spp. were detected in samples from Indonesia. There was a high abundance of Meloidogyne spp. in soil samples in which Pratylenchus spp. were low or not detected, suggesting that the success of one genus may deter another. Meloidogyne spp. in Vietnam and Pratylenchus spp. in Indonesia were more numerous around intercropped plants than in association with coffee. The data suggest a widespread but differential nematode problem associated with coffee production across the regions studied. The issue is compounded by the current choice of intercrops that support large nematode populations. Wider application of the approach would elucidate the true global scale of the nematode problem and the cost to coffee production. [Formula: see text] Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Characterization of two cDNAs encoding cysteine proteinases from the soybean cyst nematode Heterodera glycines

Two cDNAs encoding cysteine proteinases were isolated from a cDNA library constructed from feeding females of Heterodera glycines. The library was screened with a cysteine proteinase gene fragment originally amplified from cDNA of H. glycines. Database searches predict that 1 cDNA (hgcp-I) encodes a cathepsin L-like proteinase, while the second (hgcp-II) encodes a cathepsin S-like enzyme. Both predicted proteins contain a short secretion signal sequence, a long propeptide and a mature protein of 219 amino acids. Southern blot analysis suggests that the cathepsin S-like enzyme, HGCP-II, is encoded by a single-copy gene in contrast to the cathepsin L-like proteinase, HGCP-I which may have 2 homologues. The regions encoding the mature proteinases were cloned into an expression vector and recombinant protein produced in E. coli. HGCP-I was shown, after refolding, to cleave the synthetic peptide Z-Phe-Arg-AMC, and this activity could be inhibited by the engineered rice cystatin Oc-I delta D86. HGCP-II showed no activity against the synthetic substrates tested. The knowledge gained from these studies will improve our understanding of plant nematode proteinases and aid the development of a rational proteinase inhibitor-based approach to plant nematode resistance.

Image Analysis of the Growth of Globodera pallida and Meloidogyne incognita on Transgenic Tomato Roots Expressing Cystatins

An approach based on image analysis that enables rapid collection and analysis of nematode size and shape during growth is reported. This technique has been applied to assess Meloidogyne incognita and Globodera pallida during their development over 35 and 42 days, respectively, on transgenic tomato roots expressing the wild-type rice cystatin Oc-I or an engineered variant, Oc-IAD86. Morphometric values were established that subdivided enlarged saccate females from other life stages. Analysis of this data subset indicates that the size of females and the frequency with which they parasitize roots expressing a cystatin are reduced. Results also demonstrate that cystatins can influence the growth of G. pallida prior to the adult stage. Similar image analysis procedures should be generally applicable to the study of host status or erivironmental factors that influence growth rates of plant-parasitic nematodes.