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

WOX11-mediated cell size control in Arabidopsis attenuates growth and fecundity of endoparasitic cyst nematodes

Cyst nematodes establish permanent feeding structures called syncytia inside the host root vasculature, disrupting the flow of water and minerals. In response, plants form WOX11-mediated adventitious lateral roots at nematode infection sites. WOX11 adventitious lateral rooting modulates tolerance to nematode infections; however, whether this also benefits nematode parasitism remains unknown. Here, we report on bioassays using a 35S::WOX11-SRDX transcriptional repressor mutant to investigate whether WOX11 adventitious lateral rooting promotes syncytium development and thereby female growth and fecundity. Moreover, we chemically inhibited cellulose biosynthesis to verify if WOX11 directly modulates cell wall plasticity in syncytia. Finally, we performed histochemical analyses to test if WOX11 mediates syncytial cell wall plasticity via reactive oxygen species (ROS). Repression of WOX11-mediated transcription specifically enhanced the radial expansion of syncytial elements, increasing both syncytium size and female offspring. The enhanced syncytial hypertrophy observed in the 35S::WOX11-SRDX mutant could be phenocopied by chemical inhibition of cellulose biosynthesis and was associated with elevated levels of ROS at nematode infection sites. We, therefore, conclude that WOX11 restricts radial expansion of nematode-feeding structures and female growth and fecundity, likely by modulating ROS-mediated cell wall plasticity mechanisms. Remarkably, this novel role of WOX11 in plant cell size control is distinct from WOX11 adventitious lateral rooting underlying disease tolerance.

A nematode-inducible promoter can effectively drives RNAi construct to confer Meloidogyne incognita resistance in tomato

KEY MESSAGE

Heterologous expression of a nematode-responsive promoter in tomato successfully driven the RNAi constructs to impart root-knot nematode resistance. The root-knot nematode Meloidogyne incognita seriously afflicts the global productivity of tomatoes. Nematode management options are extremely reliant on chemical methods, however, only a handful of nematicides are commercially available. Additionally, nematodes have developed resistance-breaking phenotypes against the commercially available Mi gene-expressing tomatoes. Nematode resistance in crop plants can be enhanced using the bio-safe RNAi technology, in which plants are genetically modified to express nematode gene-specific dsRNA/siRNA molecules. However, the majority of the RNAi crops conferring nematode tolerance have used constitutive promoters, which have many limitations. In the present study, using promoter-GUS fusion, we functionally validated two nematode-inducible root-specific promoters (pAt1g74770 and pAt2g18140, identified from Arabidopsis thaliana) in the Solanum lycopersicum-M. incognita pathosystem. pAt2g18140 was found to be nematode-responsive during 10-21 days post-inoculation (dpi) and became non-responsive during the late infection stage (28 dpi). In contrast, pAt1g74770 remained nematode-responsive for a longer duration (10-28 dpi). Next, a number of transgenic lines were developed that expressed RNAi constructs (independently targeting the M. incognita integrase and splicing factor genes) driven by the pAt1g74770 promoter. M. incognita parasitic success (measured by multiplication factor ratio) in pAt1g74770:integrase and pAt1g74770:splicing factor RNAi lines were significantly reduced by 60.83-74.93% and 69.34-75.31%, respectively, compared to the control. These data were comparable with the RNAi lines having CaMV35S as the promoter. Further, a long-term RNAi effect was evident, because females extracted from transgenic lines were of deformed shape with depleted transcripts of integrase and splicing factor genes. We conclude that pAt1g74770 can be an attractive alternative to drive localized expression of RNAi constructs rather than using a constitutive promoter. The pAt1g74770-driven gene silencing system can be expanded into different plant-nematode interaction models.

Carboxypeptidase inhibitors from Solanaceae as a new subclass of pathogenesis related peptide aiming biotechnological targets for plant defense

Background: Plant protease inhibitors play a crucial role in inhibiting proteases produced by phytopathogens and exhibiting inhibitory effects on nematodes, fungi, and insects, making them promising candidates for crop protection. Specifically, carboxypeptidase inhibitors, a subset of proteinase inhibitors, have been extensively studied in potato and tomato of Solanaceae plant family. However, further research is needed to fully understand the functions and biotechnological potential of those inhibitors in plants. This work aimed to in silico characterize carboxypeptidase inhibitors from Solanaceae as potential antimicrobial and defense agents focused on biotechnological targets. Methods: The methodology employed involved search in UniProt, PDB, KNOTTIN, NCBI, and MEROPS databases for solanaceous carboxypeptidase inhibitors, phylogenetic relationships and conservation patterns analyzes using MEGA-X software and Clustal Omega/MView tools, physicochemical properties and antimicrobial potential prediction using ProtParam, ToxinPred, iAMPred, and APD3 tools, and structural features prediction using PSIPRED. Results and discussion: A systematic literature search was conducted to identify relevant studies on Solanaceae carboxypeptidase inhibitors and their activities against pathogens. The selected studies were reviewed and the main findings compiled. The characterization of Solanaceae carboxypeptidase inhibitors proposed for the first time the global sequence consensus motif CXXXCXXXXDCXXXXXCXXC, shedding light on carboxypeptidase inhibitors distribution, sequence variability, and conservation patterns. Phylogenetic analysis showed evolutionary relationships within the Solanaceae family, particularly in Capsicum, Nicotiana, and Solanum genera. Physicochemical characteristics of those peptides indicated their similarity to antimicrobial peptides. Predicted secondary structures exhibited variations, suggesting a broad spectrum of action, and studies had been demonstrated their activities against various pathogens. Conclusion: Carboxypeptidase inhibitors are being proposed here as a new subclass of PR-6 pathogenesis-related proteins, which will aid in a focused understanding of their functional roles in plant defense mechanisms. These findings confirm the Solanaceae carboxypeptidase inhibitors potential as defense agents and highlight opportunities for their biotechnological applications in pathogen control.

Field test of Easter lilies transformed with a rice cystatin gene for root lesion nematode resistance

Easter lilies, Lilium longiflorum cv. Nellie White are a staple of the floral industry. In the U.S. most of the Easter lilies are grown in Oregon and California along the coast where there is a micro climate that is favorable to growth of lilies. The main pest when growing lilies in the field is Pratylenchus penetrans, the root lesion nematode. Easter lilies are one of the most expensive crops to produce because of the cost of chemicals used to control P. penetrans and other pathogens that infect the lilies. Our previous study had shown that transgenic Easter lilies containing a rice cystatin gene (Oc-IΔD86 that has a deleted Asp86) were resistant to P. penetrans in vitro. This study examined growth characteristics of five independently transformed lines of the cystatin Easter lilies compared to non-transformed Nellie White for three seasons in the field in Brookings, Oregon. Liles grown in three soil chemical treatments 1) preplant fumigation, 2) preplant fumigation plus at plant organophosphate, and 3) at plant organophosphate were compared to those grown in nontreated soil. Growth characteristics evaluated included: time of shoot emergence, survival of plants, size of plants, visual ratings of plant health, basal roots and stem roots, weight of foliage and roots, and number and size of bulblets that developed on stems. Nematodes were counted following their extraction from the roots. While not totally resistant, when planted in the field, transformed lines demonstrated and maintained a degree of resistance to lesion nematode over two growing seasons and displayed desirable growth and quality characteristics similar to non-transformed lilies.

Gall-specific promoter, an alternative to the constitutive CaMV35S promoter, drives host-derived RNA interference targeting Mi-msp2 gene to confer effective nematode resistance

One of the major obligate plant parasites causing massive economic crop losses belongs to the class of root-knot nematodes (RKNs). Targeting of major nematode parasitism genes via Host Delivered-RNAi (HD-RNAi) to confer silencing is established as one of the most effective approaches to curb nematode infection. Utilizing nematode-responsive root-specific (NRRS) promoters to design a dsRNA molecule targeting approach to hamper nematode parasitism. Here, a previously validated peroxidase gall specific promoter, pAt2g18140, from Arabidopsis was employed to express the dsRNA construct of the nematode effector gene Mi-msp2 from Meloidogyne incognita. Arabidopsis RNAi lines of CaMV35S::Mi-msp2-RNAi and pAt2g18140::Mi-msp2-RNAi were compared with control plants to assess the decrease in plant nematode infection. When subjected to infection, the maximum reductions in the numbers of galls, females and egg masses in the CaMV35S::Mi-msp2-RNAi lines were 61%, 66% and 95%, respectively, whereas for the pAt2g18140::Mi-msp2-RNAi lines, they were 63%, 68% and 100%, respectively. The reduction in transcript level ranged from 79%-82% for CaMV35S::Mi-msp2-RNAi and 72%-79% for the pAt2g18140::Mi-msp2-RNAi lines. Additionally, a reduction in female size and a subsequent reduction in next-generation fecundity demonstrate the efficacy and potential of the gall specific promoter pAt2g18140 for utilization in the development of HD-RNAi constructs against RKN, as an excellent alternative to the CaMV35S promoter.

Meloidogyne enterolobii, a Major Threat to Tomato Production: Current Status and Future Prospects for Its Management

The guava root-knot nematode, Meloidogyne enterolobii (Syn. M. mayaguensis), is an emerging pathogen to many crops in the world. This nematode can cause chlorosis, stunting, and reduce yields associated with the induction of many root galls on host plants. Recently, this pathogen has been considered as a global threat for tomato (Solanum lycopersicum L.) production due to the lack of known resistance in commercially accepted varieties and the aggressiveness of M. enterolobii. Both conventional morphological and molecular approaches have been used to identify M. enterolobii, an important first step in an integrated management. To combat root-knot nematodes, integrated disease management strategies such as crop rotation, field sanitation, biocontrol agents, fumigants, and resistant cultivars have been developed and successfully used in the past. However, the resistance in tomato varieties mediated by known Mi-genes does not control M. enterolobii. Here, we review the current knowledge on geographic distribution, host range, population biology, control measures, and proposed future strategies to improve M. enterolobii control in tomato.

Identification and characterisation of serotonin signalling in the potato cyst nematode Globodera pallida reveals new targets for crop protection

Plant parasitic nematodes are microscopic pathogens that invade plant roots and cause extensive damage to crops. We have used a chemical biology approach to define mechanisms underpinning their parasitic behaviour: We discovered that reserpine, a plant alkaloid that inhibits the vesicular monoamine transporter (VMAT), potently impairs the ability of the potato cyst nematode Globodera pallida to enter the host plant root. We show this is due to an inhibition of serotonergic signalling that is essential for activation of the stylet which is used to access the host root. Prompted by this we identified core molecular components of G. pallida serotonin signalling encompassing the target of reserpine, VMAT; the synthetic enzyme for serotonin, tryptophan hydroxylase; the G protein coupled receptor SER-7 and the serotonin-gated chloride channel MOD-1. We cloned each of these molecular components and confirmed their functional identity by complementation of the corresponding C. elegans mutant thus mapping out serotonergic signalling in G. pallida. Complementary approaches testing the effect of chemical inhibitors of each of these signalling elements on discrete sub-behaviours required for parasitism and root invasion reinforce the critical role of serotonin. Thus, targeting the serotonin signalling pathway presents a promising new route to control plant parasitic nematodes.

Legumes Protease Inhibitors as Biopesticides and Their Defense Mechanisms against Biotic Factors

Legumes are affected by biotic factors such as insects, molds, bacteria, and viruses. These plants can produce many different molecules in response to the attack of phytopathogens. Protease inhibitors (PIs) are proteins produced by legumes that inhibit the protease activity of phytopathogens. PIs are known to reduce nutrient availability, which diminishes pathogen growth and can lead to the death of the pathogen. PIs are classified according to the specificity of the mechanistic activity of the proteolytic enzymes, with serine and cysteine protease inhibitors being studied the most. Previous investigations have reported the efficacy of these highly stable proteins against diverse biotic factors and the concomitant protective effects in crops, representing a possible replacement of toxic agrochemicals that harm the environment.

Genome-Wide Identification and Expression Analysis of the Protease Inhibitor Gene Families in Tomato

The protease inhibitors (PIs) in plants are involved primarily in defense against pathogens and pests and in response to abiotic stresses. However, information about the PI gene families in tomato (Solanumlycopersicum), one of the most important model plant for crop species, is limited. In this study, in silico analysis identified 55 PI genes and their conserved domains, phylogenetic relationships, and chromosome locations were characterized. According to genetic structure and evolutionary relationships, the PI gene families were divided into seven families. Genome-wide microarray transcription analysis indicated that the expression of SlPI genes can be induced by abiotic (heat, drought, and salt) and biotic (Botrytiscinerea and tomato spotted wilt virus (TSWV)) stresses. In addition, expression analysis using RNA-seq in various tissues and developmental stages revealed that some SlPI genes were highly or preferentially expressed, showing tissue- and developmental stage-specific expression profiles. The expressions of four representative SlPI genes in response to abscisic acid (ABA), salicylic acid (SA), ethylene (Eth), gibberellic acid (GA). and methyl viologen (MV) were determined. Our findings indicated that PI genes may mediate the response of tomato plants to environmental stresses to balance hormone signals. The data obtained here will improve the understanding of the potential function of PI gene and lay a foundation for tomato breeding and transgenic resistance to stresses.

Tomato Natural Resistance Genes in Controlling the Root-Knot Nematode

The root-knot nematode (RKN) is one of the most dangerous and widespread types of nematodes affecting tomatoes. There are few methods for controlling nematodes in tomatoes. Nature resistance genes (R-genes) are important in conferring resistance against nematodes. These genes that confer resistance to the RKN have already been identified as Mi-1, Mi-2, Mi-3, Mi-4, Mi-5, Mi-6, Mi-7, Mi-8, Mi-9, and Mi-HT. Only five of these genes have been mapped. The major problem is that their resistance breaks down at high temperatures. Some of these genes still work at high temperatures. In this paper, the mechanism and characteristics of these natural resistance genes are summarized. Other difficulties in using these genes in the resistance and how to improve them are also mentioned.

The protein elicitor Hrip1 enhances resistance to insects and early bolting and flowering in Arabidopsis thaliana

The elicitor Hrip1 isolated from necrotrophic fungus Alternaria tenuissima, could induce systemic acquired resistance in tobacco to enhance resistance to tobacco mosaic virus. In the present study, we found that the transgenic lines of Hrip1-overexpression in wild type (WT) Arabidopsis thaliana were more resistant to Spodoptera exigua and were early bolting and flowering than the WT. A profiling of transcription assay using digital gene expression profiling was used for transgenic and WT Arabidopsis thaliana. Differentially expressed genes including 40 upregulated and three downregulated genes were identified. In transgenic lines of Hrip1-overexpression, three genes related to jasmonate (JA) biosynthesis were significantly upregulated, and the JA level was found to be higher than WT. Two GDSL family members (GLIP1 and GLIP4) and pathogen-related gene, which participated in pathogen defense action, were upregulated in the transgenic line of Hrip1-overexpression. Thus, Hrip1 is involved in affecting the flower bolting time and regulating endogenous JA biosynthesis and regulatory network to enhance resistance to insect.

Remusatia vivipara lectin and Sclerotium rolfsii lectin interfere with the development and gall formation activity of Meloidogyne incognita in transgenic tomato

Root knot nematodes are serious threats to growth and yield of solaneous crops including tomato. In this study, a binary vector carrying Remusatia vivipara (rvl1) and Sclerotium rolfsii (srl1) lectin genes were introduced independently into Lycopersicon esculentum cv. Pusa Ruby via Agrobacterium tumefaciens for resistance against root knot nematode, Meloidogyne incognita. In total, one hundred and one rvl1 and srl1-transformed plants exhibiting kanamycin resistance were confirmed to carry transgenes as detected by polymerase chain reaction (PCR) with 4.59% transformation efficiency. Genetic analysis of T₁ progeny confirmed Mendelian segregation of the introduced genes. Three events each of rvl1 and srl1 transgenic tomato were randomly selected for further confirmation by Southern and TAIL-PCR analyses. All three events of srl1 transgenics showed single copy transgene, whereas two rvl1 transgenic events showed single copy of transgene, while remaining event showed two copies of transgenes. Site of integration obtained for rvl1 and srl1 transgenic events by TAIL-PCR revealed that all the three events of rvl1 and srl1 transgenics differed for their site of integration and insertion sites did not contain any predicted gene. Moreover, expression of the rvl1 and srl1 transgenes was detected by haemagglutination assay in all three events of rvl1 and srl1, but not in non-transgenic tomato plant. Homozygous progenies of these events were grown and inoculated with M. incognita. Development and reproduction of M. incognita was severely affected in transgenic tomato plants expressing RVL1 and SRL1 exhibiting the high levels of resistance compared to non-transgenic plants. Therefore, these transgenic lines demonstrate a promising potential for variety development of tomato lines with enhanced resistance against M. incognita.

RNAi for Resistance Against Biotic Stresses in Crop Plants

RNA interference (RNAi)-based gene silencing has become one of the most successful strategies in not only identifying gene function but also in improving agronomical traits of crops by silencing genes of different pathogens/pests and also plant genes for improvement of desired trait. The conserved nature of RNAi pathway across different organisms increases its applicability in various basic and applied fields. Here we attempt to summarize the knowledge generated on the fundamental mechanisms of RNAi over the years, with emphasis on insects and plant-parasitic nematodes (PPNs). This chapter also reviews the rich history of RNAi research, gene regulation by small RNAs across different organisms, and application potential of RNAi for generating transgenic plants resistant to major pests_. But, there are some limitations too which restrict wider applications of this technology to its full potential. Further refinement of this technology in terms of resolving these shortcomings constitutes one of the thrust areas in present RNAi research. Nevertheless, its application especially in breeding agricultural crops resistant against biotic stresses will certainly offer the possible solutions for some of the breeding objectives which are otherwise unattainable.

The Elusive Search for Reniform Nematode Resistance in Cotton

The reniform nematode (Rotylenchulus reniformis Linford and Oliveira) has emerged as the most important plant-parasitic nematode of cotton in the United States cotton belt. Success in the development of reniform nematode-resistant upland cotton cultivars (Gossypium hirsutum L.) has not been realized despite over three decades of breeding efforts. Research approaches ranging from conventional breeding to triple species hybrids to marker-assisted selection have been employed to introgress reniform nematode resistance from other species of cotton into upland cultivars. Reniform nematode-resistant breeding lines derived from G. longicalyx were developed in 2007. However, these breeding lines displayed stunting symptoms and a hypersensitive response to reniform nematode infection. Subsequent breeding efforts focused on G. barbadense, G. aridum, G. armoreanum, and other species that have a high level of resistance to reniform nematode. Marker-assisted selection has greatly improved screening of reniform nematode-resistant lines. The use of advanced molecular techniques such as CRISPER-Cas9 systems and alternative ways such as delivery of suitable "cry" proteins and specific double-stranded RNA to nematodes will assist in developing resistant cultivars of cotton. In spite of the efforts of cotton breeders and nematologists, successes are limited only to the development of reniform nematode-resistant breeding lines. In this article, we provide an overview of the approaches employed to develop reniform nematode-resistant upland cotton cultivars in the past, progress to date, major obstacles, and some promising future research activity.

Identification, Validation and Utilization of Novel Nematode-Responsive Root-Specific Promoters in Arabidopsis for Inducing Host-Delivered RNAi Mediated Root-Knot Nematode Resistance

The root-knot nematode (RKN), Meloidogyne incognita, is an obligate, sedentary endoparasite that infects a large number of crops and severely affects productivity. The commonly used nematode control strategies have their own limitations. Of late, RNA interference (RNAi) has become a popular approach for the development of nematode resistance in plants. Transgenic crops capable of expressing dsRNAs, specifically in roots for disrupting the parasitic process, offer an effective and efficient means of producing resistant crops. We identified nematode-responsive and root-specific (NRRS) promoters by using microarray data from the public domain and known conserved cis-elements. A set of 51 NRRS genes was identified which was narrowed down further on the basis of presence of cis-elements combined with minimal expression in the absence of nematode infection. The comparative analysis of promoters from the enriched NRRS set, along with earlier reported nematode-responsive genes, led to the identification of specific cis-elements. The promoters of two candidate genes were used to generate transgenic plants harboring promoter GUS constructs and tested in planta against nematodes. Both promoters showed preferential expression upon nematode infection, exclusively in the root in one and galls in the other. One of these NRRS promoters was used to drive the expression of splicing factor, a nematode-specific gene, for generating host-delivered RNAi-mediated nematode-resistant plants. Transgenic lines expressing dsRNA of splicing factor under the NRRS promoter exhibited upto a 32% reduction in number of galls compared to control plants.

Transgenic Strategies for Enhancement of Nematode Resistance in Plants

Plant parasitic nematodes (PPNs) are obligate biotrophic parasites causing serious damage and reduction in crop yields. Several economically important genera parasitize various crop plants. The root-knot, root lesion, and cyst nematodes are the three most economically damaging genera of PPNs on crops within the family Heteroderidae. It is very important to devise various management strategies against PPNs in economically important crop plants. Genetic engineering has proven a promising tool for the development of biotic and abiotic stress tolerance in crop plants. Additionally, the genetic engineering leading to transgenic plants harboring nematode resistance genes has demonstrated its significance in the field of plant nematology. Here, we have discussed the use of genetic engineering for the development of nematode resistance in plants. This review article also provides a detailed account of transgenic strategies for the resistance against PPNs. The strategies include natural resistance genes, cloning of proteinase inhibitor coding genes, anti-nematodal proteins and use of RNA interference to suppress nematode effectors. Furthermore, the manipulation of expression levels of genes induced and suppressed by nematodes has also been suggested as an innovative approach for inducing nematode resistance in plants. The information in this article will provide an array of possibilities to engineer resistance against PPNs in different crop plants.

Genetically engineered bananas resistant to Xanthomonas wilt disease and nematodes

Banana is an important staple food crop feeding more than 100 million Africans, but is subject to severe productivity constraints due to a range of pests and diseases. Banana Xanthomonas wilt caused by Xanthomonas campestris pv. musacearum is capable of entirely destroying a plantation while nematodes can cause losses up to 50% and increase susceptibility to other pests and diseases. Development of improved varieties of banana is fundamental in order to tackle these challenges. However, the sterile nature of the crop and the lack of resistance in Musa germplasm make improvement by traditional breeding techniques either impossible or extremely slow. Recent developments using genetic engineering have begun to address these problems. Transgenic banana expressing sweet pepper Hrap and Pflp genes have demonstrated complete resistance against X. campestris pv. musacearum in the field. Transgenic plantains expressing a cysteine proteinase inhibitors and/or synthetic peptide showed enhanced resistance to a mixed species population of nematodes in the field. Here, we review the genetic engineering technologies which have potential to improve agriculture and food security in Africa.

The Complex Cell Wall Composition of Syncytia Induced by Plant Parasitic Cyst Nematodes Reflects Both Function and Host Plant

Plant-parasitic cyst nematodes induce the formation of specialized feeding structures, syncytia, within their host roots. These unique plant organs serve as the sole nutrient resource for development and reproduction throughout the biotrophic interaction. The multinucleate syncytium, which arises through local dissolution of cell walls and protoplast fusion of multiple adjacent cells, has dense cytoplasm containing numerous organelles, surrounded by thickened outer cell walls that must withstand high turgor pressure. However, little is known about how the constituents of the syncytial cell wall and their conformation support its role during nematode parasitism. We used a set of monoclonal antibodies, targeted to a range of plant cell wall components, to reveal the microstructures of syncytial cell walls induced by four of the most economically important cyst nematode species, Globodera pallida, Heterodera glycines, Heterodera avenae and Heterodera filipjevi, in their respective potato, soybean, and spring wheat host roots. In situ fluorescence analysis revealed highly similar cell wall composition of syncytia induced by G. pallida and H. glycines. Both consisted of abundant xyloglucan, methyl-esterified homogalacturonan and pectic arabinan. In contrast, the walls of syncytia induced in wheat roots by H. avenae and H. filipjevi contain little xyloglucan but are rich in feruloylated xylan and arabinan residues, with variable levels of mixed-linkage glucan. The overall chemical composition of syncytial cell walls reflected the general features of root cell walls of the different host plants. We relate specific components of syncytial cell walls, such as abundant arabinan, methyl-esterification status of pectic homogalacturonan and feruloylation of xylan, to their potential roles in forming a network to support both the strength and flexibility required for syncytium function.

Protease activity and phytocystatin expression in Arabidopsis thaliana upon Heterodera schachtii infection

The activity of plant proteases is important for amino acids recycling, removal of damaged proteins as well as defence responses. The second-stage juvenile of the beet cyst nematode Heterodera schachtii penetrates host roots and induces the feeding site called a syncytium. To determine whether infection by H. schachtii affects proteolysis, the protease activity was studied in Arabidopsis roots and shoots at the day of inoculation and 3, 7 and 15 days post inoculation (dpi). Nematode infection caused a decrease of protease activities in infected roots over the entire examination period at all studied pH values. In contrast, the activities of the low molecular mass as well as Ca²⁺-dependent cysteine proteases were found to be stimulated. In shoots of infected plants, the protease activity was diminished only at 15 dpi at all tested pH values. It was accompanied by changes in total soluble protein content, a higher protein carbonylation and a total polyphenol content. To go deeper into proteolysis regulation, the expression of phytocystatin genes, endogenous inhibitors of cysteine proteases, was examined in syncytia, roots and shoots. Expression of AtCYS1, AtCYS5 and AtCYS6 genes was enhanced upon cyst nematode infection. Our results suggest that changes in protease activities in roots and shoots and altered cystatin expression patterns in syncytia, roots and shoots are important for protein metabolism during cyst nematode infection.

Nuclear receptor nhr-48 is required for pathogenicity of the second stage (J2) of the plant parasite Meloidogyne incognita

Nuclear receptors (NRs) are a diverse class of transcription factors, which are involved in regulating a large number of physiological events in metazoans. However, the function of NRs is poorly understood in plant-parasitic nematodes. Here, members of the NR1J+K group of NRs in nematodes, including the free-living and plant parasites, were examined and phylogenetically analyzed. We found that the number of members of the NR1J+K group in plant-parasitic nematodes was less than that in the free-living nematodes, suggesting this reduction of NR1J+K group members in plant parasites maybe arose during the separation of the free-living and intermediately plant parasitic nematodes (Bursaphelenchus xylophilus). Interestingly, the DNA-binding domain (DBD) and ligand-binding domain (LBD) of NR1J+K members were separated into two gene locations in the plant parasites. Knockdown of Meloidogyne incognita WBMinc13296, the ortholog of Caenorhabditis elegans nhr-48 DBD, reduced infectivity, delayed development, and decreased reproductivity. J2 of M. incognita subjected to silencing of WBMinc13295, the orthologs of B. xylophilus nhr-48 LBD, exhibited developmental lag within the host and reduced reproductivity. This study provides new insights into the function of NRs and suggests that NRs are potential targets for developing effective strategies for biological control of plant-parasitic nematodes.

Expression of a Cystatin Transgene in Eggplant Provides Resistance to Root-knot Nematode, Meloidogyne incognita

Root-knot nematodes (RKN) cause substantial yield decline in eggplant and sustainable management options to minimize crop damage due to nematodes are still limited. A number of genetic engineering strategies have been developed to disrupt the successful plant-nematode interactions. Among them, delivery of proteinase inhibitors from the plant to perturb nematode development and reproduction is arguably the most effective strategy. In the present study, transgenic eggplant expressing a modified rice cystatin (OC-IΔD86) gene under the control of the root-specific promoter, TUB-1, was generated to evaluate the genetically modified nematode resistance. Five putative transformants were selected through PCR and genomic Southern blot analysis. Expression of the cystatin transgene was confirmed in all the events using western blotting, ELISA and qPCR assay. Upon challenge inoculation, all the transgenic events exhibited a detrimental effect on RKN development and reproduction. The best transgenic line (a single copy event) showed 78.3% inhibition in reproductive success of RKN. Our results suggest that cystatins can play an important role for improving nematode resistance in eggplant and their deployment in gene pyramiding strategies with other proteinase inhibitors could ultimately enhance crop yield.

A strong root-specific expression system for stable transgene expression in bread wheat

A strong, stable and root-specific expression system was developed from a rice root-specific GLYCINE - RICH PROTEIN 7 promoter for use as an enabling technology for genetic manipulation of wheat root traits. Root systems play an important role in wheat productivity. Genetic manipulation of wheat root traits often requires a root-specific or root-predominant expression system as an essential enabling technology. In this study, we investigated promoters from rice root-specific or root-predominant expressed genes for development of a root expression system in bread wheat. Transient expression analysis using a GREEN FLUORESCENT PROTEIN (GFP) reporter gene driven by rice promoters identified six promoters that were strongly expressed in wheat roots. Extensive organ specificity analysis of three rice promoters in transgenic wheat revealed that the promoter of rice GLYCINE-RICH PROTEIN 7 (OsGRP7) gene conferred a root-specific expression pattern in wheat. Strong GFP fluorescence in the seminal and branch roots of wheat expressing GFP reporter driven by the OsGRP7 promoter was detected in epidermal, cortical and endodermal cells in mature parts of the root. The GFP reporter driven by the promoter of rice METALLOTHIONEIN-LIKE PROTEIN 1 (OsMTL1) gene was mainly expressed in the roots with essentially no expression in the leaf, stem or seed. However, it was also expressed in floral organs including glume, lemma, palea and awn. In contrast, strong expression of rice RCg2 promoter-driven GFP was found in many tissues. The GFP expression driven by these three rice promoters was stable in transgenic wheat plants through three generations (T1-T3) examined. These data suggest that the OsGRP7 promoter can provide a strong, stable and root-specific expression system for use as an enabling technology for genetic manipulation of wheat root traits.

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

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

Expression of a cystatin transgene can confer resistance to root lesion nematodes in Lilium longiflorum cv. 'Nellie White'

Lilium longiflorum cv. 'Nellie White' assumes a great economic importance as cut flowers, being one of the most valuable species (annual pot plants value above $20,000,000) in terms of wholesales in the US. The root lesion nematode Pratylenchus penetrans (RLN) constitutes one of the main pests for lily producers due to the significant root damage it causes. Our efforts have focused on the generation of soybean hairy roots (as a transient test model) and stable transgenic lilies overexpressing a modified rice cystatin (Oc-IΔD86) transgene and challenged with root lesion nematodes. Lily transformation was achieved by gene gun co-bombardment using both a pBluescript-based vector containing the cystatin gene and pDM307 that contains a bar gene for phosphinothricin selection. Both soybean hairy roots and lilies overexpressing the OcIΔD86 transgene exhibited enhanced resistance to RLN infection by means of nematode reduction up to 75 ± 5% on the total number of nematodes. In addition, lily plants overexpressing OcIΔD86 displayed an increase of plant mass and better growth performance in comparison to wild-type plants, thereby demonstrating an alternative strategy for increasing the yield and reducing nematode damage to this important floral crop.

Pyramiding taro cystatin and fungal chitinase genes driven by a synthetic promoter enhances resistance in tomato to root-knot nematode Meloidogyne incognita

Meloidogyne incognita, one of the major root-knot nematode (RKN) species in agriculture, attacks many plant species, causing severe economic losses. Genetic engineering of plants with defense-responsive genes has been demonstrated to control RKN. These studies, however, focused on controlling RKN at certain growth stages. In the present study, a dual gene overexpression system, utilizing a plant cysteine proteinase inhibitor (CeCPI) and a fungal chitinase (PjCHI-1), was used to transform tomato (Solanum lycopersicum) in order to provide protection from all growth stages of RKN. A synthetic promoter, pMSPOA, containing NOS-like and SP8a elements, was employed to drive the expression of introduced genes. Gall formation and the proportion of female nematodes in the population, as well as effects on the reproduction of RKN, were monitored in both transgenic and control plants. RKN eggs collected from transgenic plants displayed reduced chitin content and retardation in embryogenesis. The results demonstrated that transgenic plants had inhibitory effects on RKN that were superior to plants transformed with a single gene. The pyramiding expression system produced synergistic effects by the two defense-responsive genes, leading to a detrimental effect on all growth stages of RKN.

Field resistance of transgenic plantain to nematodes has potential for future African food security

Plant parasitic nematodes impose losses of up to 70% on plantains and cooking bananas in Africa. Application of nematicides is inappropriate and resistant cultivars are unavailable. Where grown, demand for plantain is more than for other staple crops. Confined field testing demonstrated that transgenic expression of a biosafe, anti-feedant cysteine proteinase inhibitor and an anti-root invasion, non-lethal synthetic peptide confers resistance to plantain against the key nematode pests Radopholus similis and Helicotylenchus multicinctus. The best peptide transgenic line showed improved agronomic performance relative to non-transgenic controls and provided about 99% nematode resistance at harvest of the mother crop. Its yield was about 186% in comparison with the nematode challenged control non-transgenic plants based on larger bunches and diminished plant toppling in storms, due to less root damage. This is strong evidence for utilizing this resistance to support the future food security of 70 million, mainly poor Africans that depend upon plantain as a staple food.

Peptidases compartmentalized to the Ascaris suum intestinal lumen and apical intestinal membrane

The nematode intestine is a tissue of interest for developing new methods of therapy and control of parasitic nematodes. However, biological details of intestinal cell functions remain obscure, as do the proteins and molecular functions located on the apical intestinal membrane (AIM), and within the intestinal lumen (IL) of nematodes. Accordingly, methods were developed to gain a comprehensive identification of peptidases that function in the intestinal tract of adult female Ascaris suum. Peptidase activity was detected in multiple fractions of the A. suum intestine under pH conditions ranging from 5.0 to 8.0. Peptidase class inhibitors were used to characterize these activities. The fractions included whole lysates, membrane enriched fractions, and physiological- and 4 molar urea-perfusates of the intestinal lumen. Concanavalin A (ConA) was confirmed to bind to the AIM, and intestinal proteins affinity isolated on ConA-beads were compared to proteins from membrane and perfusate fractions by mass spectrometry. Twenty-nine predicted peptidases were identified including aspartic, cysteine, and serine peptidases, and an unexpectedly high number (16) of metallopeptidases. Many of these proteins co-localized to multiple fractions, providing independent support for localization to specific intestinal compartments, including the IL and AIM. This unique perfusion model produced the most comprehensive view of likely digestive peptidases that function in these intestinal compartments of A. suum, or any nematode. This model offers a means to directly determine functions of these proteins in the A. suum intestine and, more generally, deduce the wide array functions that exist in these cellular compartments of the nematode intestine.

Past research has demonstrated that the nematode intestine has value for developing new methods of therapy and control of parasitic nematodes, as related to both vaccines and other anthelmintics. Yet, information related to basic intestinal cell biology is very limited. Research progress reported here moves towards the comprehensive identification of proteins (peptidases and others), and hence functions, that are sited on the apical intestinal membrane and within the intestinal lumen of adult female Ascaris suum. These advances provide an unprecedented research model to determine critical functions sited at these locations and to develop approaches to inhibit those functions. Comparative analysis among diverse parasitic species raises expectations that the results from A. suum can be applied to many parasitic nematodes for which similar research is technically impossible to perform.

Agrobacterium-mediated genetic transformation of yam (Dioscorea rotundata): an important tool for functional study of genes and crop improvement

Although genetic transformation of clonally propagated crops has been widely studied as a tool for crop improvement and as a vital part of the development of functional genomics resources, there has been no report of any existing Agrobacterium-mediated transformation of yam (Dioscorea spp.) with evidence of stable integration of T-DNA. Yam is an important crop in the tropics and subtropics providing food security and income to over 300 million people. However, yam production remains constrained by increasing levels of field and storage pests and diseases. A major constraint to the development of biotechnological approaches for yam improvement has been the lack of an efficient and robust transformation and regeneration system. In this study, we developed an Agrobacterium-mediated transformation of Dioscorea rotundata using axillary buds as explants. Two cultivars of D. rotundata were transformed using Agrobacterium tumefaciens harboring the binary vectors containing selectable marker and reporter genes. After selection with appropriate concentrations of antibiotic, shoots were developed on shoot induction and elongation medium. The elongated antibiotic-resistant shoots were subsequently rooted on medium supplemented with selection agent. Successful transformation was confirmed by polymerase chain reaction, Southern blot analysis, and reporter genes assay. Expression of gusA gene in transgenic plants was also verified by reverse transcription polymerase chain reaction analysis. Transformation efficiency varied from 9.4 to 18.2% depending on the cultivars, selectable marker genes, and the Agrobacterium strain used for transformation. It took 3-4 months from Agro-infection to regeneration of complete transgenic plant. Here we report an efficient, fast and reproducible protocol for Agrobacterium-mediated transformation of D. rotundata using axillary buds as explants, which provides a useful platform for future genetic engineering studies in this economically important crop.

Identification of genes involved in the response of Arabidopsis to simultaneous biotic and abiotic stresses

In field conditions, plants may experience numerous environmental stresses at any one time. Research suggests that the plant response to multiple stresses is different from that for individual stresses, producing nonadditive effects. In particular, the molecular signaling pathways controlling biotic and abiotic stress responses may interact and antagonize one another. The transcriptome response of Arabidopsis (Arabidopsis thaliana) to concurrent water deficit (abiotic stress) and infection with the plant-parasitic nematode Heterodera schachtii (biotic stress) was analyzed by microarray. A unique program of gene expression was activated in response to a combination of water deficit and nematode stress, with 50 specifically multiple-stress-regulated genes. Candidate genes with potential roles in controlling the response to multiple stresses were selected and functionally characterized. RAPID ALKALINIZATION FACTOR-LIKE8 (AtRALFL8) was induced in roots by joint stresses but conferred susceptibility to drought stress and nematode infection when overexpressed. Constitutively expressing plants had stunted root systems and extended root hairs. Plants may produce signal peptides such as AtRALFL8 to induce cell wall remodeling in response to multiple stresses. The methionine homeostasis gene METHIONINE GAMMA LYASE (AtMGL) was up-regulated by dual stress in leaves, conferring resistance to nematodes when overexpressed. It may regulate methionine metabolism under conditions of multiple stresses. AZELAIC ACID INDUCED1 (AZI1), involved in defense priming in systemic plant immunity, was down-regulated in leaves by joint stress and conferred drought susceptibility when overexpressed, potentially as part of abscisic acid-induced repression of pathogen response genes. The results highlight the complex nature of multiple stress responses and confirm the importance of studying plant stress factors in combination.

Ethylene signaling pathway modulates attractiveness of host roots to the root-knot nematode Meloidogyne hapla

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

Kiwifruit allergies

While kiwifruit has a high nutritive and health value, a small proportion of the world's population appears to be allergic to the fruit. IgE-mediated kiwifruit allergy is often associated with birch and grass pollinosis as well as with latex allergy. Isolated allergy to kiwifruit is also relatively common and often severe. Eleven green kiwifruit (Actinidia deliciosa cv. Hayward) allergens recognized to date are termed as Act d 1 through Act d 11. Bet v 1 homologue (Act d 8) and profilin (Act d 9) are important allergens in polysensitized subjects, whereas actinidin (Act d 1) is important in kiwifruit monosensitized subjects. Differences in allergenicity have been found among kiwifruit cultivars. Allergy sufferers might benefit from the selection and breeding of low-allergenic kiwifruit cultivars.

Generation of transgenic plantain (Musa spp.) with resistance to plant pathogenic nematodes

Plant parasitic nematodes impose a severe constraint on plantain and banana productivity; however, the sterile nature of many cultivars precludes conventional breeding for resistance. Transgenic plantain cv. Gonja manjaya (Musa AAB) plants, expressing a maize cystatin that inhibits nematode digestive cysteine proteinases and a synthetic peptide that disrupts nematode chemoreception, were assessed for their ability to resist nematode infection. Lines were generated that expressed each gene singly or both together in a stacked defence. Nematode challenge with a single species or a mixed population identified 10 lines with significant resistance. The best level of resistance achieved against the major pest species Radopholus similis was 84% ± 8% for the cystatin, 66% ± 14% for the peptide and 70% ± 6% for the dual defence. In the mixed population, trial resistance was also demonstrated to Helicotylenchus multicinctus. A fluorescently labelled form of the chemodisruptive peptide underwent retrograde transport along certain sensory dendrites of R. similis as required to disrupt chemoreception. The peptide was degraded after 30 min in simulated intestinal fluid or boiling water and after 1 h in nonsterile soil. In silico sequence analysis suggests that the peptide is not a mammalian antigen. This work establishes the mode of action of a novel nematode defence, develops the evidence for its safe and effective deployment against multiple nematode species and identifies transgenic plantain lines with a high level of resistance for a proposed field trial.

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.

Evaluation of in vitro and in vivo effects of semipurified proteinase inhibitors from Theobroma seeds on midgut protease activity of Lepidopteran pest insects

We have characterized in vitro and in vivo effects of trypsin inhibitors from Theobroma seeds on the activity of trypsin- and chymotrypsin-like proteins from Lepidopteran pest insects. The action of semipurified trypsin inhibitors from Theobroma was evaluated by the inhibition of bovine trypsin and chymotrypsin activities determined by the hydrolysis of N-Benzoyl-DL-Arginine-p-Nitroanilide (BAPA) and N-Succinyl-Ala-Ala-Pho-Phe p-Nitroanilide (S-(Ala)2ProPhe-pNA). Proteinase inhibitor activities from Theobroma cacao and T. obovatum seeds were the most effective in inhibiting trypsin-like proteins, whereas those from T. obovatum and T. sylvestre were the most efficient against chymotrypsin-like proteins. All larvae midgut extracts showed trypsin-like proteolytic activities, and the putative trypsin inhibitors from Theobroma seeds significantly inhibited purified bovine trypsin. With respect to the influence of Theobroma trypsin inhibitors on intact insects, the inclusion of T. cacao extracts in artificial diets of velvet bean caterpillars (Anticarsia gemmatalis) and sugarcane borer (Diatraea saccharalis) produced a significant increase in the percentage of adult deformation, which is directly related to both the survival rate of the insects and oviposition.

Cloning of a cystatin gene from sugar beet M14 that can enhance plant salt tolerance

An open reading frame encoding a cysteine protease inhibitor, cystatin was isolated from the buds of sugar beet monosomic addition line M14 (BvM14) using 5'-/3'-RACE method. It encoded a polypeptide of 104 amino acids with conserved G and PW motifs, the consensus phytocystatin sequence LARFAV and the active site QVVAG. The protein showed significant homology to other plant cystatins. BvM14-cystatin was expressed ubiquitously in roots, stems, leaves and flower tissues with relatively high abundance in developing stems and roots. It was found to be localized in the nucleus, cytoplasm and plasma membrane. Recombinant BvM14-cystatin expressed in Escherichia coli was purified and it exhibited cysteine protease inhibitor activity. Salt-stress treatment induced BvM14-cystatin transcript levels in the M14 seedlings. Homozygous Arabidopsis plants over-expressing BvM14-cystatin showed enhanced salt tolerance. Taken together, these data improved understanding of the functions of BvM14-cystatin and highlighted the possibility of employing the cystatin in engineering plants for enhanced salt tolerance.

Molecular analysis of maize cystatin expression as fusion product in Escherichia coli

Nowadays, plant cysteine proteinase inhibitors "namely phytocystatins" have attracted researchers towards the identification of their molecular structures and novel physiological functions. Their important roles in plant developmental processes and different stress responses have been well known. In spite of advances in the understanding of phytocystatins, we lack enough data concerning their heterologous expression especially in the forms of fusion products that are most important whether for biochemical, pharmacological or clinical studies. The present work describes an easy method of expression, purification and functional characterization in Escherichia coli of maize cystatin as a part of maltose-binding fusion protein. Assessments revealed that upon expression of fused product the total antioxidation status of the induced recombinant cells is increased. This result leads to question 'Is there any parallel functional correlation between anti-proteolytic and anti-oxidative systems?' However, the present research will open a gate for the new studies regarding the putative communicative roles of these systems that may be existing in the biological world.

Biofumigation for control of pale potato cyst nematodes: activity of brassica leaf extracts and green manures on Globodera pallida in vitro and in soil

The effects of brassica green manures on Globodera pallida were assessed in vitro and in soil microcosms. Twelve of 22 brassica accessions significantly inhibited the motility of G. pallida infective juveniles in vitro. Green manures of selected brassicas were then incorporated into soil containing encysted eggs of G. pallida. Their effect on egg viability was estimated by quantifying nematode actin 1 mRNA by RT-qPCR. The leaf glucosinolate profiles of the plants were determined by high-performance liquid chromatography. Three Brassica juncea lines (Nemfix, Fumus, and ISCI99) containing high concentrations of 2-propenyl glucosinolate were the most effective, causing over 95% mortality of encysted eggs of G. pallida in polyethylene-covered soil. The toxic effects of green manures were greater in polyethylene-covered than in open soil. Toxicity in soil correlated with the concentration of isothiocyanate-producing glucosinolate but not total glucosinolate in green manures.

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

We investigated what gene(s) in the plant roots have the positive role against repressing root-knot nematode (RKN) infection. We investigated the interaction between RKN infection and gene expression in the plant roots induced by methyl jasmonate (MeJA). We focused on the induced resistance response and the duration after foliar treatment with MeJA of 0.1, 0.5, 1.0, and 5.0mM at 1, 24, 48, and 72h prior to the inoculation of RKN. As a result, the foliar treatment with MeJA at 0.5mM or higher concentrations significantly reduced the infection of RKN in plants and the effect lasted for about 1 week. The repressing effect on RKN population declined to the lowest level in two weeks after MeJA treatment. The expression of proteinase inhibitors (PIs) and multicystatin (MC) were induced while the repressing effect on RKN was valid and a negative correlation was found between the expression of PIs or MC and RKN infection. In addition, when tomato plants no longer expressing MC and PIs were treated again with MeJA, the repressing effect revived. These phenomena appeared to be regardless of the existence of Mi-genes or isolate of RKN. Our results indicate that the expression level of MC and PIs may be effective as marker genes for estimating the induced resistance response against RKN infection.

Data-mining of the Meloidogyne incognita degradome and comparative analysis of proteases in nematodes

Proteases perform essential physiological functions in all living organisms. In parasitic helminths, they are of particular importance for tissue penetration, digestion of host tissues for nutrition, and evasion of host immune responses. The recent availability of the genome sequence of the nematode Meloidogyne incognita has allowed the analysis of the protease repertoire of this major crop pathogen. The M. incognita degradome consists of at least 334 proteases that are distributed into 43 families of the five known catalytic classes. Expression profiling identified protease genes with a differential transcript level between eggs and infective juveniles. Comparing the M. incognita degradome with those of five other nematodes showed discrepancies in the distribution of some protease families, including large expansion in some families, that could reflect specific aspects of the parasitic lifestyle of this organism. This comparative study should provide a framework for deciphering the diversity of protease-mediated functions in nematodes.

Isolation and partial sequence of a Kunitz-type elastase specific inhibitor from marama bean (Tylosema esculentum)

An isolation procedure utilizing ammonium sulfate fractionation and affinity chromatography was used to purify an elastase inhibitor present in large amounts in marama beans (Tylosema esculentum). The protein appeared to be heterogeneous due to carbohydrate differences, demonstrating two bands on SDS gels with molecular weights of 17.8 kDa and 20 kDa. Partial sequence, derived from mass spectrometry, indicated that the protein is a Kunitz-type inhibitor distinct from other known plant serine protease inhibitors. The marama bean inhibitor is specific for elastase, with very low K(i) for both pancreatic and neutrophil elastase. The quantity of elastase inhibitor present in marama beans is many times greater than in soybean or any other bean or nut source reported to date. This raises the question of why a bean found in an arid corner of the Kalahari Desert would be so rich in a very potent elastase inhibitor.

Effects of a novel pathogenesis-related class 10 (PR-10) protein from Crotalaria pallida Roots with papain inhibitory activity against root-knot nematode Meloidogyne incognita

A novel pathogenesis-related class 10 (PR-10) protein with papain inhibitory activity, named CpPRI, was purified from Crotalaria pallida roots by ammonium sulfate precipitation followed by three reverse-phase high-performance liquid chromatographies (HPLCs). CpPRI is made up of a single polypeptide chain with a M(r) of 15 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This protein exhibited a K(i) value of 1.8 x 10(-9) M and operates via a noncompetitive inhibition mechanism. The alignment of the N-terminal amino acid sequence of CpPRI with other proteins revealed its identity with PR-10 proteins. CpPRI acts against digestive proteinase from root-knot nematode Meloidogyne incognita and demonstrated nematostatic and nematicide effects on this parasite in bioassays. In a localization study, fluorescein-5-isothiocyanate (FITC)-CpPRI was observed to internalize and diffuse over the entire J2 body after 6 h of incubation. This fact could explain the natural tolerance of this plant species to nematodes.

Heterologous expression of taro cystatin protects transgenic tomato against Meloidogyne incognita infection by means of interfering sex determination and suppressing gall formation

Plant-parasitic nematodes are a major pest of many plant species and cause global economic loss. A phytocystatin gene, Colocasia esculenta cysteine proteinase inhibitor (CeCPI), isolated from a local taro Kaosiang No. 1, and driven by a CaMV35S promoter was delivered into CLN2468D, a heat-tolerant cultivar of tomato (Solanum lycopersicum). When infected with Meloidogyne incognita, one of root-knot nematode (RKN) species, transgenic T1 lines overexpressing CeCPI suppressed gall formation as evidenced by a pronounced reduction in gall numbers. In comparison with wild-type plants, a much lower proportion of female nematodes without growth retardation was observed in transgenic plants. A decrease of RKN egg mass in transgenic plants indicated seriously impaired fecundity. Overexpression of CeCPI in transgenic tomato has inhibitory functions not only in the early RKN infection stage but also in the production of offspring, which may result from intervention in sex determination.

The potential of genetically enhanced plants to address food insecurity

Food insecurity is one of the most important social issues faced today, with 840 million individuals enduring chronic hunger and three billion individuals suffering from nutrient deficiencies. Most of these individuals are poverty stricken and live in developing countries. Strategies to address food insecurity must aim to increase agricultural productivity in the developing world in order to tackle poverty, and must provide long-term improvements in crop yields to keep up with demand as the world's population grows. Genetically enhanced plants provide one route to sustainable higher yields, either by increasing the intrinsic yield capability of crop plants or by protecting them from biotic and abiotic constraints. The present paper discusses a range of transgenic approaches that could increase agricultural productivity if applied on a large scale, including the introduction of genes that confer resistance to pests and diseases, or tolerance of harsh environments, and genes that help to lift the intrinsic yield capacity by increasing metabolic flux towards storage carbohydrates, proteins and oils. The paper also explores how the nutritional value of plants can be improved by genetic engineering. Transgenic plants, as a component of integrated strategies to relieve poverty and deliver sustainable agriculture to subsistence farmers in developing countries, could have a significant impact on food security now and in the future.

An extended AE-rich N-terminal trunk in secreted pineapple cystatin enhances inhibition of fruit bromelain and is posttranslationally removed during ripening

Phytocystatins are potent inhibitors of cysteine proteases and have been shown to participate in senescence, seed and organ biogenesis, and plant defense. However, phytocystatins are generally poor inhibitors of the cysteine protease, bromelain, of pineapple (Ananas comosus). Here, we demonstrated that pineapple cystatin, AcCYS1, inhibited (>95%) stem and fruit bromelain. AcCYS1 is a unique cystatin in that it contains an extended N-terminal trunk (NTT) of 63 residues rich in alanine and glutamate. A signal peptide preceding the NTT is processed in vitro by microsomal membranes giving rise to a 27-kD species. AcCYS1 mRNA was present in roots and leaves but was most abundant in fruit. Using immunofluorescence and immunoelectron microscopy with an AcCYS1-specific antiserum, AcCYS1 was found in the apoplasm. Immunoblot analysis identified a 27-kD protein in fruit, roots, and leaves and a 15-kD species in mature ripe fruit. Ripe fruit extracts proteolytically removed the NTT of 27-kD AcCYS1 in vitro to produce the 15-kD species. Mass spectrometry analysis was used to map the primary cleavage site immediately after a conserved critical glycine-94. The AE-rich NTT was required to inhibit fruit and stem bromelain (>95%), whereas its removal decreased inhibition to 20% (fruit) and 80% (stem) and increased the dissociation equilibrium constant by 1.8-fold as determined by surface plasmon resonance assays. We propose that proteolytic removal of the NTT results in the decrease of the inhibitory potency of AcCYS1 against fruit bromelain during fruit ripening to increase tissue proteolysis, softening, and degradation.

Protective effects of a cysteine proteinase propeptide expressed in transgenic soybean roots

Sedentary endoparasitic nematodes cause extensive damage to a large number of ornamental plants and food crops, with estimated economical losses over 100 billion US$ worldwide. Various efforts have put forth in order to minimize nematode damage, which typically involve the use of nematicides that have high cost and enhanced toxicity to humans and the environment. Additionally, different strategies have been applied in order to develop genetically modified plants with improved nematode resistance. Among the strategies are anti-invasion and migration, feeding-cell attenuation, and anti-nematode feeding. In the present study, we focus on anti-nematode feeding, which involves the evaluation and potential use of the cysteine proteinase (CPs) propeptide as a control alternative. The cysteine proteinase prodomain, isolated from Heterodera glycines (HGCP prodomain), is a natural inhibitory peptide used to transform soybean cotyledons using Agrobacterium rhizogenes. Genetically modified soybean roots expressing the propeptide were detected by Western blot and expression levels were measured by ELISA (around 0.3%). The transgenic roots expressing the propeptide were inoculated with a thousand H. glycines at the second juvenile stage, and a remarkable reduction in the number of females and eggs was observed. A reduction of female length and diameter was also observed after 35 days post-inoculation. Furthermore, the H. glycines mature protein was detected in females fed on soybean transformed root expressing or not expressing the propeptide. The data presented here indicate that the HGCP propeptide can reduce soybean cyst nematode infection and this strategy could be applied in the near future to generate resistant crop cultivars.

Expression of v-cath gene from HearNPV in tobacco confers an antifeedant effect against Helicoverpa armigera

Biotechnology solutions for insect control on crops largely depend on the expression of Bacillus thuringiensis insecticidal proteins to kill pests. V-CATH, a cathepsin L-like cysteine protease from baculoviruses, has been shown to play an essential role in host insect liquefaction. In this study, the v-cath gene from Helicoverpa armigera single nucleopolyhedrovirus (HearNPV) was cloned into the pBI121 binary vector under the control of CaMV35S promoter, and was expressed in tobacco via Agrobacterium-mediated transformation. PCR and RT-PCR analyses of T(1) kanamycin-resistant tobacco progeny plants confirmed the integration and transcription of the v-cath gene. Using a leaf-disk bioassay, antifeedant activity toward H. armigera was tested. Our result showed that, when feeding the first-instar larvae of H. armigera with leaves of transgenic plants, the v-cath transgene expression has a profound antifeedant effect. Most importantly, the growth and development of the insect were inhibited when transferred from leaf-feeding to artificial diet. Our result demonstrated that v-cath gene from baculovirus induced antifeedant effect against H. armigera, resulted in larval stunting and retarded insect development, and has the potential to be used as an alternative way to generate transgenic plants for insect pest control.

Plant pathogenesis-related (PR) proteins: a focus on PR peptides

The novel classes of plant pathogenesis-related (PR) proteins identified during the last decade also include novel peptide families. This review specifically focuses on these pathogenesis-related peptides, including proteinase inhibitors (PR-6 family), plant defensins (PR-12 family), thionins (PR-13 family) and lipid transfer proteins (PR-14 family). For each family of PR peptides, the general features concerning occurrence, expression and possible functions of their members are described. Next, more specifically the occurrence of each PR peptide family in the model plant Arabidopsis thaliana is discussed. Single-gene studies performed on particular gene members of a PR peptide family are reported. In addition, expression data of yet undescribed gene members of that particular PR peptide family are presented by consultation of publicly available micro-array databases. Finally an update is provided on the potential role of these PR peptides in A. thaliana, with a focus on their possible involvement in plant defense.