The first isolated collagen gene of the root-knot nematode Meloidogyne javanica is developmentally regulated

Populations of Heterodera schachtii Differ in Susceptibility to Rhizosphere Bacteria Structured by Plant Age

Rhizosphere microbes, particularly bacteria, are essential for controlling plant-parasitic nematodes (PPNs) through various mechanisms. However, the plant's age and the genetic composition of nematode populations can significantly influence the inhibitory effectiveness of these microbes against the beet cyst nematode Heterodera schachtii. In this study, rhizosphere microbes were isolated from 39-day-old and 69-day-old resistant oilseed radish plants to evaluate their impact on the penetration of the second-stage juveniles (J2s) originating from four genetically distinct H. schachtii populations. The suppression of J2s penetration by the attached microbes varied across the nematode populations, which displayed differing levels of aggressiveness toward the resistant oilseed radish. Furthermore, differences in the alpha and beta diversity of rhizosphere bacteria were observed between the 39-day-old and 69-day-old plants, leading to variations in the bacterial attachment among the four nematode populations. In summary, the effectiveness of resistant catch crops against H. schachtii is influenced by the pathogenicity of the nematode populations and their interactions with the rhizosphere microbial community shaped by the plant's age.

The Difference in the Bacterial Attachment among Pratylenchus neglectus Populations and Its Effect on the Nematode Infection

Different bacterial isolates attach to the cuticle of plant-parasitic nematodes, affecting their interactions with the host plant. Nematode populations differ in their genetic and cuticle structures, causing variable interactions with host plants and natural enemies. In the current study, attachment assays were carried out to compare the attachment of soil bacteria in general and the bacterial isolate of Rothia sp. in particular among geographically diverse populations of Pratylenchus neglectus. Biological and molecular assays were further conducted to examine the effect of Rothia attachment on nematode penetration into barley roots and to sequence the fatty acid- and retinol-binding gene (Pn-far-1). The results showed that nematode populations of P. neglectus differed in their bacterial attachment. Soil bacteria and Rothia sp. attached specifically to the cuticle of P. neglectus and did so differently among the nematode populations. Rothia attachment caused a reduction in the infectivity of three nematode populations in barley roots. The sequencing of the far-1 gene revealed genetic variability within and among P. neglectus populations. In conclusion, the interaction between P. neglectus and their bacterial attachers occurs in a population-specific manner, elucidating an essential aspect of using biological agents to manage plant-parasitic nematodes. Key Message: 1. Geographically diverse populations of the root lesion nematode Pratylenchus neglectus differed in the soil bacterial communities attached to their cuticles. 2. The bacterial isolate of Rothia sp. attached to the cuticle of P. neglectus and reduced its penetration into the host plant in a population-specific manner. 3. The fatty acid- and retinol-binding gene (far-1) varied within and among P. neglectus populations with their different bacterial attachment.

Isolation, cloning, and characterization of a cuticle collagen gene, Mi-col-5, in Meloidogyne incognita

Cuticle collagens form a major part of the nematode cuticle and are responsible for maintaining the overall shape of the animal and its protection from the external environment. Although substantial research on cuticle collagen genes has been carried out in Caenorhabditis elegans, their isolation and characterization in plant parasitic nematodes have been limited to a few genes only. In this study, a cuticle collagen gene, Mi-col-5, was isolated from root-knot nematode, Meloidogyne incognita. A partial segment of 402 bp was first cloned and analyzed on Gbrowse followed by subsequent cloning of the 1047 bp long full cDNA specifying the open reading frame. The deduced amino acid sequence showed 92% sequence identity with that of Mj-col-5. However, a transmembrane helix was predicted in Mi-col-5 which was not present in Mj-col-5. The conserved pattern of cysteine residues in Mi-col-5 suggested that it belonged to group 2 of nematode cuticle collagens but with a longer carboxy terminal region as was the case with Mj-col-5. Domain prediction revealed the presence of a nematode cuticle collagen N terminal domain and a pfam collagen domain along with collagen triple helix repeats. A phylogenetic tree based on the amino acid sequences showed evolutionary relationship of Mi-col-5 with cuticle collagens genes of other nematodes. 3D models for Mi-col-5 were predicted with the best confidence score of -2.78. Expression of Mi-col-5 transcript was found to be maximum in egg masses followed by adult females and J2s suggesting its role in the early stages of the development of the nematode during its life cycle.

Potent nematicidal activity of phthalaldehyde, salicylaldehyde, and cinnamic aldehyde against Meloidogyne incognita

The nematicidal activity of selected aromatic aldehydes was tested against the root knot nematode Meloidogyne incognita. The most active aldehyde was phthalaldehyde (1) with an EC(50) value of 11 ± 6 mg/L followed by salicylaldehyde (2) and cinnamic aldehyde (3) with EC(50) values of 11 ± 1 and 12 ± 5 mg/L, respectively. On the other hand, structurally related aldehydes such as 2-methoxybenzaldehyde (21), 3,4-dimethoxybenzaldehyde, and vanillin (23) were not active at the concentration of 1000 mg/L. By liquid chromatography-mass spectrometry the reactivity of tested aldehydes against a synthetic peptide resembling the nematode cuticle was characterized. At the test concentration of 1 mM, the main adduct formation was observed for 3,4-dihydroxybenzaldehyde (22), 2-methoxybenzaldehyde (21), and 3,4-dimethoxybenzaldehyde. Considering that 2-methoxybenzaldehyde (21) and 3,4-dimethoxybenzaldehyde were not active against M. incognita in in vitro experiments led us to hypothesize a different mechanism of action rather than an effect on the external cuticle modification of nematodes. When the toxicity of the V-ATPase inhibitor pyocyanin (10) was tested against M. incognita J2 nematodes, an EC(50) at 24 h of 72 ± 25 mg/L was found. The redox-active compounds such as phthalaldehyde (1) and salicylaldehyde (2) may share a common mode of action inhibiting nematode V-ATPase enzyme. The results of this investigation reveal that aromatic redox-active aldehydes can be considered as potent nematicides, and further investigation is needed to completely clarify their mode of action.

Unravelling the moulting degradome: new opportunities for chemotherapy?

Replacement of the nematode cuticle with a newly synthesized cuticle (a process known as moulting) occurs four times during larval development. Therefore, the key components of this essential developmental process represent attractive targets for new chemotherapeutic strategies. Recent advances in understanding the molecular genetics of nematode moulting should stimulate and facilitate development of novel drugs that target the essential molecules of the moulting cycle. In particular, we argue that further understanding of the moulting degradome and its key peptidase members offers an important opportunity for the development of novel antinematode agents.

Isolation and characterization of a cDNA encoding a serine proteinase from the root-knot nematode Meloidogyne incognita

This report describes the first serine proteinase gene isolated from the sedentary nematode Meloidogyne incognita. Using degenerate primers, a 1372bp cDNA encoding a chymotrypsin-like serine proteinase (Mi-ser1) was amplified from total RNA of adult females by RT-PCR and 5' and 3' rapid amplification of cDNA ends. The deduced amino acid sequence of Mi-ser1 encoded a putative signal peptide and a prodomain of 22 and 33 amino acids, respectively, and a mature proteinase of 341 amino acids with a predicted molecular mass of 37,680Da. Sequence identity with the top serine proteinases matches from the databases ranged from 23 to 27%, including sequences from insects, mammals, and other nematodes. Southern blot analysis suggested that Mi-ser1 is encoded by a single or few gene copies. The pattern of developmental expression analyzed by Northern blot and RT-PCR indicated that Mi-ser1 was transcribed mainly in females. The domain architecture composed of a single chymotrypsin-like catalytic domain and the detection of a putative signal peptide suggested a digestive role for Mi-ser1.

Enzymes involved in the biogenesis of the nematode cuticle

Nematodes include species that are significant parasites of man, his domestic animals and crops, and cause chronic debilitating diseases in the developing world; such as lymphatic filariasis and river blindness caused by filarial species. Around one third of the World's population harbour parasitic nematodes; no vaccines exist for prevention of infection, limited effective drugs are available and drug resistance is an ever-increasing problem. A critical structure of the nematode is the protective cuticle, a collagen-rich extracellular matrix (ECM) that forms the exoskeleton, and is critical for viability. This resilient structure is synthesized sequentially five times during nematode development and offers protection from the environment, including the hosts' immune response. The detailed characterization of this complex structure; it's components, and the means by which they are synthesized, modified, processed and assembled will identify targets that may be exploited in the future control of parasitic nematodes. This review will focus on the nematode cuticle. This structure is predominantly composed of collagens, a class of proteins that are modified by a range of co- and post-translational modifications prior to assembly into higher order complexes or ECMs. The collagens and their associated enzymes have been comprehensively characterized in vertebrate systems and some of these studies will be addressed in this review. Conversely, the biosynthesis of this class of essential structural proteins has not been studied in such detail in the nematodes. As with all morphogenetic, functional and developmental studies in the Nematoda phylum, the free-living species Caenorhabditis elegans has proven to be invaluable in the characterization of the cuticle and the cuticle collagen gene family, and is now proving to be an excellent model in the study of cuticle collagen biosynthetic enzymes. This model system will be the main focus of this review.

Immunolocalization of a putative cuticular collagen protein in several developmental stages of Meloidogyne arenaria, Globodera pallida and G. rostochiensis

The monoclonal antibody IACR-CCNj.3d has previously been used to isolate a gene (gp-col-8) with strong similarity to cuticular collagen from a mixed stage Globodera pallida cDNA expression library. The antibody has also been shown to label specifically the amphidial canal of pre-parasitic second stage juveniles (J2) of several plant nematode species without any reactivity on the cuticular surface, indicating that this protein is either not present or is inaccessible on the cuticular surface. This paper investigates the cross-reactivity of Mab IACR-CCNj.3d with Meloidogyne arenaria and the localization of the putative collagen protein on the cuticular surface of parasitic stages in planta and on the cuticular surface of juveniles inside eggs. The antigen was shown to be present in all developmental stages of the two species of potato cyst nematodes and M. arenaria. The antibody bound strongly to the amphidial canal and hypodermis of pre-parasitic J2 and adult females. The antigen was present on the cuticular surface of the sausage-shaped J2 in planta and of first stage juveniles (J1) inside the eggs. The presence of collagen on the surface of the cuticle of moulting stages of plant parasitic nematodes has been observed for the first time. It is clear that this protein has a role in the construction of the cuticle of the first stage juveniles and parasitic second stage juveniles, during moulting inside the eggs and in the root tissue, respectively.

Isolation of a novel collagen gene (Mj-col-5) in Meloidogyne javanica and analysis of its expression pattern

Mj-col-5, isolated from the plant parasitic nematode Meloidogyne javanica, has a longer carboxy-terminus than other members of the Caenorhabditis elegans COL-6 subfamily of cuticle collagen, including an extra tyrosine residue, and may form altered nonreducible cross-linkages. By semiquantitative determination at different life stages, Mj-col-5 transcript was shown to be more abundant in eggs than in juveniles/young females and adult females. To characterize further this gene's contribution to the changing cuticle of the nematode, we expressed a fusion protein containing a nonconserved 58-amino-acid sequence from the putative Mj-col-5 gene product and raised rabbit antiserum against the fusion protein. The antiserum detected a strongly reacting band (36 kDa, designated MJE36) on western blots of M. javanica eggs extracted with beta-mercaptoethanol. MJE36 was sensitive to collagenase and was not detected on western blots of extracts from M. javanica second-stage juveniles or adult females. A band of the same molecular size was detected in Meloidogyne incognita egg extracts but not in those of Heterodera avenae. Immunoblot indicated that MJE36 is not present in egg shells of M. javanica.

Alterations in the levels of glycogen and glycogen synthase transcripts during desiccation in the insect-killing nematode Steinernema feltiae IS-6

The ability to withstand desiccation by entering anhydrobiosis is important for the survival of many nematode species. We are interested in the metabolic changes that occur during dehydration in the semiarid strain IS-6 of the insect parasitic nematode Steinernema feltiae. These changes may enable IS6 to be more tolerant to desiccation than temperate strains. We identified genes of IS-6 that exhibit changes in transcript levels during dehydration. These included glycogen synthase (Sf-gsy-1), which is the rate-limiting enzyme in the synthesis of glycogen, which is likely to play a role in desiccation survival. We established the changes in the steady state level of Sf-gsy-1 transcripts upon dehydration and determined the biochemical changes in the level of its product, glycogen, during the dehydration and rehydration of nematodes. Our results suggest a shift from glycogen to trehalose synthesis during dehydration, which is regulated at least in part by suppression of glycogen synthase transcription.

Characterisation of a collagen gene subfamily from the potato cyst nematode Globodera pallida

We have isolated two full-length genomic DNA sequences, which encode the cuticle collagen proteins GP-COL-1 and GP-COL-2, from the potato cyst nematode Globodera pallida. A third, partial collagen gene ORF termed gp-col-t(t=truncated) has also been isolated and appears to represent an unexpressed pseudogene. The gp-col-1 and gp-col-2 genes both contain three short (<97 bp) introns which disrupt coding regions predicted to specify proteins with molecular weights of 33 and 32.7 kDa respectively. All three sequences show high similarity to each other and to the previously isolated G. pallida cDNA clone gp-col-8. The conserved pattern of cysteine residues and non-(Gly-X-Y)(n) region sequence similarity observed in all four G. pallida genes suggests that these molecules form part of the same subfamily of collagens. Southern analysis indicates that this subfamily is likely to contain further members. The G. pallida collagen sequences show striking similarity to twelve genes from Caenorhabditis elegans which collectively represent the recently classified Group 1a collagen subfamily. No data exists on the function of this subfamily in C. elegans. gp-col-1 and gp-col-2 are developmentally regulated with transcripts of both genes detected in adult virgin and gravid females but not in pre-parasitic second stage juveniles. A similar expression pattern is observed for the Group 1a collagen lemmi 5 from Meloidogyne incognita perhaps indicating a generic link between subfamily and function during the various changes in cuticular structure which accompany nematode growth and reproduction. Immunochemical studies indicate that the GP-COL-1 protein is specifically located in the hypodermis of G. pallida adult females.

Cuticle collagen genes. Expression in Caenorhabditis elegans

Collagen is a structural protein used in the generation of a wide variety of animal extracellular matrices. The exoskeleton of the free-living nematode, Caenorhabditis elegans, is a complex collagen matrix that is tractable to genetic research. Mutations in individual cuticle collagen genes can cause exoskeletal defects that alter the shape of the animal. The complete sequence of the C. elegans genome indicates upwards of 150 distinct collagen genes that probably contribute to this structure. During the synthesis of this matrix, individual collagen genes are expressed in distinct temporal periods, which might facilitate the formation of specific interactions between distinct collagens.

Comparison of FaRP immunoreactivity in free-living nematodes and in the plant-parasitic nematode Heterodera glycines

The family of FMRFamide-related peptides (FaRPs) is widely distributed among invertebrates, where the peptides serve as neuromodulators. Published reports indicate that numerous FaRP sequences exist in free-living and animal parasitic nematodes. Using a FMRFamide ELISA, FaRP immunoreactivity was detected in extracts of the soybean cyst nematode, Heterodera glycines, in both sexes and at all developmental stages. HPLC-ELISA results revealed a number of immunoreactive components in H. glycines preparations, and a comparison with extracts of the free-living nematodes Caenorhabditis elegans and Panagrellus redivivus showed significant qualitative differences in FaRP immunoreactivity between the plant parasite and the two free-living nematodes. Total and specific immunoreactivities varied during H. glycines development, with the highest specific activity in juveniles and males, and the highest total activity in mature females. Total female immunoreactivity was located primarily within the mature eggs. A significant portion, however, was associated with the female body, perhaps with egg laying.