Genomes of parasitic nematodes (Meloidogyne hapla, Meloidogyne incognita, Ascaris suum and Brugia malayi) have a reduced complement of small RNA interference pathway genes: knockdown can reduce host infectivity of M. incognita

Localization and RNA Interference-Driven Inhibition of a Brugia malayi-Encoded Interleukin-5 Receptor Binding Protein

A molecule we termed Brugia malayi IL-5 receptor (IL-5R) binding protein (BmIL5Rbp; also known as Bm8757) was identified from B. malayi filarial worms and found to inhibit human interleukin-5 (IL-5) binding to its human receptor competitively. After the expression and purification of a recombinant BmIL5Rbp and generation of BmIL5Rbp-specific rabbit antibody, we localized the molecule on B. malayi worms through immunohistochemistry and immunoelectron microscopy. RNA interference (RNAi) was used to inhibit BmIL5Rbp mRNA and protein production. BmIL5Rbp was shown to localize to the cuticle of Brugia malayi and to be released in its excretory/secretory products. RNAi inhibited BmIL5Rbp mRNA production by 33%, reduced the surface protein expression by ~50%, and suppressed the release of BmIL5Rbp in the excretory/secretory products. RNAi has been used successfully to knock down the mRNA and protein expression of BmIL5Rbp in the early larval stages of B. malayi and provided a proof of principle for the local inhibition of the human IL-5R. These findings provide evidence that a parasite-encoded IL-5R antagonist may locally inhibit a vital host innate immune activation of IL-5 on eosinophils.

RNA interference of an orthologue of Dicer of Meloidogyne incognita alludes to the gene's importance in nematode development

Dicers and dicer-like enzymes play an essential role in small RNA processing in eukaryotes. Nematodes are thought to encode one dicer, DCR-1; only that for Caenorhabditis spp. is well-characterised. Using genomic sequences of eight root-knot nematodes (Meloidogyne spp.), we identified putative coding sequences typical of eukaryotic DICERS. We noted that the primary and secondary structures of DICERS they encode were different for different Meloidogyne species and even for isolates of the same species, suggesting paralogy for the gene. One of the genes for M. incognita (Midcr-1.1) expressed in eggs, juvenile stage 2 and adults, with the highest expression in the adult females. All the Meloidogyne DICERS had seven major domains typical of those for Caenorhabditis spp. and humans with very similar protein folding. RNAi of Midcr-1.1 in J2s using seven dsRNAs, each based on sequences encoding the domains, induced mild paralysis but measurable knockdown was detected in J2s treated with five of the dsRNAs. For four of the dsRNAs, the RNAi effect lasted and reduced the nematode’s infectivity. Also, host plant delivery of dsRNAs complementary to coding sequences of the Dicer Dimerisation domain impaired development, reducing nematode infection by 71%. These results confirm the importance of the gene to nematode health.

Attempt to Silence Genes of the RNAi Pathways of the Root-Knot Nematode, Meloidogyne incognita Results in Diverse Responses Including Increase and No Change in Expression of Some Genes

Control of plant-parasitic nematodes (PPNs) via host-induced gene silencing (HIGS) involves rational selection of genes and detailed assessment of effects of a possible knockdown on the nematode. Some genes by nature may be very important for the survival of the nematode that knockdown may be resisted. Possible silencing and effects of 20 such genes involved in the RNA interference (RNAi) pathways of Meloidogyne incognita were investigated in this study using long double-stranded RNAs (dsRNAs) as triggers. Two of the genes, ego-1 and mes-2, could not be knocked down. Expression of six genes (xpo-1, pash-1, xpo-2, rha-1, ekl-4, and csr-1) were significantly upregulated after RNAi treatment whereas for 12 of the genes, significant knockdown was achieved and with the exception of mes-2 and mes-6, RNAi was accompanied by defective phenotypes in treated nematodes including various degrees of paralysis and abnormal behaviors and movement such as curling, extreme wavy movements, and twitching. These abnormalities resulted in up to 75% reduction in infectivity of a tomato host, the most affected being the J2s previously treated with dsRNA of the gfl-1 gene. For 10 of the genes, effects of silencing in the J2s persisted as the adult females isolated from galls were under-developed, elongated, and transparent compared to the normal saccate, white adult females. Following RNAi of ego-1, smg-2, smg-6, and eri-1, reduced expression and/or the immediate visible effects on the J2s were not permanent as the nematodes infected and developed normally in tomato hosts. Equally intriguing was the results of RNAi of the mes-2 gene where the insignificant change in gene expression and behavior of treated J2s did not mean the nematodes were not affected as they were less effective in infecting host plants. Attempt to silence drsh-1, mut-7, drh-3, rha-1, pash-1, and vig-1 through HIGS led to reduction in nematode infestation by up to 89%. Our results show that genes may respond to RNAi knockdown differently so an exhaustive assessment of target genes as targets for nematode control via RNAi is imperative.

Effective approaches to study the plant-root knot nematode interaction

Plant-parasitic nematodes cause major agricultural losses worldwide. Examining the molecular mechanisms underlying plant-nematode interactions and how plants respond to different invading pathogens is attracting major attention to reduce the expanding gap between agricultural production and the needs of the growing world population. This review summarizes the most recent developments in plant-nematode interactions and the diverse approaches used to improve plant resistance against root knot nematode (RKN). We will emphasize the recent rapid advances in genome sequencing technologies, small interfering RNA techniques (RNAi) and targeted genome editing which are contributing to the significant progress in understanding the plant-nematode interaction mechanisms. Also, molecular approaches to improve plant resistance against nematodes are considered.