FMRFamide-like peptides in root knot nematodes and their potential role in nematode physiology

Abstract

FMRFamide-like peptides (FLPs) are a diverse group of neuropeptides that are expressed abundantly in nematodes. They exert potent physiological effects on locomotory, feeding and reproductive musculature and also act as neuromodulators. However, little is known about the specific expression patterns and functions of individual peptides. The current study employed rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR) to characterize flp genes from infective juveniles of the root knot nematodes, Meloidogyne incognita and Meloidogyne minor. The peptides identified from these transcripts are sequelogs of FLPs from the free-living nematode, Caenorhabditis elegans; the genes have therefore been designated as Mi-flp-1, Mi-flp-7, Mi-flp-12, Mm-flp-12 and Mi-flp-14. Mi-flp-1 encodes five FLPs with the common C-terminal moiety, NFLRFamide. Mi-flp-7 encodes two copies of APLDRSALVRFamide and APLDRAAMVRFamide and one copy of APFDRSSMVRFamide. Mi-flp-12 and Mm-flp-12 encode the novel peptide KNNKFEFIRFamide (a longer version of RNKFEFIRFamide found in C. elegans). Mi-flp-14 encodes a single copy of KHEYLRFamide (commonly known as AF2 and regarded as the most abundant nematode FLP), and a single copy of the novel peptide KHEFVRFamide. These FLPs share a high degree of conservation between Meloidogyne species and nematodes from other clades, including those of humans and animals, perhaps suggesting a common neurophysiological role which may be exploited by novel drugs. FLP immunoreactivity was observed for the first time in Meloidogyne, in the circumpharyngeal nerve ring, pharyngeal nerves and ventral nerve cord. Additionally, in situ hybridization revealed Mi-flp-12 expression in an RIR-like neuron and Mi-flp-14 expression in SMB-like neurons, respectively. These localizations imply physiological roles for FLP-12 and FLP-14 peptides, including locomotion and sensory perception.

Combinatorial in vitro RNAi of two neuropeptide genes and a pharyngeal gland gene on Meloidogyne incognita

“…This resulted in almost complete inhibition of migration of the J2 in a sand column. Expression studies revealed expression of flp-14 gene in four SMB-like neurons posterior to the central nerve ring (Johnston et al, 2010). In C. elegans, the SMBs connect indirectly with amphid (sensory) and motor neurons suggesting their role in nematode movement and signal transduction.…”

“…In situ hybridisation allows the visualisation of the site of FLPencoding mRNA transcripts through the binding of highly specific labelled DNA probes (Kimber et al, 2002). Using this approach, flp-14, which encodes two copies of a single FMRFamide-related peptide in M. incognita, has been found to be expressed in inter-neurons and motorneurons associated with body wall muscle of the head region of the nematode (Johnston et al, 2010). On the other hand, flp-18 encodes five copies of FMRFamiderelated peptide in M. incognita and its site of expression is not known (Eisenmann, 2005).…”

Neurobiology of plant parasitic nematodes

“…A total of eleven peptides are encoded by these transcripts and examples are shown in Table 1, together with those from other studies, and compared with peptides from G. pallida and C. elegans. Immunocytochemical studies using an antibody against FMRFamide showed staining in the circumpharyngeal nerve ring, lateral ganglia and ventral nerve cord of J2 M. incognita (Johnston et al 2010). FLP immunoreactivity was observed in the pharyngeal nerves which project to the metacarpal bulb which controls pharyngeal pumping during feeding.…”

“…In situ hybridisation showed Mi-flp-12 expression in an RIR-like neuron and Mi-flp-14 expression in four SMB-like neurons of C. elegans. In C. elegans, SMB neurons synapse with amphid and motoneurons, which suggests that their peptides may have a role in sensory and motor function in M. incognita and other plant nematodes (Johnston et al 2010). In their paper, Johnston et al summarise the location of peptides encoded by flp-1, 7, 12 and 14 in M. incognita, G. pallida and C. elegans.…”

“…They concluded that flp genes are essential for the coordination of motor activity in G. pallida and so provide targets for new anthelmintics. Four flp transcripts, viz, Mi-flp-1, 7, 12 and 14, have been characterised from M. incognita using RACE-PCR (Johnston et al 2010). A flp-12 has also been characterised from M. minor, which has one copy of KNNKFEFIRFa.…”