A Synthetic Peptide Shows Retro- and Anterograde Neuronal Transport before Disrupting the Chemosensation of Plant-Pathogenic Nematodes

Dong Wang,Peter E Urwin,Howard J Atkinson,Laura M Jones,Guy Smagghe

doi:10.1371/journal.pone.0017475

Abstract

Cyst nematodes are a group of plant pathogens each with a defined host range that cause major losses to crops including potato, soybean and sugar beet. The infective mobile stage hatches from dormant eggs and moves a short distance through the soil to plant roots, which it then invades. A novel strategy for control has recently been proposed in which the plant is able to secrete a peptide which disorientates the infective stage and prevents invasion of the pathogen. This study provides indirect evidence to support the mechanism by which one such peptide disrupts chemosensory function in nematodes. The peptide is a disulphide-constrained 7-mer with the amino acid sequence CTTMHPRLC that binds to nicotinic acetylcholine receptors. A fluorescently tagged version of this peptide with both epifluorescent and confocal microscopy was used to demonstrate that retrograde transport occurs from an aqueous environment along bare-ending primary cilia of chemoreceptive sensilla. The peptide is transported to the cell bodies of these neurons and on to a limited number of other neurons to which they connect. It appears to be localised in both neuronal processes and organelles adjacent to nuclei of some neurons suggesting it could be transported through the Golgi apparatus. The peptide takes 2.5 h to reach the neuronal cell bodies. Comparative studies established that similar but less abundant uptake occurs for Caenorhabditis elegans along its well studied dye-filling chemoreceptive neurons. Incubation in peptide solution or root-exudate from transgenic plants that secrete the peptide disrupted normal orientation of infective cyst nematodes to host root diffusate. The peptide probably undergoes transport along the dye-filling non-cholinergic chemoreceptive neurons to their synapses where it is taken up by the interneurons to which they connect. Coordinated responses to chemoreception are disrupted when the sub-set of cholinergic interneurons secrete the peptide at synapses that have post-synaptic nicotinic acetylcholine receptors.

Highlights

Plant parasitic nematodes are major pathogens of plants that cause annual total cost of over $125 b to world crops [1] and are difficult to control
Exposure of J2 Heterodera schachtii to 1 mM fluorescein isothiocyanate (FITC) for 16 h resulted in dye-filling of certain amphidial neurons as in previous work [2]
The fluorescence of FITC is evident from the region of the amphids along the tract of at least some amphidial neuron dendrites to their cell bodies and forward along their short axons to the nerve ring (Fig. 1a)

Summary

Introduction

Plant parasitic nematodes are major pathogens of plants that cause annual total cost of over $125 b to world crops [1] and are difficult to control. The specific disruption of chemoreception of Heterodera and a second cyst nematode (Globodera pallida) was achieved by a peptide mimetic of aldicarb obtained by phage display. It binds to and inhibits acetylcholinesterase, and can be displaced from the enzyme by aldicarb. A second chemoreception-disrupting peptide (nAChRbp) was obtained by biopanning against a membrane fraction of Caenorhabditis elegans that was rich in nicotinic acetylcholine receptors (nAChR). The ability of the two peptides to disrupt chemoreception is of interest as both aldicarb and levamisole target cholinergic synapses by interfering with, respectively, enzymatic cleavage of the neurotransmitter acetylcholine and nicotinic acetylcholine receptors.

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