The nervous system of plant-parasitic nematodes and their behaviors

Nematodes are the most abundant animals on earth. The majority of nematodes are free-living which feed on bacteria and fungi in the soil. However, some nematodes are parasitic to other animals and plants and have a huge impact on human health and agriculture worldwide. The nervous system of the non-parasitic nematode Caenorhabditis elegans has been studied extensively. Based on C. elegans and a few other species, nematode nervous systems were thought to be highly conserved. However, using a comparative neuroanatomy approach, I found unexpected variation in the number and structural properties of neurons among ten species across four clades. To further study the nervous system of plant-parasitic nematodes, I investigated how the neurotransmitter serotonin regulates their behaviors. Neurotransmitters are endogenous molecules used by neurons for signal transmission. Serotonin regulates feeding and reproductive behaviors in C. elegans, but its role in plant-parasitic nematodes remains unknown. In the root-lesion nematode Pratylenchus penetrans, I detected serotonergic neurons in cells adjacent to feeding and reproductive structures. I observed that exogenous serotonin induced P. penetrans feeding and reproductive behaviors. Also, using pharmaceutical compounds that disrupt serotonin signaling, my data suggest that these neurons regulate feeding and reproductive behaviors through endogenous serotonin. The soybean cyst nematode Heterodera glycines has a distinct life cycle: both juvenile males and females lose their mobility when feeding is initiated; however, the adult males regain their mobility while females never regain mobility. As a part of a collaborative study with other lab members, I have studied the change in the mobility of H. glycines from a neuronal aspect. GABA is the most prominent inhibitory neurotransmitter in nematodes. I have constructed a map of GABAergic neurons and cloned the gene encoding the key enzyme in GABA synthesis (hg-unc-25) in H. glycines. I have used heterologous rescue in a Caenorhabditis elegans mutant and validated that HG-UNC-25 is indeed the GABA synthesizing enzyme in H. glycines. Also, I have found the sedentary stages of H. glycines is associated with a reduction of GABAergic neurons in the ventral nerve cord. Together, my research has provided evidence that the nervous systems of nematodes are not as conserved as we thought and there is a need to further investigate the nervous system. A better understanding of the nervous system of plant-parasitic nematodes may be important to understand the evolution of these parasitic nematodes. More importantly, the knowledge of the how the nervous system regulates the specific behaviors of plant-parasitic nematodes may provide insights into new control strategies.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Han, Ziduan

Contributors dc:contributor

• Schroeder, Nathan E.
• Lambert, Kris N.
• Domier, Les
• Diers, Brian W.

• invertebrate
• amphid
• ventral nerve cord
• GABA
• stylet
• neuromuscular
• C. elegans
• neurotransmitter
• unc-25

Statement dc:rights

• Copyright 2018 Ziduan Han

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/101006

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/101006