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Eric L. Davis
Williams Neals Reynolds Distinguished ProfessorCampus Box 7903 Office: (919) 515-6692 NCSU Biotechnology Faculty MemberNCSU Research and Professional Ethics Program FellowTeaching ActivitiesPP790C-Phytonematology (formerly PP504)Pre: PP 315 or Consent of Instructor . I am the instructor for this introductory course in nematology. Nematodes are microscopic worms (often less than 1mm long) that are soil-dwelling, and they mainly attack plant roots. PP 504 is a 3-credit, graduate-level class with lab held in the Spring semester of odd numbered years. The course is designed for students with a background in plant pathology, biology, or agricultural sciences, and no prior experience in plant pathology or nematology is required (PP 315 is preferred). Graduate students in majors related to plant pathology are welcome, and PP 504 is open to upper-level undergraduate students with consent of the instructor. Strong emphasis is placed on the integration of classical nematology with modern approaches, and the laboratory portion of PP504 contains lessons from nematode identification to molecular biology. Research InterestsOur lab's primary interest is with plant-parasitic nematodes, but we are also interested in all aspects of host-parasite interactions. The main objective of our research is to combine information that we generate in both basic and applied investigations towards the goal of improving the control of plant-parasitic nematodes in agriculture. Our present research projects involve:
The majority of our research centers around the soybean cyst nematode (SCN), Heterodera glycines, the tobacco cyst nematode (TCN), Globodera tabacum, and the root-knot nematodes, Meloidogyne spp. Cyst nematodes have a very narrow plant host range, while root-knot nematodes have a very wide plant host range. Both types of nematodes enter plant roots completely and transform selected plant cells into elaborate feeding sites that act as permanent nutrient sinks for the rest of the nematode’s sedentary life cycle. Cyst and root-knot nematodes cause billions of dollars in damage each year to many different crops world-wide, and environmentally-safe means of their control are in great demand. We study the parasitism proteins (secretions) from cyst nematodes and root-knot nematodes that are critical in the plant infection process, and we employ protein and genomics-based approaches to isolate the "parasitism genes" (Davis et al. 2000) encoding these molecular signals. We are conducting experiments using immunocytochemistry and advanced microscopy to monitor nematode secretions and cellular changes within plant roots infected by nematodes. The ultimate objective of this research is to bioengineer plants to disrupt the infection process and make the plants resistant to nematodes. We collaborate closely on many projects with selected U.S and international scientists to form an International Molecular Plant-Nematode Interactions Group including T.J. Baum of Iowa State University, R.S. Hussey of the University of Georgia, Melissa G. Mitchum of the University of Missouri, Xiaohong Wang of Cornell University, Marie Noelle Rosso of INRA, France, and Geert Smant of Wageningen University, The Netherlands. Secretions Encoded by Phytonematode Parasitism GenesProtein ApproachA primary objective of our research is to identify the components and functions of plant-parasitic nematode secretions, with an ultimate goal of targeted disruption of the parasitic process. Parasitism proteins secreted from the nematode stylet (Davis et al., 2004]) play pivotal roles in the infection process. The stylet secretions are produced within the two subventral (SvG) and single dorsal (DG) esophageal gland cells of the nematode, and the activity and contents of these gland cells are dynamic throughout the parasitic cycle. Our initial approach was at the protein level using antibodies that we developed to isolate secretory proteins. Most notable was the isolation of a subventral gland antigen whose amino acid sequence was used to clone the first cellulase (beta-1,4 endoglucanase) genes (Smant et al., 1998) from an animal (cyst nematode). Secretion of the cellulases during nematode migration through root tissues was confirmed (Wang et al. 1999), and analyses of the cellulase genes provided the first reports of potential horizontal gene transfer from bacteria to nematodes (Yan et al., 1998). Genomics ApproachcDNA libraries generated by RT-PCR from mRNA in the microaspirated contents of soybean cyst and root-knot nematode esophageal gland cells at various parasitic stages were either subjected to selection strategies or chosen for direct expressed sequence tag (EST) analyses (Gao et al., 2003; Huang et al., 2003; Wang et al., 2001). For soybean cyst and root-knot nematodes, respectively, greater than fifty and thirty unique "parasitism gene" clones demonstrating a predicted N-terminal signal peptide for secretion and expression exclusively in the esophageal gland cells (SvG and/or DG) by mRNA in situ hybridization have been generated and prioritized. Microarrays spotted with cDNA of the parasitism genes isolated from soybean cyst nematode indicated differential expression of these genes in early and late nematode parasitic stages (DeBoer et al., 2002). Parasitism Gene FunctionPolyclonal antibodies generated to synthetic peptides derived from sequence of prioritized parasitism genes are being evaluated by Research Associate Dr. Hanane Diab The C-terminal domain of the H. glycines parasitism gene SYV46 (Wang et al., 2001) has similarity to CLAVATA3, an endogenous plant peptide locally secreted by specific meristem cells to control plant stem cell differentiation and negatively regulate the plant WUSCHEL gene. Former Research Associate Dr. Xiaohong Wang To test the potential binding of SYV46 to a CLV1 receptor, and to exploit the available Arabidopsis genetic resources to assay the function of other nematode parasitism genes, homologs of the H. glycines parasitism genes are being investigated by current PhD student Nrupali Patel A number of the secreted SCN parasitism gene products have a predicted nuclear localization signal (NLS). Expression of the NLS of some SCN parasitism genes fused to GUS & GFP localizes to the nucleus of plant cells (below) in transient expression assays by collaborators at Iowa State University (Axel Elling & Thomas Baum). We are also investigating gene knockout via RNA interference (RNAi) as an alternative functional analysis of nematode parasitism genes. Former Research Associate Dr. Serenella Sukno Plant Response to Nematode Parasitism We have been active in identifying and monitoring the activity of plant cell wall-modifying enzymes in nematode feeding cells. Former PhD student Melissa Goellner Mitchum As plant cellulases remodel feeding cell walls, extensive deposition of cell wall material results in thickened walls and numerous wall ingrowths. Current PhD student Laura Hudson Select Program Publications (Cited):
Program Funding
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and Lab Research Specialist Chunying Li
in our lab. The antisera will be used to detect where and when individual parasitism gene products are secreted in planta. 
has demonstrated that HG-SYV46 can complement a clv3 mutant of Arabidopsis and regulate WUSCHEL expression (
in the related beet cyst nematode (BCN), Heterodera schachtii. 
and current MS student Jamie McCuiston 
have demonstrated RNAi of a pectate lyase gene expressed exclusively in the SvG of SCN via ingestion of double-stranded RNA (dsRNA) from a soaking medium. Efforts are now underway to express dsRNA to SCN parasitism genes in planta for ingestion and potential RNAi effects on parasitism.
has identified several beta-1,4 endoglucanase (cellulase) genes upregulated in giant-cells and syncytia (
is now investigating the potential activity of plant cellulose synthase (CesA) in nematode feeding cells. In initial tests, Arabidopsis plants with mutations in specific CesA genes appear to inhibit root-knot infection.
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