Profiling Root Knot Nematode-Tomato Interactions

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Title: Profiling Root Knot Nematode-Tomato Interactions
Author: Schaff, Jennifer Evelyn
Advisors: Dr. Greg C Gibson, Committee Member
Dr. Steven A Lommel, Committee Member
Dr. David McK Bird, Committee Chair
Dr. Dahlia M Nielsen, Committee Member
Abstract: Root-knot nematodes (RKN) have a very broad host range, encompassing over 2,000 plant species and most agricultural crops are parasitized by at least one species of Meloidogyne, causing billions of dollars in crop yield loss worldwide and chemical contamination of the environment through judicious use of nematicides. RKN elicit dramatic morphological changes in susceptible plants to establish obligatory feeding sites that consist of metabolically active, multinucleate giant cells. Giant cells are remarkably similar in very different plant species suggesting signals from the nematode interact with fundamental aspects of plant cell biology and differentiation. I am interested in the concomitant global changes of host and nematode gene expression during RKN pathogenesis. I initiated a microarray experiment using a unique, defined set of tomato genes known to be expressed in tomato root tissue. Microarrays were interrogated with infected resistant tissue and infected susceptible tissue collected over four time points representing subsequent stages of RKN infection and I generated and applied a sophisticated looped and interwoven looped designed to facilitate comparison of all these tissues. This is the first time that a microarray analysis has been employed to establish host responses to nematodes in a natural host, and is first time transcript abundance comparisons have been made in the very early time frame following infection and therefore gives the first comprehensive glimpse at gene expression during initiation of giant cells and during the resistant response. I found that expression patterns in a susceptible reaction fluctuate significantly around base-line, non-infected expression levels and expression of genes involved in the resistant response do not fluctuate, but stay regulated in the same direction (as compared to non-infected tissue) over the first three days post infection. One gene significantly up-regulated (at q<0.05) during a resistant response is a glycosyltransferase and was chosen for gene expression ablation experiments. I found that in absence of expression, nematodes are able to establish feeding sites in the plant indicating that this gene is part of the necessary resistance pathway in the plant. As well as exploring gene regulation during host response to RKN, I examined gene regulation in nematodes during pathogenesis. Nematode transcript analysis using microarrays has yet to be established and one reason may be that it is difficult to dissect nematodes from root tissue, especially during early hours post infection. I demonstrated that transcript and changes in transcripts can be detected using RNA extracted from infected root tissue, alleviating the need to dissect out the nematodes. In addition to the microarray analyses, I have analyzed, annotated, and profiled the expression of the giant cell library first constructed in 1994. The results reported here validate the gene discovery from this library, and expand our knowledge of both host and nematode genes regulated during a sophisticated parasitic interaction. The study of plant development and cell biology is of critical importance for the continued improvement of crop species and can lead to broad improvements in plant breeding programs, yield improvement, and general stress management.
Date: 2007-03-08
Degree: PhD
Discipline: Plant Pathology

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