Rhizobial-Legume Symbiosis and Root Knot Nematode Parasitism: Common Signal Transduction Pathways in Legumes

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Title: Rhizobial-Legume Symbiosis and Root Knot Nematode Parasitism: Common Signal Transduction Pathways in Legumes
Author: Weerasinghe, Ravisha Risanthi
Advisors: Ross Whetten, Committee Member
David McKenzie Bird, Committee Co-Chair
Wendy F Boss, Committee Member
Nina Strömgren Allen, Committee Co-Chair
Abstract: Nodulation is an ecologically and economically important plant phenomenon, in which the symbiosis between plants from the family Fabaceae and the bacterial genera rhizobia results in the development of nitrogen fixing nodules on host plant roots. The rhizobia-plant interaction is initiated by Nod factors, which are produced by species-specific rhizobia; Nod factor alone is necessary and sufficient to produce many of the initial responses including ionic fluxes, root hair deformation, changes in gene expression, cortical cell differentiation and generation of a pseudo nodule. Giant cell formation by plant pathogenic root knot nematodes (RKN) invokes host genes necessary for nitrogen-nodule formation. Specific transcription regulators, cytokinin response pathways and early nodulation genes are induced in the nematode feeding site and rhizobia induced nodules. This suggests that nodulation by rhizobia and RKN infection may share host signal transduction and/or developmental pathways. The presence of horizontally acquired nodulin (bacterial genes encoding Nod factors) genes in Meloidogyne incognita is consistent with this concept and indicates that RKN might produce functionally equivalent signaling molecules capable of inducing similar downstream events. Since cytoskeleton involvement during rhizobia-legume symbiosis and nematode infection is largely unknown, the objectives of this thesis were to observe microtubule changes during nodulation and to compare the cytoskeletal behavior of legumes during both Nod factor signal transduction and RKN infection. This thesis demonstrates that rhizobial Nod factors are in some ways similar to signals that are generated by plant parasitic RKN. The RKN signal molecules appear to share common receptors and induce rapid cytoskeletal (both microtubules and actin) and morphological changes in root hairs, to those that are generated by rhizobial Nod factors. GFP labeling of the cytoskeleton demonstrated that the initiation of giant cells occurs without RKN attaching to the site of induction. Hence RKN signals function at a distance. The demonstrated common aspects between nematode parasitism and rhizobial nodulation will play a key role in our understanding of these economically important relationships.
Date: 2004-07-13
Degree: PhD
Discipline: Botany
URI: http://www.lib.ncsu.edu/resolver/1840.16/4700

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