Characterization of an oxidative burst signaling pathway leading to induction of the early nodulin rip1 in Medicago truncatula /
Legume plants mount a complex array of diverse responses to compatible Rhizobium and its signal molecule the Nod factor. Information that resides in the Nod factor structure specifically triggers the activation of several plant genes in legumes that are collectively referred to as nodules. Of known...
| Main Author: | |
|---|---|
| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1999.
|
| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731681421&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Legume plants mount a complex array of diverse responses to compatible Rhizobium and its signal molecule the Nod factor. Information that resides in the Nod factor structure specifically triggers the activation of several plant genes in legumes that are collectively referred to as nodules. Of known nodulins, rip1 remains the earliest known nodular that is abundantly expressed during early stages of symbiosis. rip1, which encodes a putative peroxidase protein, is induced by Rhizobium and purified Nod factor in the differentiating root epidermis and in nascent nodule primordia (Cook et al., 1995; Peng et a1., 1996). The focus of the present study has been to investigate the signal transduction pathway leading from Nod factor perception to the transcriptional activation of rip1. Analysis of putative cis-elements in the rip1 promoter revealed ocs-like (octopine synthase) and obp-like (ocs binding proteins) motifs that are frequently associated with promoters of plant genes that respond to reactive oxygen species. To test the hypothesis that an oxidative burst is involved in rip1 induction, we have examined rip1 expression in response to exogenous hydrogen peroxide. We have also used agonists and antagonists of eukaryotic oxidative burst signaling pathways to test the correlation between Nod factor perception, the oxidative burst, and rip1 transcription. The results of these studies indicate that exogenous hydrogen peroxide is sufficient to stimulate rip1 expression, while inhibitors of endogenous hydrogen peroxide production block rip1 induction. Moreover, application of Nod factor to Medicago truncatula roots rapidly stimulates an oxidative burst in the root zone that is susceptible to modulation. The data suggest that the Nod factor-induced oxidative burst is characterized by the generation of superoxide (O[]) and its subsequent conversion to hydrogen peroxide (H[]O[]). Using a series of Rhizobium mutants producing different Nod factor structures, and a plant mutant defective for symbiosis, we have established a functional link between Nod factor structure, elicitation of oxidative burst, plant gene function and transcriptional activation of rip1. Our results also suggest that H[]O[] generated via oxidative burst is an important intermediary signal controlling pathways leading to induction of the downstream nodulins enod12 and enod40. |
|---|---|
| Item Description: | Vita. "Major Subject: Plant Pathology". In title numerals are used. |
| Physical Description: | x, 103 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 89-102). |