<p>Reactive oxygen species (ROS) are known to act as both signaling molecules and direct antimicrobial agents in plant defense against pathogens. Many plant pathogens have the ability to synthesize mannitol, a potent ROS quencher, and there is growing evidence that at least some phytopathogenic fungi use mannitol to suppress ROS mediated defenses. Here we show that mannitol production and secretion in the phytopathogenic fungus, Alternaria alternata is induced in the presence of host plant extracts. Additionally we demonstrate that the catabolic enzyme mannitol dehydrogenase (MTD) is induced in a non-mannitol-producing plant in response to both fungal elicitor and specific inducers of plant defense responses. This indicates a mechanism whereby the plant can counteract fungal suppression of ROS-mediated defenses by catabolizing mannitol of fungal origin. To further clarify this interaction, tobacco plants were transformed with celery mannitol dehydrogenase cDNA under a constitutive promoter, resulting in an enzymatically active MTD protein. This constitutive MTD expression conferred enhanced resistance to A. alternata, and this resistance did not correlate with expression of PR1a, a protein often used as an indicator of systemic acquired resistance. Constitutive Mtd expression did not enhance tolerance to two non-mannitol secreting pathogens, the fungal pathogen Cercospora nicotianae and the bacterial pathogen Pseudomonas syringae pv. tabaci. These results are consistent with the hypothesis that MTD plays a role in plant resistance to mannitol secreting fungal pathogens by catabolizing mannitol of fungal origin. <P>
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-20001102-175638 |
| Date | 05 February 2001 |
| Creators | Jennings, Dianne Brooks |
| Contributors | John Williamson, D. Mason Pharr, Margaret Daub, Steve Clouse |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-20001102-175638 |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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