Molecular biology of salt tolerance in the facultative halophyte Mesembryanthemum crystallinum: Identification and regulation of stress-responsive mRNAs.

Persistent Link:
http://hdl.handle.net/10150/185921
Title:
Molecular biology of salt tolerance in the facultative halophyte Mesembryanthemum crystallinum: Identification and regulation of stress-responsive mRNAs.
Author:
Vernon, Daniel Marc.
Issue Date:
1992
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
As sessile organisms, plants are subject to numerous environmental insults. Of these, salinity is one of the most widespread and important in terms of limiting plant distribution and productivity. Molecular studies have established that plants challenged by high salinity respond by increasing expression of specific genes. A functional role for the products of such genes in stress tolerance has not been established, however, and little is known about the biochemical mechanisms that allow plants to tolerate osmotic stress. Mesembryanthemum crystallinum is a facultative halophyte capable of adjusting to and surviving in highly saline conditions. I have generated and screened a subtracted cDNA library to identify mRNAs that accumulate during this plant's adaptation to salt stress. Three mRNAs were identified that increased in abundance in leaf tissue of salt stressed plants. Patterns of induction for these mRNAs differed. The most dramatically-induced mRNA, Imt1, was characterized in depth. Imt1 expression was induced in leaves and, transiently, in roots. Nuclear run-on assays indicated that the gene is transcriptionally regulated. In several respects, the expression of Imt1 differed from that of other salinity-responsive genes involved in photosynthetic metabolism in M. crystallinum: The mRNA was induced by salinity and low temperature, but not by drought, and its induction by stress was not influenced by plant age. Imt1 encoded a predicted polypeptide of Mr 40,250 which exhibited sequence similarity to several hydroxymethyl transferases. The IMT1 protein was expressed in E. coli and identified by functional assay as a myo-inositol methyl transferase that catalyzes the first step in the biosynthesis of the cyclic sugar alcohol pinitol. The presence of high levels of sugar alcohols has been correlated with osmotolerance in a wide range of organisms, and the stress-initiated transcriptional induction of IMT1 expression in a facultative halophyte provides the strongest support to date for the importance of sugar alcohols in establishing tolerance to osmotic stress in higher plants. The ability of this methyl transferase to generate a putative osmoprotectant from a ubiquitous plant substrate makes it an attractive candidate enzyme for the creation of stress-resistant transgenic plants.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Ice plant.; Soils, Salts on.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Molecular and Cellular Biology; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Bohnert, Hans J.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleMolecular biology of salt tolerance in the facultative halophyte Mesembryanthemum crystallinum: Identification and regulation of stress-responsive mRNAs.en_US
dc.creatorVernon, Daniel Marc.en_US
dc.contributor.authorVernon, Daniel Marc.en_US
dc.date.issued1992en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractAs sessile organisms, plants are subject to numerous environmental insults. Of these, salinity is one of the most widespread and important in terms of limiting plant distribution and productivity. Molecular studies have established that plants challenged by high salinity respond by increasing expression of specific genes. A functional role for the products of such genes in stress tolerance has not been established, however, and little is known about the biochemical mechanisms that allow plants to tolerate osmotic stress. Mesembryanthemum crystallinum is a facultative halophyte capable of adjusting to and surviving in highly saline conditions. I have generated and screened a subtracted cDNA library to identify mRNAs that accumulate during this plant's adaptation to salt stress. Three mRNAs were identified that increased in abundance in leaf tissue of salt stressed plants. Patterns of induction for these mRNAs differed. The most dramatically-induced mRNA, Imt1, was characterized in depth. Imt1 expression was induced in leaves and, transiently, in roots. Nuclear run-on assays indicated that the gene is transcriptionally regulated. In several respects, the expression of Imt1 differed from that of other salinity-responsive genes involved in photosynthetic metabolism in M. crystallinum: The mRNA was induced by salinity and low temperature, but not by drought, and its induction by stress was not influenced by plant age. Imt1 encoded a predicted polypeptide of Mr 40,250 which exhibited sequence similarity to several hydroxymethyl transferases. The IMT1 protein was expressed in E. coli and identified by functional assay as a myo-inositol methyl transferase that catalyzes the first step in the biosynthesis of the cyclic sugar alcohol pinitol. The presence of high levels of sugar alcohols has been correlated with osmotolerance in a wide range of organisms, and the stress-initiated transcriptional induction of IMT1 expression in a facultative halophyte provides the strongest support to date for the importance of sugar alcohols in establishing tolerance to osmotic stress in higher plants. The ability of this methyl transferase to generate a putative osmoprotectant from a ubiquitous plant substrate makes it an attractive candidate enzyme for the creation of stress-resistant transgenic plants.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectIce plant.en_US
dc.subjectSoils, Salts on.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineMolecular and Cellular Biologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairBohnert, Hans J.-
dc.contributor.committeememberMiesfeld, Rogeren_US
dc.contributor.committeememberVierling, Elizabethen_US
dc.contributor.committeememberOishi, Karen-
dc.identifier.proquest9238526en_US
dc.identifier.oclc700943225en_US
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