Characterization and regulation of the early nodulin gene rip1 in Medicago truncatula /
Primary induction of the Rhizobium-induced peroxidase gene
| Main Author: | |
|---|---|
| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1997.
|
| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=736824761&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Primary induction of the Rhizobium-induced peroxidase gene rip1 occurs prior to infection and nodule morphogenesis in Medicago truncatula (Cook et al., 1995) and expression of rip1 in root tips is correlated with competence of this zone for modulation (Peng et al., 1996). rip1 transcripts are characterized by a single major transcription initiation site, three exons, two introns and multiple polyadenylation sites distributed within 200 to 400 bp of the proposed translation stop site. By means of Southern blot analysis, we determined that sequences within the rip1 promoter are highly methylated in DNA from both leaves and roots. Coincident with the region of DNA methylation, we identified a 377-bp transposon-like (TL) element that is widely distributed in the M. truncatula genome. Characterization of five closely related M. truncatula TL elements revealed that the inverted terminal repeats of these elements are highly conserved, while limited homology was evident within the intervening region. The structure of these elements is reminiscent of retrotransposons because they contain sequence homology to proteins typically encoded by retrotransposons or retroviruses such as the gag, pol and env genes. Transient assay of rip1-reporter gene fusions by biolistic bombardment revealed regulatory effects of both 5' and 3' flanking sequences. Complete deletion of the rip1 TL-element resulted in a 2-fold increase in expression of reporter genes, while partial deletion of the 3' inverted terminal repeat caused decreased levels of reporter gene activity. These results suggest that the rip1 TL element may play a role in regulating rip1 expression. The rip1 3' untranslated region (UTR) was shown to exert negative effect on reporter gene expression relative to the CaMV 35S 3' region. Suspected negative cis-regulatory elements (i.e. putative message instability elements) were identified within the rip1 3'UTR, however, transient assay of site-directed mutants was unable to identify a role for these sequence motifs in rip1 regulation. |
|---|---|
| Item Description: | Vita. "Major Subject: Plant Pathology". |
| Physical Description: | x, 175 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 156-173. |