P-proteins are structurally distinct proteins present in the sieve element-companion cell complexes of phloem tissue. Genomic clones encoding the two major P-proteins, the phloem filament protein (PP1) and the phloem lectin (PP2), were isolated and characterized. To understand mechanisms that control phloem-specific expression of these two genes, approximately 1 kb of the 5' flanking region from PP1 and PP2 genomic clones were fused with the GUS reporter gene and introduced into tobacco plants using Agrobacterium tumefaciens-mediated gene transfer. For both promoters, histochemical staining detected GUS activity specifically in the phloem tissue that was most easily detected in stems followed by midrib, secondary veins, roots, and leaf lamina of transgenic tobacco plants. GUS activity directed by the PP2 promoter was approximately 23 times greater than GUS activity directed by the PPI promoter. A nested set of 5' deletions between nucleotides -1014 and +32 were constructed to localize cis-elements that specify the patterns of PP2 gene expression in the phloem. Deletions within this region revealed that nucleotides -228 to +32 relative to the transcription initiation site contained sufficient information to direct phloem-specific gene expression, while positive regulators of promoter activity appeared to be located upstream of nucleotide -621. Mutation of a conserved 13-bp sequence, TTAAAAGAAGATA, found in the minimal PP2 promoter did not affect reporter gene expression. Sucrose responsive elements were identified in the PP2 promoter that could contribute to increased promoter activity in response to sugar. Finally we initiated studies to construct a phloem-specific promoter that could be induced by wound released compounds such as ethylene. Although not conclusive, our results suggest that it is possible to enhance phloem-specific expression in response to ethylene.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/298810 |
| Date | January 1998 |
| Creators | Carneiro, Andrea Almeida |
| Contributors | Thompson, Gary A. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| 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. |
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