Polypyrimidine tract-binding (PTB) proteins are RNA-binding proteins that target specific RNAs for post-transcriptional processing by binding CU-rich motifs. PTBs have established functions in a range of RNA processes including splicing, translation, stability, and long-distance transport. Six PTB-like genes identified in potato have been grouped into two clades based on homology to other known plant PTBs. StPTB1 and StPTB6 are closely related to a PTB protein discovered in pumpkin, designated CmRBP50, and contain four canonical RNA-recognition motifs. CmRBP50 is expressed in phloem tissues and functions as the core protein of a phloem-mobile RNA/protein complex. Sequence from the potato genome database was used to clone the upstream sequence of these two genes and was analyzed to identify conserved cis-elements. Whereas a number of elements were identified, the promoter of StPTB6 was enriched with regulatory elements for light induction and defense. Cloned promoter fragments were fused to β-glucuronidase and monitored in transgenic potato lines. The expression of each gene was complementary in most tissues analyzed with StPTB1 expression exclusively in the phloem and StPTB6 in ground tissues including leaf mesophyll. Limited overlapping expression was observed in root phloem and stolons and tubers where StPTB6 was induced during early stages of tuberization and in response to sucrose. Sequence from StPTB6 contained sucrose and tuber-specific elements similar to those observed in the promoters of major tuber storage proteins, patatin and proteinase inhibitor II. These results suggest that expression of CmRBP50-like proteins of potato is tissue-specific and linked to both developmental and environmental cues.
|Advisor:||Hannapel, David J.|
|Commitee:||Becraft, Philip W., Fei, Shui-zhang|
|School:||Iowa State University|
|School Location:||United States -- Iowa|
|Source:||MAI 50/06M, Masters Abstracts International|
|Subjects:||Molecular biology, Plant biology|
|Keywords:||Gus, Long-distance signaling, Phloem-specific, Ptb, Tssr, Tuberization|
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