abdelmageed, haggag , Attaya, Hosam , Fokar, Mohamed , Allen, Randy D. .
Characterization of the Brassinosteroid-Specific Regulatory Factor BZR1 in Cotton Fiber Development.
Brassinosteroids (BR) are a family of phytosterols that act as growth regulators in plants. These molecules are active at micromolar concentrations and regulate a variety of plant processes including cellular elongation, seed germination, vascular development and photomorphogenesis. We have shown that application of BR to cultured cotton ovules increased fiber growth while exposure to the BR biosynthesis inhibitor Brassinazole (BRZ) inhibited fiber initiation and elongation. Using information from the plant model Arabidopsis to search for specific components of the BR signal transduction pathway in cotton, we identified an ortholog of BZR1 (GhBZR) that is expressed during cotton fiber development. Members of the BZR1/BES1 family constitute a novel group of plant transcription factors that act synergistically to mediate both transcriptional activation and suppression functions associated with BR signaling. The cotton BZR1 is closely related to BZR1/BES1 from Arabidopsis (>70% amino acid sequence identity). The GhBZR is ubiquitously expressed during fibers development. Wild type Arabidopsis plants expressing the Ghbzr1 show no phenotype, while the expression of the dominant negative form of bzr1-1D show a phenotype suggestive of BR hypersensitivity. Expression of the bzr1-1D in the BR insensitive bri1-5 Arabidopsis plants resulted in a complete phenotypic rescue. In addition, co-infiltration experiments show that GhBZR1 activated a GUS reporter gene with an XET promoter but did not suppress GUS expression under control of the CPD promoter. These results suggest that the GhBZR1 is likely to be BES1 ortholog. Experiments are in progress to determine the levels of BR-responsive gene expression in plants that over-express GhBZR1.
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1 - Texas Tech University, Biological Sciences, Lubbock, TX, 79409, USA
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM