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Abstract Detail


Hormone Biology

Desgagne-Penix, Isabel [1], Sponsel, Valerie [2].

Auxin status regulates the expression of the GA20ox1 gene in seedlings of Arabidopsis thaliana.

Auxin and Gibberellin (GAs) overlap in the regulation of many aspects of plant development. GA responses, such as growth, are tightly linked to GA biosynthesis by a feedback mechanism. GA 20-oxidase (GA20ox) catalyzes a rate-limiting step in the synthesis of bioactive GAs. The current model for GA signaling proposes that feedback regulation functions via the activity of DELLA protein repressors, where stabilization of these proteins by reduced GA levels or signaling results in the increased expression of GA20ox1. Previously, we showed that AtGA20ox1 expression was up-regulated in response to treatment with auxin transport inhibitors (ATIs). The up-regulation of AtGA20ox1 caused by ATIs could be mediated by a feedback mechanism, by an independent mechanism, or by a combination of both. We are investigating whether ATI effects on AtGA20ox1 are a consequence of feedback regulation or not. Using the DR5::GUS reporter gene, we showed that the auxin levels were altered following ATI treatments, and RT-PCR analysis showed that the expression of GA20ox1 was increased. However, the AtGA20ox1 up-regulation caused by ATIs can be reversed by combination treatment with GA. Our results suggests that the ATIs mediate their effect on AtGA20ox1 by reducing bioactive GA pools, which in turn up-regulates AtGA20ox1 by a feedback mechanism. The effects of ATIs on GA levels also support the idea that effects on GA metabolism mediate part of auxin responses. The mechanism(s) by which auxin status affects AtGA20ox1 expression are still under investigation. We postulate that the GA/auxin interactions are complex but might comprise mechanisms of loops and feedback regulations affecting each others metabolic and signaling pathways. Work supported by the MBRS-RISE GM60655 and the NSF 0080934.


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1 - University of Texas at San Antonio, Department of Biology, 6900 N Loop 1604 W, San Antonio, Texas, 78249, USA
2 - University of Texas at San Antonio, Biology

Keywords:
gibberellin
auxin
GA20ox
Auxin transport
DELLA.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P35030
Abstract ID:896


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