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postdoc positions

Tai-ping Sun tps at acpub.duke.edu
Fri May 30 15:26:02 EST 2003

Postdoctoral Positions in the Dept. of Biology, Duke University:
Two postdoctoral positions (funded by NSF & USDA) are available 
immediately to study "Gibberellin Signaling Pathway in Arabidopsis" &
"Developmental Regulation of Gibberellin Biosynthesis in Arabidopsis"

Gibberellin Signaling Pathway in Arabidopsis:

Bioactive gibberellins (GAs) are plant growth regulators, which 
control such diverse processes as germination, stem elongation, and 
flower and fruit development.  The RGA gene encodes a negative 
regulator of GA response in Arabidopsis.   Several structural 
features in the RGA protein suggest that it may be a transcriptional 
regulator.  In support of this, we showed that a green fluorescent 
protein (GFP)-RGA fusion protein is localized to the nucleus in 
transgenic Arabidopsis plants.  Confocal microscopy and immunoblot 
analyses demonstrated that GA activates its signaling pathway by 
causing the degradation of the RGA protein, and the DELLA motif near 
the N terminus of RGA is required for GA-induced degradation of this 
protein.  The ubiquitin-proteasome pathway is likely to play a role 
in RGA degradation. SLEEPY1 (SLY1), an activator of GA signaling, is 
an F-box protein.  RGA protein accumulates to a high level in the 
sly1 mutant, suggesting that RGA is a target of the SCFSLY1 complex 
(an ubiquitin E3 ligase).    Using biochemical and genetic 
approaches, we are currently investigating the mechanism by which GA 
regulates the stability of RGA.  We are also using microarray 
analysis to identify the downstream targets of RGA.

Related publications:

Silverstone et al. (2001) Repressing a repressor: gibberellin-induced 
rapid reduction of the RGA protein in Arabidopsis.  Plant Cell 13, 

Dill and Sun (2001) Synergistic derepression of gibberellin signaling 
by removing RGA and GAI function in Arabidopsis thaliana.  Genetics 
159, 777-785.

Dill et al. (2001) The DELLA motif is essential for 
gibberellin-induced degradation of RGA.  Proc. Natl. Acad. Sci. USA. 
98, 14162-14167.

Olszewski et al. (2002) Gibberellin signaling: Biosynthesis, 
catabolism and response pathways.  Plant Cell Supplement, S61-S80.

McGinnis et al. (2003) The Arabidopsis SLEEPY1 (SLY1) gene encodes a 
putative F-box subunit of an SCF E3 ubiquitin ligase. Plant Cell. 15, 

Developmental Regulation of Gibberellin (GA) Biosynthesis in Arabidopsis:

The final biosynthetic step to produce bioactive GAs is catalyzed by 
GA 3-oxidase, which is encoded by four homologous genes in 
Arabidopsis (AtGA3ox1 to 3ox4).  We are investigating the relative 
physiological function of these genes in regulating the synthesis of 
bioactive GAs at different development stages of the plant. 
Expression patterns of these genes are being examined by in situ 
hybridization and by analysis of transgenic plants expressing the 
promoter-reporter gene fusions.  To determine the roles of the  4 
AtGA3ox genes in modulating the levels of bioactive GAs during plant 
growth, we have isolated mutants with T-DNA insertions in these loci. 
Initial results indicated that each gene has an unique 
tissue-specific expression pattern.  Phenotypic characterization of 
single and multiple GA3ox mutants in combination with the expression 
studies will help to reveal the sites of GA biosynthesis and the 
potential role of GA transport in plant development.

Related publications:

Yamaguchi et al. (1998) Phytochrome regulation and differential 
expression of gibberellin 3b-hydroxylase genes in germinating 
Arabidopsis seeds.  Plant Cell 10, 2115-2126.

Yamaguchi et al. (2001) Distinct cell-specific expression patterns of 
early and late gibberellin biosynthetic genes during Arabidopsis seed 
germination.  Plant J. 28, 443-453.

Olszewski et al. (2002) Gibberellin signaling: Biosynthesis, 
catabolism and response pathways.  Plant Cell Supplement, S61-S80.

A background in protein chemistry, genetics, molecular biology or 
plant development is desirable.  If you are interested in applying, 
please send (by e-mail) a curriculum vitae and names, e-mail 
addresses, and phone numbers of three references to:

Tai-ping Sun
e-mail address: tps at duke.edu

Tai-ping Sun
Associate Professor
Department of Biology
LSRC B327, Box 91000
Duke University
Durham, NC 27708-1000

e-mail: tps at acpub.duke.edu
TEL: (919)-613-8166
FAX: (919)-613-8177

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