two post-doctoral positions

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Mon Feb 12 20:04:28 EST 2001

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<font face=3D"Courier New, Courier">Two NSF-funded postdoctoral positions
are currently available for individuals interested in studying the
biochemical genetics of secondary metabolism in Arabidopsis. <br>
The first position will focus on the characterization of the ref8 mutant
of Arabidopsis and the enzyme encoded by the REF8 locus, the cytochrome
P450-dependent monooxygenase p-coumarate 3-hydroxylase.<br>
The end products of the phenylpropanoid pathway play important roles in
plant structure and plant growth and development, as well as in plants=92
defenses against biotic and abiotic stresses.&nbsp; From a human
perspective, phenylpropanoid pathway-derived metabolites influence both
human health and the potential utility of plants in agricultural
contexts.&nbsp; An important gap in our understanding of phenylpropanoid
metabolism is represented by p-coumarate 3-hydroxylase (C3H), the only
enzyme of the pathway that has not been characterized, and the enzyme
encoded by the only gene of the pathway that has not been cloned.&nbsp;
By screening for plants that fail to accumulate soluble fluorescent
phenylpropanoid secondary metabolites, we have identified a number of
Arabidopsis mutants that display a reduced epidermal fluorescence (ref)
phentoype. We have determined that the ref8 mutant is defective in the
gene encoding C3H.&nbsp; We have conducted a preliminary phenotypic
characterization of the ref8 mutant, have cloned the REF8 gene, and have
verified that it encodes C3H by expression of the wild-type gene in
yeast.&nbsp; Our goals are to characterize this poorly-studied enzyme, to
clarify its role in the phenylpropanoid pathway, to identify when and
where the protein is expressed, and to determine why ref8 mutations lead
to alterations in plant growth and development.<br>
=20 From an applied perspective, C3H functions at a branch point in the
phenylpropanoid pathway and may thereby regulate the relative fluxes of
phenylpropanoid units toward flavonoids versus hydroxycinnamic acid and
lignin biosynthesis.&nbsp; Downregulating REF8 activity could redirect
carbon toward the synthesis of isoflavonoids that could improve plant
disease resistance or add nutraceutical value to foods.&nbsp;
Alternatively, the same strategy could decrease lignin biosynthesis in
forest species used in pulp production, or in herbaceous species used as
forages or for the production of bio-fuels.&nbsp; The isolation of the
REF8 gene will permit us to determine whether these strategies will be
useful in the modification of phenylpropanoid metabolism in
agriculturally important plants. <br>
The second position will focus on the functional analysis of the serine
carboxypeptidase-like (SCPL) gene family of Arabidopsis. <br>
Although their name suggests that they are involved in protein turnover
or processing, the role of SCPL proteins in plant metabolism is
enigmatic.&nbsp; We have identified two new Arabidopsis mutants, sng1 and
sng2, (sinapoylglucose accumulator 1 and 2) that are defective in the
synthesis of sinapic acid esters, one of the major classes of
phenylpropanoid secondary metabolites in the Brassicaceae.&nbsp; We have
cloned the gene that is defective in sng1 and have found that it encodes
the SCPL protein, sinapoylglucose:malate sinapoyltransferase (SMT).&nbsp;
(Lehfeldt et al. (2000) Cloning of the SNG1 gene of Arabidopsis reveals a
role for a serine carboxypeptidase-like protein as an acyltransferase in
secondary metabolism.&nbsp; Plant Cell 12: 1295-1306). The SNG1 gene is
flanked by five other SCPL genes, and we have recently identified mutant
phenotypes associated with sinapic acid metabolism caused by defects in
some of these genes.&nbsp; Finally, we are currently completing the
map-based cloning of the SNG2 gene, and have shown that it encodes
another SCPL protein.<br>
The specific aims of this project are to characterize the SMT protein
with particular emphasis on its enzymatic mechanism, to characterize
Arabidopsis mutants that are defective in SCPL genes that flank the SNG1
gene, and to elucidate the pathways in which the encoded proteins
participate, to characterize the enzymes encoded by the SCPL genes
flanking SNG1, and to clone the SNG2 gene and characterize the SNG2
protein. Through this approach, we expect to elucidate the function of
several SCPL proteins in plants, and begin to understand how enzymes of
this type are capable of catalyzing transacylation reactions.<br>
=46or more information see
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Qualifications:&nbsp; A Ph.D. in molecular biology or biochemistry.&nbsp;
Experience with biochemical techniques such heterologous protein
expression and protein purification, gas chromatography / mass
spectrometry, or HPLC is desirable.&nbsp; Interested individuals should
submit a CV and the names of three references (including email
addresses), preferably by e-mail to:<br>
Dr. Clint Chapple, Department of Biochemistry, Purdue University, West
Lafayette IN 47907-1153; fax 765-496-7213, e-mail
chapple at<br>
Purdue University is an Equal Opportunity / Affirmative Action
<div>Clint Chapple</div>
<div>Department of Biochemistry</div>
<div>Purdue University</div>
<div>West Lafayette, IN 47907-1153</div>
<div>TEL:&nbsp; 765-494-0494</div>
<div>FAX:&nbsp; 765-496-7213</div>



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