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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Saponin Biosynthesis in Saponaria vaccaria. cDNAs Encoding -Amyrin Synthase and a Triterpene Carboxylic Acid Glucosyltransferase^1,[OA]

Plant Biotechnology Institute, Saskatoon, Saskatchewan, Canada S7N OW9

Saponaria vaccaria (Caryophyllaceae), a soapwort, known in western Canada as cowcockle, contains bioactive oleanane-type saponins similar to those found in soapbark tree (Quillaja saponaria; Rosaceae). To improve our understanding of the biosynthesis of these saponins, a combined polymerase chain reaction and expressed sequence tag approach was taken to identify the genes involved. A cDNA encoding a -amyrin synthase (SvBS) was isolated by reverse transcription-polymerase chain reaction and characterized by expression in yeast (Saccharomyces cerevisiae). The SvBS gene is predominantly expressed in leaves. A S. vaccaria developing seed expressed sequence tag collection was developed and used for the isolation of a full-length cDNA bearing sequence similarity to ester-forming glycosyltransferases. The gene product of the cDNA, classified as UGT74M1, was expressed in Escherichia coli, purified, and identified as a triterpene carboxylic acid glucosyltransferase. UGT74M1 is expressed in roots and leaves and appears to be involved in monodesmoside biosynthesis in S. vaccaria.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Patrick S. Covello (patrick.covello{at}nrc-cnrc.gc.ca).

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www.plantphysiol.org/cgi/doi/10.1104/pp.106.088484

^* Corresponding author; e-mail patrick.covello{at}nrc-cnrc.gc.ca; fax 306–975–4839.

Received August 18, 2006; accepted November 27, 2006; published December 15, 2006.