HMG-GoA reductase and terpenoid phytoalexins: Molecular specialization within a complex pathway |
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Authors: | Deborah L. Weissenborn,Cynthia J. Denbow,Marko Laine,Saara S. Lå ng,Zhenbiao Yang,Xueshu Yu,Carole L. Cramer |
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Affiliation: | Dept of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061–0330, USA. |
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Abstract: | Terpenoid phytoalexins and other defense compounds play an important role in disease resistance in a variety of plant families but have been most widely studied in solanaceous species. The rate-limiting step in terpenoid phytoalexin production is mediated by 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), which catalyzes mevalonic acid synthesis. HMGRs are involved in the biosynthesis of a broad array of terpenoid compounds, and distinct isoforms of HMGR may be critical in directing the flux of pathway intermediates into specific end products. Plant HMGRs are encoded by a small gene family, and genomic or cDNA sequences encoding HMGR have been isolated from several plant species. In tomato, four genes encode HMGR; these genes are differentially activated during development and stress responses. One gene, hmg 2 , is activated in response to wounding and a variety of pathogenic agents suggesting a role in sesquiterpene phytoalexin biosynthesis. In contrast, expression patterns of tomato hmg l suggest a role in sterol biosynthesis and cell growth. Other plant species show an analogous separation of specific HMGR isoforms involved in growth and/or housekeeping function and inducible isoforms associated with biosynthesis of phytoalexins or other specialized "natural products". We are applying a variety of cell and molecular techniques to address whether subcellular localization and/or differential expression of these isoforms are key factors in determining end product accumulation during development and defense. |
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Keywords: | Differential isogene expression hydroxymethylglutaryl CoA reductase pathway partitioning sesquiterpene phytoalexins |
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