University of Arkansas, Fayetteville
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Abstract

In addition to having numerous applications and pharmaceuticals, terpenoids are an important class of defensive compounds that can accumulate in plants after pathogen infection or injury by insects. Sequences of DNA encoding putative terpene synthases and an oxidosqualene synthase, isolated from insect-damaged Medicago truncatula leaves, were selected from an expressed sequence tag (EST) data base. The cDNA clones were used as radio-labeled probes to analyze gene expression in leaves treated with factors known to trigger a defense response in plants. Transcript levels for all of the genes examined increased in response to artificial wounding, insect herbivory, and methyl jasmonate (meJA) treatments, whereas salicylic acid (SA) and glucose oxidase (GOA) had no measurable effects on transcript levels. Furthermore, the genome of M. truncatula was analyzed via DNA blots for an estimation of the -number of copies of enzyme isoforms and indicate that each of the enzymes examined is encoded by a single-copy gene or a small gene family. The results show that M. truncatula can serve as a valuable source for novel terpene synthase clones and potentially for strong wound-inducible regulatory elements.

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