University of Arkansas, Fayetteville Division of Agriculture
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Abstract

Terpenoids are an important class of defensive compounds that can accumulate in plants after pathogen infection or injury by chewing insects. Clones encoding putative terpene synthases and an oxidosqualene synthase, isolated from insect-damaged Medicagotruncatula leaves, were selected from an expressed sequence tag (EST) database. The cDNA clones were used as radiolabeled probes to analyze gene expression in leaves treated by known factors that can 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 (GOX) 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; these data indicate that each of the enzymes examined is encoded by a single-copy gene or a small gene family.

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