Caterpillar herbivory and salivary enzymes decrease transcript levels of Medicago truncatula genes encoding early enzymes in terpenoid biosynthesis

  • Bede J
  • Musser R
  • Felton G
 et al. 
  • 101


    Mendeley users who have this article in their library.
  • 102


    Citations of this article.


In response to caterpillar herbivory, alfalfa and related plant species defend themselves through the induction of saponin and volatile terpenoid biosynthesis. Both these types of defensive compounds are derived from the metabolic intermediate, isopentenyl diphosphate (IPP). In plants, two distinct biosynthetic pathways can generate IPP; the cytosolic mevalonate pathway and the plastid-associated 2C-methyl erythritol 4-phosphate (MEP) pathway. In Medicago truncatula, transcript levels of key regulatory genes active in the early steps of these biosynthetic pathways were measured in response to larval herbivory by the beet army worm, Spodoptera exigua. Transcripts encoding enzymes at early steps of both terpenoid pathways were lower in caterpillar-damaged leaves. Higher degrees of herbivore damage accentuated the decrease in transcript levels; however, transcript amounts were not affected by insect larval stage. Insect larvae, manipulated to reduce labial gland salivary secretions, were used to examine the role of the salivary elicitors in modulating gene expression. Results suggest that an insect salivary factor, possibly glucose oxidase (GOX), may be involved in reduction of transcript levels following herbivory. Addition of GOX or hydrogen peroxide to mechanically wounded leaves confirm these findings. In comparison, transcript levels of a gene encoding a putative terpene synthase are induced in mechanically- or insect-damaged leaves. These data show that insect salivary factors can act to suppress transcript levels of genes involved in plant defense pathways. Findings also suggest that in response to stress such as insect herbivory, regulation occurs at the early steps of the MEP pathway.

Author-supplied keywords

  • 2C-methyl erythritol 4-phosphate (MEP) pathway
  • Glucose oxidase
  • Indole
  • Mevalonate (MVA) pathway

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document


  • Gary FeltonPennsylvania State University

  • Jacqueline C. Bede

  • Richard O. Musser

  • Kenneth L. Korth

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free