Location: Chemistry Research Unit
Title: An amino acid substitution inhibits specialist herbivore production of a competitive antagonist effector and recovers insect-induced plant defenses Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2013
Publication Date: N/A
Technical Abstract: Plants respond to insect herbivory through the production of biochemicals that function as either direct defenses or indirect defenses via the attraction of natural enemies. Curiously, attack by even closely related insect pests can result in distinctive levels of induced plant defenses. Despite these observations, precise biochemical mechanisms responsible for differing plant responses remain largely unknown. Cowpea (Vigna unguiculata) plants respond to Fall armyworm (FAW; Spodoptera frugiperda) herbivory through the detection of fragments of ATP synthase '-subunit (cATPC) proteins, termed inceptin-related peptides, present in larval oral secretions (OS). In contrast to generalists like FAW, OS of the legume specializing Velvetbean caterpillar (VBC; Anticarsia gemmatalis) does not elicit ethylene production and demonstrates significantly lower induced volatile emission in direct herbivory comparisons. Unlike all other Lepidoptera examined which preferentially harbor the inceptin [Vu-In; +ICDINGVCVDA-] elicitor, VBC OS contains predominantly a C-terminal truncated peptide Vu-In-A [+ICDINGVCVD-]. Vu-In-A is both inactive and functions as potent naturally occurring competitive antagonist of Vu-In induced responses. Amino acid substitutions at the Vu-In C-terminus were screened for differences in VBC gut proteolysis and revealed a valine substituted peptide [Vu-In'V; +ICDINGVCVDV-] that retained full activity. Compared to the native polypeptide, VBC that previously ingested 500 pmols of a modified cATPC precursor elicited significantly stronger plant responses in herbivory assays. We demonstrate that a specialist herbivore minimizes the activation of defenses by converting an elicitor into a competitive antagonist effector and identify an amino acid substitution that recovers these induced plant defenses to a level observed with generalist herbivores.