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First published online March 16, 2007; 10.1104/pp.107.097154 Plant Physiology 144:793-805 (2007) © 2007 American Society of Plant Biologists OPEN ACCESS ARTICLE
Cowpea Chloroplastic ATP Synthase Is the Source of Multiple Plant Defense Elicitors during Insect Herbivory1,2,[W],[OA]Center of Medical, Agricultural, and Veterinary Entomology, United States Department of Agriculture, Agricultural Research Service, Chemistry Research Unit, Gainesville, Florida 32608
In cowpea (Vigna unguiculata), fall armyworm (Spodoptera frugiperda) herbivory and oral secretions (OS) elicit phytohormone production and volatile emission due to inceptin [Vu-In; +ICDINGVCVDA–], a peptide derived from chloroplastic ATP synthase
1 This work was supported by the U.S. Department of Agriculture, Agricultural Research Service (base funds directed to project no. 6615–22430–002–00D). 2 The use of trade, firm, or corporation names in this publication (or page) is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the United States Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Eric A. Schmelz (eschmelz{at}gainesville.usda.ufl.edu). [W] The online version of this article contains Web-only data. [OA] Open Access articles can be viewed online without a subscription. www.plantphysiol.org/cgi/doi/10.1104/pp.107.097154 * Corresponding author; e-mail eschmelz{at}gainesville.usda.ufl.edu; fax 352–374–5707. Received January 31, 2007; accepted March 5, 2007; published March 16, 2007. This article has been cited by other articles:
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-subunit (cATPC) proteins. Elicitor-induced plant volatiles can function as attractants for natural enemies of insect herbivores. We hypothesized that inceptins are gut proteolysis products and that larval OS should contain a mixture of related peptides. In this study, we identified three additional cATPC fragments, namely Vu-GE+In [+GEICDINGVCVDA–], Vu-E+In [+EICDINGVCVDA–], and Vu-In–A [+ICDINGVCVD–]. Leaf bioassays for induced ethylene (E) production demonstrated similar effective concentration50 values of 68, 45, and 87 fmol leaf–1 for Vu-In, Vu-E+In, and Vu-GE+In, respectively; however, Vu-In–A proved inactive. Shortly following ingestion of recombinant proteins harboring cATPC sequences, larval OS revealed similar concentrations of the three elicitors with 80% of the potential inceptin-related peptides recovered. Rapidly shifting peptide ratios over time were consistent with continued proteolysis and preferential stability of inceptin. Likewise, larvae ingesting host plants with inceptin precursors containing an internal trypsin cleavage site rapidly lost OS-based elicitor activity. OS containing inceptin elicited a rapid and sequential induction of defense-related phytohormones jasmonic acid, E, and salicylic acid at 30, 120, and 240 min, respectively, and also the volatile (E)-4,8-dimethyl-1,3,7-nonatriene. Similar to established peptide signals such as systemin and flg22, amino acid substitutions of Vu-In demonstrate an essential role for aspartic acid residues and an unaltered C terminus. In cowpea, insect gut proteolysis following herbivory generates inappropriate fragments of an essential metabolic enzyme enabling plant non-self-recognition. 
