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Characterization of the Monoterpene Synthase Gene tps26, the Ortholog of a Gene Induced by Insect Herbivory in Maize^1,[W],[OA]

Waksman Institute, Rutgers University, Piscataway, New Jersey 08855 (C.L., B.S., Z.X., H.K.D.); Department of Plant Biology, Rutgers University, New Brunswick, New Jersey 08901 (B.S., Z.X., H.K.D.); and Max Planck Institute for Chemical Ecology, D–07745 Jena, Germany (T.G.K., J.D.)

Plants damaged by insects can synthesize and release volatile chemicals that attract natural enemies of the herbivore. The maize (Zea mays subsp. mays) terpene synthase gene stc1 is part of that indirect defense response, being induced in seedling blades in response to herbivory by beet army worm. Many genes in maize are duplicated because of a past whole-genome duplication event, and several of these orthologs display different expression patterns. We report here the isolation and characterization of tps26 and confirm by homology and synteny criteria that it is the ortholog of stc1. Prior genetic analysis revealed that the stc1 function is not duplicated, raising the interesting question of how the two orthologs have become differentiated in their expression. tps26 encodes a 633-amino acid protein that is highly conserved with STC1. Like stc1, tps26 is induced by wounding, but in the roots and leaf sheath, instead of the blade, and not in response to beet army worm feeding. tps26 maps near a quantitative trait locus for Southwestern corn borer resistance, making it a plausible candidate gene for that quantitative trait locus. However, while possessing highly polymorphic tps26 alleles, the resistant and susceptible parents of the mapping population do not differ in levels of tps26 expression. Moreover, tps26 is not induced specifically by Southwestern corn borer feeding. Therefore, although they share a wounding response, the stc1 and tps26 maize orthologs differ in their tissue specificity and their induction by insect herbivores. The N termini of STC1 and TPS26 are predicted to encode plastid transit peptides; fusion proteins of green fluorescent protein to either N terminus localized to the plastid, confirming that prediction. The mature proteins, but not the respective complete proteins, were active and synthesized a blend of monoterpenes, indicating that they are monoterpene synthases. A gene closely related to stc1/tps26 is found in the sorghum (Sorghum spp.) genome at a location that is not orthologous with stc1. The possible origin of stc1-like genes is discussed.

² Present address: Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114.

³ Present address: Department of Pathology and Laboratory Medicine, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854.

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: Hugo K. Dooner (dooner{at}waksman.rutgers.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.107.109553

^* Corresponding author; e-mail dooner{at}waksman.rutgers.edu.

Received September 22, 2007; accepted January 14, 2008; published January 24, 2008.