Biochemical, Molecular and Functional Analysis of Volatile Terpene Formation in Arabidopsis Roots

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dc.contributor.authorHuh, Jung-Hyunen
dc.contributor.committeechairTholl, Dorotheaen
dc.contributor.committeememberSchmale, David G. IIIen
dc.contributor.committeememberWinkel, Brenda S. J.en
dc.contributor.committeememberVinatzer, Boris A.en
dc.contributor.committeememberTokuhisa, James G.en
dc.contributor.departmentBiologyen
dc.date.accessioned2017-04-06T15:43:11Zen
dc.date.adate2011-08-25en
dc.date.available2017-04-06T15:43:11Zen
dc.date.issued2011-07-20en
dc.date.rdate2016-09-30en
dc.date.sdate2011-08-02en
dc.description.abstractPlants produce secondary (or specialized) metabolites to respond to a variety of environmental changes and threats. Especially, volatile compounds released by plants facilitate short and long distance interaction with both beneficial and harmful organisms. Comparatively little is known about the organization and role of specialized metabolism in root tissues. In this study, we have investigated the root-specific formation and function of volatile terpenes in the model plant Arabidopsis. As one objective, we have characterized the two root-specific terpene synthases, TPS22 and TPS25. Both enzymes catalyze the formation of several volatile sesquiterpenes with (E)-β-farnesene as the major product. TPS22 and TPS25 are expressed in the root in distinct different cell type-specific patterns and both genes are induced by jasmonic acid. Unexpectedly, both TPS proteins are localized to mitochondria, demonstrating a subcellular localization of terpene specialized metabolism in compartments other than the cytosol and plastids. (E)-β-Farnesene is produced at low concentrations suggesting posttranslational modifications of the TPS proteins and/or limited substrate availability in mitochondria. We hypothesize that the mitochondrial localization of TPS22 and TPS25 reflects evolutionary plasticity in subcellular compartmentation of TPS proteins with emerging or declining activity. Since (E)-β-farnesene inhibits Arabidopsis root growth in vitro, mitochondrial targeting of both proteins may fine tune (E)-β-farnesene concentrations to prevent possible autotoxic or inhibitory effects of this terpene in vivo. We further investigated the role of volatile terpenes in Arabidopsis roots in interaction with the soil-borne oomycete, Pythium irregulare. Infection of roots with P. irregulare causes emission of the C11-homoterpene (or better called C4-norterpene) 4,8-dimethylnona-1,3,7-triene (DMNT), which is a common volatile induced by biotic stress in aerial parts of plants but was not previously known to be produced in plant roots. We demonstrate that DMNT is synthesized by a novel, root-specific pathway via oxidative degradation of the C30-triterpene, arabidiol. DMNT exhibits inhibitory effects on P. irregulare mycelium growth and oospore germination in vitro. Moreover, arabidiol and DMNT biosynthetic mutants were found to be more susceptible to P. irregulare infection and showed higher rates of Pythium colonization in comparison to wild type plants. Together, our studies demonstrate differences and plasticity in the metabolic organization and function of terpenes in roots in comparison to aboveground plant tissues.en
dc.description.degreePh. D.en
dc.identifier.otheretd-08022011-201456en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-08022011-201456/en
dc.identifier.urihttp://hdl.handle.net/10919/77151en
dc.language.isoen_USen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectsecondary (specialized) metabolismen
dc.subjectplant volatilesen
dc.subjectterpene synthaseen
dc.subjectsoil-borne pathogenen
dc.subjectoomyceteen
dc.subjectPythiumen
dc.subjectsesquiterpeneen
dc.subjectroot chemical defenseen
dc.titleBiochemical, Molecular and Functional Analysis of Volatile Terpene Formation in Arabidopsis Rootsen
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplineBiologyen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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