title: Medicago truncatula (E)-beta-ocimene synthase is induced by insect herbivory with corresponding increases in emission of volatile ocimene.
abstract: Virtually all plants are able to recognize attack by herbivorous insects and release volatile organic compounds (VOC) in response. Terpenes are the most abundant and varied class of insect-induced VOC from plants. Four genes encoding putative terpene synthases (MtTps1, MtTps2, MtTps3 and MtTps4) were shown to accumulate in Medicago truncatula Gaertn. in response to Spodoptera exigua (Hübner) feeding and methyl jasmonate treatment in a previous study [S.K. Gomez, M.M. Cox, J.C. Bede, K.K. Inoue, H.T. Alborn, J.H. Tumlinson, K.L. Korth, Lepidopteran herbivory and oral factors induce transcripts encoding novel terpene synthases in Medicago truncatula, Arch. Insect Biochem. Physiol. 58 (2005) 114-127.] The focus of the current study is the functional characterization of one (MtTps4) of these four genes. Using an M. truncatula cDNA clone, the insect-inducible putative terpene synthase was expressed in Escherichiacoli and shown to convert geranyl diphosphate (GPP) into the monoterpene (E)-beta-ocimene as the major product. The clone was therefore designated M. truncatula (E)-beta-ocimene synthase (MtEBOS). Transcripts encoding this enzyme accumulate in M. truncatula leaves in response to exogenous jasmonic acid treatments, lepidopteran herbivory, and lepidopteran oral secretions. Treatment with the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) did not cause an increase in MtEBOS transcripts. The volatile (E)-beta-ocimene was released from leaves of both undamaged and insect-damaged plants, but at levels two-fold higher in insect-damaged M. truncatula. Although leaves have low constitutive levels of MtEBOS transcripts, RNA blot analysis indicates no constitutive expression in flowers, stems or roots. The strong insect-induced expression of this gene, and its correspondence with release of volatile ocimene, suggest that it plays an active role in indirect insect defenses in M. truncatula.
authors.affiliation: Department of Plant Pathology, University of Arkansas, Fayetteville, 72701, USA.
authors.forename: Wayra G
authors.initials: WG
authors.lastname: Navia-Giné
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Yuan
authors.forename: Andy
authors.initials: A
authors.lastname: Mauromoustakos
authors.forename: J Brad
authors.initials: JB
authors.lastname: Murphy
authors.forename: Feng
authors.initials: F
authors.lastname: Chen
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Korth
mesh_terms: D000080462:Acyclic Monoterpenes; D000475:Alkenes / Q000378:metabolism*; D019883:Alkyl and Aryl Transferases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary / Q000235:genetics; D011756:Diphosphates / Q000378:metabolism; D004224:Diterpenes / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D008401:Gas Chromatography-Mass Spectrometry; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D006790:Host-Parasite Interactions; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007814:Larva / Q000502:physiology; D046913:Medicago truncatula / Q000235:genetics / Q000378:metabolism* / Q000469:parasitology; D008969:Molecular Sequence Data; D010802:Phylogeny; D010935:Plant Diseases / Q000469:parasitology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D018411:Spodoptera / Q000502:physiology; D013314:Stress, Mechanical; D055549:Volatile Organic Compounds / Q000378:metabolism
chemical_list: D000080462:Acyclic Monoterpenes; D000475:Alkenes; D018076:DNA, Complementary; D011756:Diphosphates; D004224:Diterpenes; D007527:Isoenzymes; D010940:Plant Proteins; D018749:RNA, Plant; D011994:Recombinant Proteins; D055549:Volatile Organic Compounds; C511282:geranyl diphosphate; C443996:beta-ocimene; D019883:Alkyl and Aryl Transferases; C108877:terpene synthase