title: Novel acidic sesquiterpenoids constitute a dominant class of pathogen-induced phytoalexins in maize.
abstract: Nonvolatile terpenoid phytoalexins occur throughout the plant kingdom, but until recently were not known constituents of chemical defense in maize (Zea mays). We describe a novel family of ubiquitous maize sesquiterpenoid phytoalexins, termed zealexins, which were discovered through characterization of Fusarium graminearum-induced responses. Zealexins accumulate to levels greater than 800 μg g⁻¹ fresh weight in F. graminearum-infected tissue. Their production is also elicited by a wide variety of fungi, Ostrinia nubilalis herbivory, and the synergistic action of jasmonic acid and ethylene. Zealexins exhibit antifungal activity against numerous phytopathogenic fungi at physiologically relevant concentrations. Structural elucidation of four members of this complex family revealed that all are acidic sesquiterpenoids containing a hydrocarbon skeleton that resembles β-macrocarpene. Induced zealexin accumulation is preceded by increased expression of the genes encoding TERPENE SYNTHASE6 (TPS6) and TPS11, which catalyze β-macrocarpene production. Furthermore, zealexin accumulation displays direct positive relationships with the transcript levels of both genes. Microarray analysis of F. graminearum-infected tissue revealed that Tps6/Tps11 were among the most highly up-regulated genes, as was An2, an ent-copalyl diphosphate synthase associated with production of kauralexins. Transcript profiling suggests that zealexins cooccur with a number of antimicrobial proteins, including chitinases and pathogenesis-related proteins. In addition to zealexins, kauralexins and the benzoxazinoid 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one-glucose (HDMBOA-glucose) were produced in fungal-infected tissue. HDMBOA-glucose accumulation occurred in both wild-type and benzoxazine-deficient1 (bx1) mutant lines, indicating that Bx1 gene activity is not required for HDMBOA biosynthesis. Together these results indicate an important cooperative role of terpenoid phytoalexins in maize biochemical defense.
authors.affiliation: Center for Medical, Agricultural, and Veterinary Entomology, United States Department of Agriculture, Agricultural Research Service, Chemistry Research Unit, Gainesville, Florida 32608, USA. alisa.huffaker@ars.usda.gov
authors.forename: Alisa
authors.initials: A
authors.lastname: Huffaker
authors.forename: Fatma
authors.initials: F
authors.lastname: Kaplan
authors.forename: Martha M
authors.initials: MM
authors.lastname: Vaughan
authors.forename: Nicole J
authors.initials: NJ
authors.lastname: Dafoe
authors.forename: Xinzhi
authors.initials: X
authors.lastname: Ni
authors.forename: James R
authors.initials: JR
authors.lastname: Rocca
authors.forename: Hans T
authors.initials: HT
authors.lastname: Alborn
authors.forename: Peter E A
authors.initials: PE
authors.lastname: Teal
authors.forename: Eric A
authors.initials: EA
authors.lastname: Schmelz
mesh_terms: D000143:Acids / Q000378:metabolism*; D000818:Animals; D003517:Cyclopentanes / Q000378:metabolism; D005030:Ethylenes / Q000378:metabolism; D005247:Feeding Behavior / Q000187:drug effects; D005658:Fungi / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D008401:Gas Chromatography-Mass Spectrometry; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D007313:Insecta / Q000187:drug effects; D054883:Oxylipins / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012717:Sesquiterpenes / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D003313:Zea mays / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology*; D000094162:Phytoalexins
chemical_list: D000143:Acids; D003517:Cyclopentanes; D005030:Ethylenes; D054883:Oxylipins; D010940:Plant Proteins; D012333:RNA, Messenger; D012717:Sesquiterpenes; C011006:jasmonic acid; C036216:ethylene; D000094162:Phytoalexins