title: The geographic distribution and complex evolutionary history of the NX-2 trichothecene chemotype from Fusarium graminearum.
abstract: Fusarium graminearum and 21 related species comprising the F. sambucinum species complex lineage 1 (FSAMSC-1) are the most important Fusarium Head Blight pathogens of cereal crops world-wide. FSAMSC-1 species typically produce type B trichothecenes. However, some F. graminearum strains were recently found to produce a novel type A trichothecene (NX-2) resulting from functional variation in the trichothecene biosynthetic enzyme Tri1. We used a PCR-RFLP assay targeting the TRI1 gene to identify the NX-2 allele among a global collection of 2515 F. graminearum. NX-2 isolates were only found in southern Canada and the northern U.S., where they were observed at low frequency (1.8%), but over a broader geographic range and set of cereal hosts than previously recognized. Phylogenetic analyses of TRI1 and adjacent genes produced gene trees that were incongruent with the history of species divergence within FSAMSC-1, indicating trans-species evolution of ancestral polymorphism. In addition, placement of NX-2 strains in the TRI1 gene tree was influenced by the accumulation of nonsynonymous substitutions associated with the evolution of the NX-2 chemotype, and a significant (P<0.001) change in selection pressure was observed along the NX-2 branch (ω=1.16) in comparison to other branches (ω=0.17) in the TRI1 phylogeny. Parameter estimates were consistent with positive selection for specific amino-acid changes during the evolution of NX-2, but direct tests of positive selection were not significant. Phylogenetic analyses of fourfold degenerate sites and intron sequences in TRI1 indicated the NX-2 chemotype had a single evolutionary origin and evolved recently from a type B ancestor. Our results indicate the NX-2 chemotype may be indigenous, and possibly endemic, to southern Canada and the northern U.S. In addition, we demonstrate that the evolution of TRI1 within FSAMSC-1 has been complex, with evidence of trans-species evolution and chemotype-specific shifts in selective constraint.
authors: U.S. Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL 61604, USA.
authors: Amy
authors: A
authors: Kelly
authors: U.S. Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL 61604, USA.
authors: Robert H
authors: RH
authors: Proctor
authors: Université Laval, 1030 avenue de la Médecine, Québec City, Québec G1V 0A6, Canada.
authors: Francois
authors: F
authors: Belzile
authors: Universidad Nacional de Río Cuarto-CONICET, Rutas 8 and 36 Km 601, 5800 Rio Cuarto, Córdoba, Argentina.
authors: Sofia N
authors: SN
authors: Chulze
authors: 23 Healy Crescent, Winnipeg, Manitoba R2N 2S6, Canada.
authors: Randall M
authors: RM
authors: Clear
authors: U.S. Department of Agriculture, Agricultural Research Service, 3411 Gardner Hall, North Carolina State University, Raleigh, NC 27695, USA.
authors: Christina
authors: C
authors: Cowger
authors: The Connecticut Agricultural Experiment Station, 123 Huntington St, New Haven, CT 06504, USA.
authors: Wade
authors: W
authors: Elmer
authors: National Institute of Agricultural Sciences, 166 Nongsaengmyeong-ro, Iseo-myeon, Wanju-gun, Jeollabuk-do 55365, Republic of Korea.
authors: Theresa
authors: T
authors: Lee
authors: Commonwealth Scientific and Industrial Research Organization, 306 Carmody Road, St Lucia, QLD 4067, Australia.
authors: Friday
authors: F
authors: Obanor
authors: Plant Research International, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors: Cees
authors: C
authors: Waalwijk
authors: U.S. Department of Agriculture, Agricultural Research Service, 1815 North University Street, Peoria, IL 61604, USA. Electronic address: todd.ward@ars.usda.gov.
authors: Todd J
authors: TJ
authors: Ward
mesh_terms: D000595:Amino Acid Sequence; D044822:Biodiversity; D002170:Canada; D004271:DNA, Fungal / Q000032:analysis / Q000235:genetics; D002523:Edible Grain / Q000382:microbiology; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics; D005670:Fusarium / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D005800:Genes, Fungal / Q000235:genetics*; D005843:Geography; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D012150:Polymorphism, Restriction Fragment Length; D013045:Species Specificity; D014255:Trichothecenes / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D014481:United States
chemical_list: D004271:DNA, Fungal; D005656:Fungal Proteins; D014255:Trichothecenes
keywords: Fusarium head blight; Molecular evolution; NX-2; Phylogenetics; TRI1; Trichothecene