The geographic distribution and complex evolutionary history of the NX-2 trichothecene chemotype from Fusarium graminearum

• Autores: Kelly, Amy; Proctor, Robert H.; Belzile, Francois; Chulze, Sofia Noemi; Clear, Randall M.; Cowger, Christina; Elmer, Wade; Lee, Theresa; Obanor, Friday; Waalwijk, Cees; Ward, Todd J.
• Año de publicación: 2016
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Fusarium Head Blight; Molecular Evolution; Nx-2; Phylogenetics; Tri1; Trichothecene
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

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.
Fil: Kelly, Amy. United States Department of Agriculture; Estados Unidos
Fil: Proctor, Robert H.. United States Department of Agriculture; Estados Unidos
Fil: Belzile, Francois. Laval University; Canadá
Fil: Chulze, Sofia Noemi. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Microbiología e Inmunología. Cátedra de Micología; Argentina. United States Department of Agriculture; Estados Unidos
Fil: Clear, Randall M.. Winnipeg; Canadá
Fil: Cowger, Christina. University of North Carolina; Estados Unidos
Fil: Elmer, Wade. The Connecticut Agricultural Experiment Station; Estados Unidos
Fil: Lee, Theresa. National Institute of Agricultural Sciences; Corea del Sur
Fil: Obanor, Friday. Commonwealth Scientific and Industrial Research Organization; Australia
Fil: Waalwijk, Cees. University of Agriculture Wageningen; Países Bajos
Fil: Ward, Todd J.. United States Department of Agriculture; Estados Unidos