中文摘要：禾谷镰刀菌和21种包括FSAMSC-1在内的相关镰刀菌是世界上谷类作物最重要的镰刀菌枯萎病病原菌。FSAMSC-1菌种通常产生B型单端孢霉烯。然而最近发现，一些禾谷镰刀菌柱由于单端孢霉烯生物合成酶 Tri1的功能性变异产生了一种新的A型单端孢霉烯（NX-2）。作者从2515例从全球收集得到的禾谷镰刀菌样品中，以TRI1为靶向基因通过PCR-RFLP方法来鉴定NX-2等位基因。研究发现，仅仅在加拿大南部和美国北部发现了NX-2分离株，NX-2可能是这些地方的原生物种，而且可能是地方性流行病毒。另外，FSAMSC-1内TRI1的进化复杂，为跨物种进化和化学特异性转移等研究提供了证据。
外文摘要：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.
外文关键词：Fusarium head blight;Trichothecene;NX-2;TRI1;Phylogenetics;Molecular
作者：Kelly, Amy; Proctor, Robert H.; Belzile, Francois; Chulze, Sofia N.;Clear, Randall M.; Cowger, Christina; Elmer, Wade; Lee, Theresa; Obanor,Friday; Waalwijk, Cees; Ward, Todd J.
作者单位：USDA，USA
期刊名称：FUNGAL GENETICS AND BIOLOGY
期刊影响因子：2.933
出版年份：2016
出版刊次：10
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