Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/22/2015
Publication Date: 3/22/2015
Citation: Kelly, A.C., Kistler, H.C., Proctor, R., Ward, T.J. 2015. The origin, distribution, and evolution of Type A trichothecenes in the Fusarium graminearum species complex [abstract]. Fungal Genetics Conference.
Technical Abstract: Members of the Fusarium graminearum species complex (FGSC) are the major cause of Fusarium Head Blight (FHB) of cereal crops worldwide. FGSC strains typically produce one of three B trichothecenes (3ADON, 15ADON, NIV), which can contaminate grain and have toxic effects in animals and humans. Production of a novel Type A trichothecene (NX-2) by some strains of F. graminearum from the US was recently discovered. This unexpected trichothecene diversity is the result of polymorphisms in TRI1, a cytochrome P450 enzyme that contributes to structural differences in Type A and Type B trichothecenes. To understand the geographic and phylogenetic distribution of the NX-2 toxin type, we developed and used several DNA sequence-based approaches to screen 1,475 isolates from 22 different countries for the NX-2 allele at TRI1. Our data indicate that NX-2 production may currently be limited to F. graminearum isolates from Canada and the US (ND, SD, MN, CT), and that the distribution of NX-2 alleles mirrors that of the novel 3ADON population in North America. To investigate the evolutionary origins of NX-2, we assessed phylogeny and patterns of selective constraint at TRI1 using orthologous sequences from 40 Fusarium species. The TRI1 phylogeny was strikingly different from the species phylogeny, as F. graminearum isolates were not monophyletic. NX-2 F. graminearum were derived from a Type B ancestor, but they constituted a highly diverged clade. The ratio of nonsynonymous to synonymous substitution rates (') was significantly higher along the branch leading to the NX-2 clade in comparisons with the rest of the phylogeny ('NX-2 = 1.17, 'Type-B = 0.05). This finding is consistent with a substantial relaxation of evolutionary constraint at Tri1 during the evolution of the NX-2 lineage, possibly resulting from a partial loss of function or change in substrate recognition. Our results suggest that alterations to gene function have contributed to the evolution of metabolic diversity in the FGSC.