Convergent Evolution of C239S Mutation in Pythium spp. β-Tubulin Coincides with Inherent Insensitivity to Ethaboxam and Implications for Other Peronosporalean Oomycetes

• DOI: 10.1094/phyto-01-19-0022-r
• Publication Date: 2019-05-09T20:11:21Z
• Authors: Zachary A. Noel; Hyunkyu Sang; Mitchell G. Roth; Martin I. Chilvers
• Keywords: Oomycete; Transversion; Pythium; Pythium aphanidermatum; Monophyly; Lineage (genetic)

Ethaboxam is a benzamide antioomycete chemical (oomicide) used in corn and soybean seed treatments. Benzamides are hypothesized to bind β-tubulin, thus disrupting microtubule assembly. Recently, there have been reports of corn- soybean-associated oomycetes that insensitive ethaboxam despite never having exposed. Here, we investigate the evolutionary history molecular mechanism insensitivity. We tested sensitivity 194 isolates representing 83 species across four oomycete genera Peronosporalean lineage were exposed ethaboxam. In all, 84% sensitive (effective concentration reduce optical density at 600 nm by 50% when compared with nonamended control [EC50] < 5 μg ml-1), whereas 16% (EC50 > 11 ml-1). Of isolates, two different transversion mutations present 239th codon β-tubulin within three monophyletic groups Pythium spp. The lead same amino acid change from an ancestral cysteine serine (C239S), which coincides treated virulence assay, disease severity was not reduced on ethaboxam-treated for isolate aphanidermatum containing S239 but P. irregulare C239. queried publicly available sequences other search C239S represented our collection. This resulted taxa either homozygous or heterozygous C239S, including all genus Peronospora. Evidence presented herein supports hypothesis convergent evolution occurred without selection yet confers propose several hypotheses repeated mutation.