Acquired resistance to mefenoxam in sensitive isolates of Phytophthora infestans

Abstract: The systemic fungicide mefenoxam has been important in the control of late blight disease caused by Phytophthora infestans. This phenylamide fungicide has a negative effect on the synthesis of ribosomal RNA, however, the genetic basis for inherited field resistance is still not completely clear. We recently observed that a sensitive isolate became tolerant after a single passage on mefenoxam-containing medium. Further analyses revealed that all sensitive isolates tested (in three diverse genotypes) acquired this resistance equally quickly. In contrast, isolates that were "resistant" to mefenoxam in the initial assessment (stably resistant) did not increase in resistance upon further exposure. However, there appeared to be a cost associated with acquired resistance in the initially sensitive isolates, in that isolates with acquired resistance grew more slowly on mefenoxam-free medium than did the same isolates that had never been exposed to mefenoxam. The acquired resistance of the sensitive isolates declined slightly with subsequent culturing on medium free of mefenoxam. To investigate the mechanism of acquired resistance, we employed strand-specific RNA sequencing. Many differentially expressed genes were genotype specific, but there was a set of genes differentially expressed in all genotypes. Among these were several genes (a phospholipase "Pi-PLD-like-3", two ATP binding cassette superfamily (ABC) transporters, and a mannitol dehydrogenase) which were up regulated and whose function might contribute to a resistance phenotype.

摘要：系统型杀菌剂咪鲜胺在控制由疫霉菌（Phytophthora infestans）引起的晚疫病方面发挥着重要作用。该苯酰胺类杀菌剂对核糖体RNA的合成产生负面影响，然而，对遗传性田间抗性的遗传基础的完全阐明尚不明确。我们最近观察到，一个敏感菌株在单一次在含有咪鲜胺的培养基上培养后，对其产生了耐受性。进一步分析揭示，所有测试的敏感菌株（在三种不同的基因型中）均以相同速度获得了这种抗性。相反，在初始评估中“对咪鲜胺具有抗性”的菌株，在进一步接触咪鲜胺后，其抗性并未增加。然而，似乎在最初敏感菌株获得抗性过程中存在一定的代价，即获得抗性的菌株在无咪鲜胺的培养基上生长速度比从未接触过咪鲜胺的同种菌株要慢。敏感菌株获得抗性在后续的无咪鲜胺培养基培养中略有下降。为了探究获得抗性的机制，我们采用了链特异性RNA测序。许多差异表达基因具有基因型特异性，但存在一组在所有基因型中差异表达的基因。其中，包括几个基因（一种磷脂酶“Pi-PLD-like-3”、两个ATP结合盒超家族（ABC）转运蛋白和一个甘露醇脱氢酶），这些基因被上调，其功能可能对产生抗性表型有所贡献。