Wirkung von Metalaxyl auf die Synthese von RNA, DNA und Protein in Phytophthora nicotianae

Abstract

Mctalaxyl is used to control discases caused by fungi of the order of the Perenosporales. We investigated the action of this fungicid eon nucleic acid and protein synthesis in liquid cultures of Phytophthora nicotianne.The uptake of 32P, 3H-uridine, 3H-thymidine and 14CC-leucine as precursors of nucleic acid and protein synthesis by the mycelium was not inhibited by metalaxyl.RKA synthesis as indicated by 3H-uridine incorporation was strongly inhibited (about 80%) by 0.3 pg/ml of metalaxyl. The inhibition was visible already few minutes after addition of t h r toxicant. Since the inhibition of incorporation of 3H-thymidine into DEA and of I4C-leucine into protein became significant 2 --3 hours later, we conclude that metalaxyl primarily interfers with XNA synthesis.Synthesis of ribosomal RNA is more affected (more than 90%) than that of tRNA (about 55%) and poly(A)-containing RNA. Since in the presence of actinomycin, in contrast to metalaxyl, protein synthesis is inhibited immediately as a consequence of complete inhibition of RNA synthesis and of the short life-time of mRNA, it is also evident that mRNA synthesis is less strongly inhibited, a t least during the early period of metalaxyl action.The molecular mechanism of metalaxyl inhibition of the transcription process remains open.The fungicide did not inhibit the activity of a partially purified RNA polymerase isolated from the filngus. On the other hand, the RNA synthesis (14C-UTP-incorporation) by a cell homogenate and by isolated nuclear fractions was inhibited significantly. Possibilities of the molecular action of metalaxyl are discussed. The RNA synthesis of some plant systems (cell cultures of Lycopersicon peruwianum, isolated nuclei from the same cell cultures, purified RNA polymerase from Spinacin oleracea chloroplasts) was not inhibited by metalaxyl, not even a t high concentrations.

Sequence diversity in the large subunit of RNA polymerase I contributes to Mefenoxam insensitivity in Phytophthora infestans

“…The RPAC40 subunit is in common with the RNApolIII complex that transcribes tRNAs. Strong changes in tRNA abundance were not the major effect of Metalaxyl (Wollgiehn et al ., ), and it is thus unlikely that SNPs in this subunit contribute significantly to conditioning insensitivity.…”

“…To avoid the influence of minor genes, and to circumvent the limitations of a small F1 population size, we exploited the existing evidence for the effects of Metalaxyl on oomycetes (Davidse et al ., , ; Wollgiehn et al ., ), and the availability of the P. infestans genome sequence (Haas et al ., ). Previously, a similar combination of biochemical evidence and phenotype, and candidate gene strategy, was used to identify the mode of action for the oomycete control chemical Mandipropamid (Blum et al ., ).…”

“…Biochemical assays using [ 3 H]uridine incorporation revealed a specific impact of Metalaxyl on the synthesis of RNA (Davidse et al ., , ) and, specifically, ribosomal RNA (rRNA) (Davidse et al ., ; Wollgiehn et al ., ). The syntheses of messenger and transfer RNAs (mRNA and tRNA, respectively) were affected to a lesser extent.…”

Sensitivity of wild-type and mutant Trichoderma harzianum strains tofungicides

“…Metalaxil is an inhibitor of RNA synthesis (Papavizas and Lewis, 1983;Wollgiehn et al, 1984). Mancozeb causes DNA damage and induces apoptosis (Calviello et al, 2006).…”

Analysis of RPA190 revealed multiple positively selected mutations associated with metalaxyl resistance in Phytophthora infestans

“…Metalaxyl, a phenylamide fungicide, inhibits the incorporation of 3 H‐uridine for the synthesis of ribosomal RNA . The fungicide has been used for four decades to control crop diseases caused by oomycetes such as Peronospora and Phytophthora including Phytophthora infestans (Mont) de Bary .…”