In-vitro and in-vivo nematicidal activities of the cyclic dodecapeptide omphalotin A

Abstract

: Omphalotin A, a cyclic dodecapeptide produced by submerged cultures of the basidiomycete Omphalotus olearius, exhibited in-vitro and in-vivo nematicidal activity. Meloidogyne incognita was the most sensitive nematode. At 2.0 mg litre-1, 50% of the nematodes were dead after one hour. Heterodera schachtii, Radopholus similis and Pratylenchus penetrans were aþ ected at higher concentrations. Incorporated into agar, the compound prevented infection of cucumber seedlings by M. incognita at concentrations of 1 mg litre-1 and higher. In glasshouse tests, complete protection of cucumbers and lettuce was achieved between 2.5 and 10 mg litre-1. No insecticidal activity was observed when Plutella xylostella, Phaedon cochleariae or Spodoptera frugiperda were fed material containing 4 g kg-1 of omphalotin A.1999 Society of Chemical Industry (

Exploring fungal RiPPs from the perspective of chemical ecology

“…Produced by the fungus Omphalotus olearius [ 38 , 39 ] , omphalotins were discovered during a search for fungal metabolites showing nematocidal activity against Meloidogyne incognita [ 39 ]—a plant parasitic nematode capable of targeting at least 1098 species [ 40 – 43 ]. Examination of the omphalotins revealed their extremely selective nature towards M. incognita [ 44 ], albeit with reduced specificity at increased concentrations [ 45 ]. Originally omphalotins were believed to be produced by an NRPS, however such a gene could not be identified within the genome sequence of O. olearius .…”

“…Since omphalotin is not secreted from the fungus into the surrounding environment [ 39 ], the toxic action of the peptide may only be realised if the fungus is consumed, once again indicating a RiPP’s function to be in defence against mycophagy. In contrast to the basidiocarp localisation of RiPPs in the majority of amatoxin-producing species [ 45 , 76 , 77 ], the omphalotin peptide is located in the fungal mycelia rather than the fruiting body of the fungus [ 47 , 83 ] despite its high visibility (Fig. 3 C).…”

Cyclic Ribosomal Peptides from Eukaryotes

“…(borosins)が RiPPs として報告されている (21) ． これら真菌由来 RiPPs も様々な生理活性を示す．テン グタケは致死性の高い毒キノコだが，それはα-amanitin および類縁体(amatoxins)が持つ RNA ポリメラーゼ II 阻害活性による．Phallacidin およびその類縁体(phallotoxins)は F-アクチンに結合して重合を阻害する．Ustiloxin と phomopsin は微小管の vinca ドメインに結合し て重合を阻害する (22) ．オート麦感染性病原真菌により 産生される victorin は，宿主の酸化還元酵素チオレドキ シンに結合して病原性を発揮する (23) ．Omphalotin は植 物寄生線虫であるネコブセンチュウに対する強い選択的 殺虫活性を示す (24) ．なお，植物共生真菌が産生する epichloëcyclin は植物感染時に多量に産生されるが，その 生物学的機能は不明である． 現在のところ，キノコからは head-to-tail 型のみ，カ ビからは side-chain 型のみが知られているのに対し，植 物からは head-to-tail 型の cyclotides (25) や orbitides (26) に加 えて，最近 side-chain 型のものが多数報告された (27,28) ．…”