Abstract
Indole-diterpenes are an important class of chemical compounds which can be unique to different fungal species. The highly complex lolitrem compounds are confined to Epichloë species, whilst penitrem production is confined to Penicillium spp. and Aspergillus spp. These fungal species are often present in association with pasture grasses, and the indole-diterpenes produced may cause toxicity in grazing animals. In this review, we highlight the unique structural variations of indole-diterpenes that are characterised into subgroups, including paspaline, paxilline, shearinines, paspalitrems, terpendoles, penitrems, lolitrems, janthitrems, and sulpinines. A detailed description of the unique biological activities has been documented where even structurally related compounds have displayed unique biological activities. Indole-diterpene production has been reported in two classes of ascomycete fungi, namely Eurotiomycetes (e.g., Aspergillus and Penicillium) and Sordariomycetes (e.g., Claviceps and Epichloë). These compounds all have a common structural core comprised of a cyclic diterpene skeleton derived from geranylgeranyl diphosphate (GGPP) and an indole moiety derived from tryptophan. Structure diversity is generated from the enzymatic conversion of different sites on the basic indole-diterpene structure. This review highlights the wide-ranging biological versatility presented by the indole-diterpene group of compounds and their role in an agricultural and pharmaceutical setting.
Highlights
Perennial ryegrass (Lolium perenne L.) is used for forage in temperate regions throughout the world including Northern Europe, Pacific North West of USA, Japan, South-eastern Australia, and New Zealand [1,2,3,4,5]
The indole-diterpenes are predominant in endophyte-infected perennial ryegrass and lolitrem B is the end-point of the complex indole-diterpene biochemical pathway (Figure 1) [12]
It was found that the reticulum and rumen muscles showed inhibition of normal electrical activity, which coincided with the induction of tremoring associated with skeletal muscle activity in penitrems, paxilline, and lolitrem B [33]
Summary
Perennial ryegrass (Lolium perenne L.) is used for forage in temperate regions throughout the world including Northern Europe, Pacific North West of USA, Japan, South-eastern Australia, and New Zealand [1,2,3,4,5]. Neurological signs associated with ryegrass staggers disease has been reported in animals, sheep, grazing on perennial ryegrass in Australia, New Zealand, as well as Pacific northwest of USA and Europe [13,14]. This imposes a negative impact on industry, dairy, meat, and wool production involving grazing animals [15]. Lolitrem B is the most abundant of the indole-diterpene series of compounds produced by perennial ryegrass endophytes belonging to Epichloë festucae var. Model assay showed good correlation to large animal models as seeds, deemed toxic through mouse studies, were neurotoxic to sheep that were orally fed with pellets containing the toxin [32]
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