Many different alkaloids have been isolated from tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] herbage, but amounts present are quite variable, and toxicity to consuming herbivores is not observed in every situation. All of the alkaloids have activity in selected bioassays and thus have been considered potential causal agents of animal disorders. Perloline, an alkaloid produced by the plant, and several other simple alkaloids were the first described in tall fescue, but they were not physiologically linked to signs of tall fescue toxicosis in livestock. Alkaloids associated with the fungal endophyte [Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin], namely loline and ergot alkaloids, accumulate in tall fescue herbage. Many of the signs of fescue toxicosis are similar to classic ergotism, and the ergot alkaloids produced by N. coenophialum are believed to be the principal cause of fescue toxicosis. The loline alkaloids are potent insect toxins but do not seem to be causative agents of fescue toxicosis. Peramine, which is an insect feeding deterrent, is present in endophyte infected tall fescue (E+), but in insignificant amounts. Biosynthesis of the fungal alkaloids and their genetic regulation have been elucidated nearly completely. Transgenic expression of the gene clusters for loline alkaloid biosynthesis could have applications for insect control in other agricultural plants. Exploiting grass-endophyte interactions to minimize the consumption of ergot alkaloids by livestock and to maximize insect-deterring benefits in the plant would remove significant limits to livestock productivity and promote the sustainability of tall fescue forage systems.
Keywords: perloline, peramine, unsaturated pyrroliyzidine alkaloids, ergot alkaloids.
Abbreviations: DMATrp, dimethylallyl tryptophan; DMAPP, dimethylallyl-diphosphate; draW, gene encoding for DMATrp synthase; KY-31, Kentucky 31 tall fescue; LPS1, LPS2, subunits of D-lysergyl peptide synthetase; lpsA, lpsB, encode for the LPS enzymes; NAL, N-acetylloline; NFL, N-formylloline; NRPS, non-ribosomal peptide synthetase; PPTase, phosphopantetheinyl transferase; Trp, tryptophan.
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