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ARS Home » Midwest Area » Lexington, Kentucky » Forage-animal Production Research » Research » Publications at this Location » Publication #229629
Title: Loline Alkaloids: Currencies of Mutualism

Author
item SCHARDL, C - UNIVERSITY OF KENTUCKY
item GROSSMAN, R - UNIVERSITY OF KENTUCKY
item NAGABHYRU, J - UNIVERSITY OF KENTUCKY
item FAULKNER, U - UNIVERSITY OF KENTUCKY
item MALLIK, U - UNIVERSITY OF KENTUCKY

Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2007
Publication Date: 3/7/2007
Citation: Schardl, C.L., Grossman, R.B., Nagabhyru, J.R., Faulkner, U.P., Mallik, U.P. 2007. Loline Alkaloids: Currencies of Mutualism. Phytochemistry. 68:980-996. doi:10.1016/j.phytochem.2007.01.010

Interpretive Summary: University of Kentucky publication funded via a congressionally mandated SCA entitled "Continuation of Imroved Forage Livestock Production Systems (CRIS Number: 6440-21310-001-05S)".

Technical Abstract: Several species of Lolium and other cool-season grasses (Poaceae subfamily Pooideae) tend to harbor symbiotic, seed-transmitted, fungi that enhance their fitness by various means. These fungal endophytes – species of Neotyphodium or Epichloë (Clavicipitaceae) – are known for production of antiherbivore metabolites such as the bioprotective loline alkaloids. Lolines are saturated pyrrolizidines with an exo-1-amine and an ether bridge between C-2 and C-7. The ether bridge is an unusual feature for a biogenic compound in that it links two bridgehead carbon atoms. Much of the loline-biosynthetic pathway has been elucidated by administering isotopically labeled precursors to fungal cultures and by comparisons of loline biosynthesis genes to known gene families. The first step appears to be an unusual '-substitution reaction involving an enzyme related to O-acetylhomoserine (thiol) lyase, but which uses the secondary amine of l-proline rather than a sulfhydryl group as the nucleophile. The strained ether bridge is added after formation of the pyrrolizidine rings. Lolines with dimethylated or acylated 1-amines have insect antifeedant and insecticidal activities comparable to nicotine, but little or no toxicity to mammals. Considering the surprising abundance of lolines in some grass–endophyte symbiota, possible additional effects on plant stress tolerance and physiology are worth future consideration. In this review, we discuss the history of loline discovery, methods of analysis, biological activities and distribution in nature, as well as progress on the genetics and biochemistry of their biosynthesis, and on the chemical synthesis of these alkaloids.