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      Loline alkaloids: Currencies of mutualism.

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          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 gamma-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.

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          Author and article information

          Journal
          Phytochemistry
          Phytochemistry
          Elsevier BV
          0031-9422
          0031-9422
          Apr 2007
          : 68
          : 7
          Affiliations
          [1 ] Department of Plant Pathology, 201F Plant Science Building, 1405 Veterans Drive, University of Kentucky, Lexington, KY 40546-0312, USA.
          Article
          S0031-9422(07)00049-0
          10.1016/j.phytochem.2007.01.010
          17346759
          ce01fcfd-3275-4cff-b00b-fbd796e4acdd
          History

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