Texas, USA 2010 - International Herbage Seed Group

Chemical diversity of bioprotective alkaloids of endophytic fungi in coolseason grassesC.A. Young, S. Mittal & J.E. TakachForage Improvement Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401cayoung@noble.orgAbstractEpichloë endophytes (Epichloë and Neotyphodium species) are important fungal symbionts thatform mutualistic symbioses with cool season grasses. The asexual Neotyphodium species havebeen utilized in agriculture to enhance the persistence of grasses such as tall fescue and perennialryegrass. These fungi are known to produce a range of bioprotective alkaloids, peramine, lolines,ergot alkaloids and lolitrems (indole-diterpenes) that provide anti-insect and anti-mammalianproperties that protect their host. Of most interest in the agricultural setting are endophyte/grassassociations that produce only the beneficial anti-insect alkaloids. Methodologies are wellestablished to detect and quantify the presence of these alkaloids. More recently the genesrequired for the biosynthesis of the four bioprotective alkaloids have been cloned andcharacterized from a number of endophytes present in agriculturally important grasses. As foundwith other fungal secondary metabolite biosynthesis genes, the genes for three of the fouralkaloids (ergot alkaloids, indole-diterpenes and lolines) are present in co-regulated geneclusters. This genomic organization enabled the identification of sets of genes that are likely tobe involved in the biosynthesis of each alkaloid. The cloning and characterization of thesealkaloid biosynthesis genes now provides an opportunity to understand the biochemicalpathways by means of targeted mutagenesis and determine metabolite diversity across naturallyoccurring endophytes based on the presence and absence of genes.IntroductionEndophytes (microorganisms that colonize plants) are found everywhere in nature, but many ofthese associations are not fully understood (Rodriguez & Redman, 2008). However,clavicipitaceous fungi are known to inhabit cool season grasses and these fungal endophyteshave been well studied for a number of decades in agriculturally important forages (Bacon et al.,1977; Sampson, 1933). The Epichloae broadly consists of the sexual Epichloë and asexualNeotyphodium species that systemically infect the aerial parts of the grass plant. They are knownto aid with the general persistence of the plant and have been deemed akin to a “supergene”because of the growth advantage they provide their host.In the 1930s a tall fescue cultivar “Kentucky 31” had shown great promise with persistenceespecially during times of drought (reviewed in Bacon, 1995). What was not understood at thetime was that a systemic infection of the fungus Neotyphodium coenophialum provided the grasswith persistence (Bacon et al., 1977). Unfortunately, this same fungus also gave Kentucky 31 abad name due to the poor animal performance and reproductive problems that it caused grazinglivestock (reviewed in Bacon, 1995). Kentucky 31 had an even greater effect on horses inKentucky – a state that prides itself on an extensive thoroughbred industry – triggering a great129