Production of swainsonine by fungal endophytes of locoweed

Indolizidine and quinolizidine alkaloids

This review covers the isolation, structure determination, synthesis, chemical transformations and biological activity of indolizidine and quinolizidine alkaloids. Included in the review are the hydroxylated indolizidines lentiginosine, swainsonine, castanospermine and their analogues; alkaloids from animal sources, including ants, amphibians and beetles; indolizidine alkaloids from the genera Polygonatum, Prosopis and Elaeocarpus; indolizidine and phenanthroindolizidine alkaloids; alkylquinolizidine alkaloids, including myrtine, epimyrtine, plumerinine and Lycopodium metabolites; Lythraceae and Nuphar alkaloids; lupine alkaloids; and alkaloids from marine sources. 150 references are cited.

Biology and chemistry of endophytes

This review focuses on new endophyte-related findings in biology and ecology, and also summarises the various metabolites isolated from endophytes.

Herbivores cause a rapid increase in hereditary symbiosis and alter plant community composition

Microbial symbioses are ubiquitous in nature. Hereditary symbionts warrant particular attention because of their direct effects on the evolutionary potential of their hosts. In plants, hereditary fungal endophytes can increase the competitive ability, drought tolerance, and herbivore resistance of their host, although it is unclear whether or how these ecological benefits may alter the dynamics of the endophyte symbiosis over time. Here, we demonstrate that herbivores alter the dynamics of a hereditary symbiont under field conditions. Also, we show that changes in symbiont frequency were accompanied by shifts in the overall structure of the plant community. Replicated 25-m2 plots were enriched with seed of the introduced grass, Lolium arundinaceum at an initial frequency of 50% infection by the systemic, seed-transmitted endophyte Neotyphodium coenophialum. Over 54 months, there was a significantly greater increase in endophyte-infection frequency in the presence of herbivores (30% increase) than where mammalian and insect herbivory were experimentally reduced by fencing and insecticide application (12% increase). Under ambient mammalian herbivory, the above-ground biomass of nonhost plant species was reduced compared with the mammal-exclusion treatment, and plant composition shifted toward greater relative biomass of infected, tall fescue grass. These results demonstrate that herbivores can drive plant-microbe dynamics and, in doing so, modify plant community structure directly and indirectly.

The toxicosis of Embellisia fungi from locoweed (Oxytropis lambertii) is similar to locoweed toxicosis in rats1

Locoweeds cause significant livestock poisoning and economic loss in the western United States. The toxicity of Embellisia sp. fungi isolated from locoweed was compared with locoweed toxicity using the rat as a model. Rats were fed diets containing locoweed, fungus and alfalfa, or alfalfa. Locoweed- and fungus-fed rats consumed swainsonine-containing food at approximately 1.3 mg x kg(-1) x d(-1), gained less weight (P = 0.001) and ate less than controls. Swainsonine is the principal agent responsible for inducing locoism in animals. The concentrations of alkaline phosphatase and aspartate aminotransferase enzymes were greater (P < 0.05) in serum of locoweed- and fungus-fed rats compared with control rats. Similar intracellular vacuolation was observed in renal, pancreatic, and hepatic tissues of rats that consumed either locoweed or fungus. Rats that ate locoweed or Embellisia fungi displayed indistinguishable toxicity symptoms. The Embellisia fungi from locoweed can induce toxicity without the plants. Locoism management strategies need to involve management of the Embellisia fungi.

A community of unknown, endophytic fungi in western white pine

The endophytic fungi of woody plants may be diverse as often claimed, and likewise, they may be functionally novel as demonstrated in a few studies. However, the endophyte taxa that are most frequently reported tend to belong to fungal groups composed of morphologically similar endophytes and parasites. Thus, it is plausible that endophytes are known (i.e., described) parasites in a latent phase within the host. If this null hypothesis were true, endophytes would represent neither additional fungal diversity distinct from parasite diversity nor a symbiont community likely to be novel ecologically. To be synonymous with parasites of the host, endophytes should at least be most closely related to those same parasites. Here we report that seven distinct parasites of Pinus monticola do not occur as endophytes. The majority of endophytes of P. monticola (90% of 2,019 cultures) belonged to one fungal family, the Rhytismataceae. However, not a single rhytismataceous endophyte was found to be most closely related by sequence homology to the three known rhytismataceous parasites of P. monticola. Similarly, neither endophytic Mycosphaerella nor endophytic Rhizosphaera isolates were most closely related to known parasites of P. monticola. Morphologically, the endophytes of P. monticola can be confounded with the parasites of the same host. However, they are actually most closely related to, but distinct from, parasites of other species of Pinus. If endophytes are generally unknown species, then estimates of 1 million endophytes (i.e., approximately 1 in 14 of all species of life) seem reasonable.