White locoweed toxicity is facilitated by a fungal endophyte and nitrogen-fixing bacteria

Mutualistic interactions with fungal endophytes and dinitrogen-fixing bacteria are known to exert key biological influences on the host plant. The influence of a fungal endophyte alkaloid on the toxicity of a plant has been documented in Oxytropis sericea. Oxytropis sericea is a perennial legume res...

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Published in:	Ecology (Durham) Vol. 88; no. 7; pp. 1850 - 1856
Main Authors:	Valdez Barillas, J.R, Paschke, M.W, Ralphs, M.H, Child, R.D
Format:	Journal Article
Language:	English
Published:	Washington, DC Ecological Society of America 01-07-2007
Subjects:	Animal and plant ecology Animal, plant and microbial ecology Applied ecology Ascomycota - metabolism Bacteria Biological and medical sciences Chemical ecology Ecotoxicology, biological effects of pollution Embellisia endophytes Endosymbionts Fundamental and applied biological sciences. Psychology Fungicides Fungicides, Industrial - pharmacology General aspects greenhouse experimentation indolizidine alkaloid inoculum Leaves microbial ecology mutualism Nitrogen Nitrogen Fixation nitrogen-fixing bacteria nodulation Nodules Oxytropis - drug effects Oxytropis - microbiology Oxytropis - toxicity Oxytropis sericea Pesticides phytotoxins Plant ecology Plant growth Plant Leaves - drug effects Plant Leaves - microbiology Plant Leaves - toxicity Plants plant–microbe interactions Rhizobium Rhizobium - physiology Root Nodules, Plant - drug effects Root Nodules, Plant - metabolism Root Nodules, Plant - microbiology Seeds - drug effects Seeds - microbiology Seeds - toxicity swainsonine Swainsonine - metabolism Swainsonine - toxicity Symbiosis Symbiosis Oxytropis sericea plant-microbe interactions Toxicity Interaction chemical ecology Ecology Rhizobium inclolizidine alkaloid Embellisia microbial ecology Fungi Alkaloid Plant swainsonine Nitrogen fixation Bacteria Endophyte Rhizobiaceae Microorganism Thallophyta
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Summary:	Mutualistic interactions with fungal endophytes and dinitrogen-fixing bacteria are known to exert key biological influences on the host plant. The influence of a fungal endophyte alkaloid on the toxicity of a plant has been documented in Oxytropis sericea. Oxytropis sericea is a perennial legume responsible for livestock poisoning in western North America. Livestock poisoning is attributed to the alkaloid swainsonine, which is synthesized inside the plant by the fungal endophyte Embellisia sp. In this study, the ability of Oxytropis sericea to form a dinitrogen-fixing symbiosis with Rhizobium and the effects of this symbiosis on the production of swainsonine by Embellisia sp. were evaluated in a greenhouse environment. Seeds of O. sericea were grown in plastic containers. Twenty-week-old O. sericea seedlings were inoculated with four strains of Rhizobium. Twenty weeks after inoculation, plant growth and root nodulation by Rhizobium were measured. Dinitrogen fixation was confirmed using an acetylene reduction assay (ARA) on excised root nodules. Dry leaves were analyzed for swainsonine content. A second set of plants was treated with fungicide to evaluate the effect of reduced fungal endophyte infection on plant growth and swainsonine production. All inoculated plants produced indeterminate nodules. The ARA indicated that 98% of the excised nodules were fixing dinitrogen. Rhizobium-treated plants had greater swainsonine concentrations than the non-inoculated controls. Plants that established from seeds treated with fungicide had lower biomass than non-fungicide-treated controls and plants treated with foliar fungicide. Plants treated with foliar fungicide and the controls had greater swainsonine concentrations than the plants that received seed fungicide. This greenhouse study is the first report of nodulation and dinitrogen fixation in O. sericea. It also demonstrates that dinitrogen fixation increases the production of swainsonine in O.jSericea plants infected with Embellisia sp. Results from this study suggest that dinitrogen fixation affects swainsonine production and has the potential to support the symbiosis between Embellisia sp. and O. sericea when soil nitrogen is limited. Oxytropis sericea competitiveness appears to be facilitated by an ability to simultaneously associate with Rhizobium and a fungal symbiont.
Bibliography:	http://hdl.handle.net/10113/8162 Corresponding Editor: J. N. Klironomos. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0012-9658 1939-9170
DOI:	10.1890/06-0728.1