A fungal endophyte induces transcription of genes encoding a redundant fungicide pathway in its host plant
1 Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada
2 Faculty of Pharmacy, Zagazig University, Zagazig, Egypt
3 Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
4 The Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, ON N1G 5C9, Canada
BMC Plant Biology 2013, 13:93 doi:10.1186/1471-2229-13-93Published: 26 June 2013
Taxol is an anti-cancer drug harvested from Taxus trees, proposed ecologically to act as a fungicide. Taxus is host to fungal endophytes, defined as organisms that inhabit plants without causing disease. The Taxus endophytes have been shown to synthesize Taxol in vitro, providing Taxus with a second potential biosynthetic route for this protective metabolite. Taxol levels in plants vary 125-fold between individual trees, but the underlying reason has remained unknown.
Comparing Taxus trees or branches within a tree, correlations were observed between Taxol content, and quantity of its resident Taxol-producing endophyte, Paraconiothyrium SSM001. Depletion of fungal endophyte in planta by fungicide reduced plant Taxol accumulation. Fungicide treatment of intact plants caused concomitant decreases in transcript and/or protein levels corresponding to two critical genes required for plant Taxol biosynthesis. Taxol showed fungicidal activity against fungal pathogens of conifer wood, the natural habitat of the Taxol-producing endophyte. Consistent with other Taxol-producing endophytes, SSM001 was resistant to Taxol.
These results suggest that the variation in Taxol content between intact Taxus plants and/or tissues is at least in part caused by varying degrees of transcriptional elicitation of plant Taxol biosynthetic genes by its Taxol-producing endophyte. As Taxol is a fungicide, and the endophyte is resistant to Taxol, we discuss how this endophyte strategy may be to prevent colonization by its fungal competitors but at minimal metabolic cost to itself.