title: An Endophyte Constructs Fungicide-Containing Extracellular Barriers for Its Host Plant.
abstract: Surface cracks create sites for pathogen invasion. Yew trees (Taxus) hyperbranch from long-lived buds that lie underneath the bark [1], resulting in persistent bark cracking and deep air pockets, potentially allowing pathogens to enter the nutrient-rich vascular system (vertical phloem and inter-connected radial medullary rays [MR]). Yew is famous as the source of the anti-cancer diterpenoid drug Taxol. A mystery has been why both the tree and its resident non-pathogenic fungi (endophytes) synthesize Taxol, apparently redundantly [2-7]. These endophytes, as well as pure Taxol, suppress fungal pathogens including wood-decaying fungi (WDF) [8-11]. Here we show that a Taxol-producing fungal endophyte, Paraconiothyrium SSM001 [12], migrates to pathogen entry points including branch cracks. The fungus sequesters Taxol in intracellular hydrophobic bodies that are induced by WDF for release by exocytosis, after which the bodies can coalesce to form remarkable extracellular barriers, laced with the fungicide. We propose that microbial construction of fungicide-releasing hydrophobic barriers might be a novel plant defense mechanism. We further propose that the endophyte might be evolutionarily analogous to animal immune cells, in that it might expand plant immunity by acting as an autonomous, anti-pathogen sentinel that monitors the vascular system.
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada; David Geffen School of Medicine at UCLA, Los Angeles Biomedical Research Institute, Harbor-UCLA Medical Center, Torrance, CA 90502, USA.
authors.forename: Sameh S M
authors.initials: SS
authors.lastname: Soliman
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
authors.forename: John S
authors.initials: JS
authors.lastname: Greenwood
authors.affiliation: Department of Horticulture, Virginia Tech, Blacksburg, VA 24071, USA.
authors.forename: Aureliano
authors.initials: A
authors.lastname: Bombarely
authors.affiliation: SOL Genomic Network, Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, NY 14853-1801, USA.
authors.forename: Lukas A
authors.initials: LA
authors.lastname: Mueller
authors.affiliation: The Guelph Food Research Centre, Agriculture and Agri-Food Canada, Guelph, ON N1G 5C9, Canada.
authors.forename: Rong
authors.initials: R
authors.lastname: Tsao
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
authors.forename: Dick D
authors.initials: DD
authors.lastname: Mosser
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada. Electronic address: raizada@uoguelph.ca.
authors.forename: Manish N
authors.initials: MN
authors.lastname: Raizada
mesh_terms: D001203:Ascomycota / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D060026:Endophytes / Q000378:metabolism*; D008969:Molecular Sequence Data; D017239:Paclitaxel / Q000378:metabolism*; D020946:Taxus / Q000382:microbiology*; D014197:Trees / Q000382:microbiology*
chemical_list: D017239:Paclitaxel