title: Antifungal mechanisms of ZnO and Ag nanoparticles to Sclerotinia homoeocarpa.
abstract: Fungicides have extensively been used to effectively combat fungal diseases on a range of plant species, but resistance to multiple active ingredients has developed in pathogens such as Sclerotinia homoeocarpa, the causal agent of dollar spot on cool-season turfgrasses. Recently, ZnO and Ag nanoparticles (NPs) have received increased attention due to their antimicrobial activities. In this study, the NPs' toxicity and mechanisms of action were investigated as alternative antifungal agents against S. homoeocarpa isolates that varied in their resistance to demethylation inhibitor (DMI) fungicides. S. homoeocarpa isolates were treated with ZnO NPs and ZnCl2(25-400 μg ml-1) and Ag NPs and AgNO3(5-100 μg ml-1) to test antifungal activity of the NPs and ions. The mycelial growth of S. homoeocarpa isolates regardless of their DMI sensitivity was significantly inhibited on ZnO NPs (≥200 μg ml-1), Ag NPs (≥25 μg ml-1), Zn2+ions (≥200 μg ml-1), and Ag+ions (≥10 μg ml-1) amended media. Expression of stress response genes, glutathione S-transferase (Shgst1) and superoxide dismutase 2 (ShSOD2), was significantly induced in the isolates by exposure to the NPs and ions. In addition, a significant increase in the nucleic acid contents of fungal hyphae, which may be due to stress response, was observed upon treatment with Ag NPs using Raman spectroscopy. We further observed that a zinc transporter (Shzrt1) might play an important role in accumulating ZnO and Ag NPs into the cells of S. homoeocarpa due to overexpression of Shzrt1 significantly induced by ZnO or Ag NPs within 3 h of exposure. Yeast mutants complemented with Shzrt1 became more sensitive to ZnO and Ag NPs as well as Zn2+and Ag+ions than the control strain and resulted in increased Zn or Ag content after exposure. This is the first report of involvement of the zinc transporter in the accumulation of Zn and Ag from NP exposure in filamentous plant pathogenic fungi. Understanding the molecular mechanisms of NPs' antifungal activities will be useful in developing effective management strategies to control important pathogenic fungal diseases.
authors.affiliation: Stockbridge School of Agriculture, University of Massachusetts, 161 Holdsworth Way, Amherst, MA 01003, United States of America. School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology, Wuhan 430070, People's Republic of China.
authors.forename: Junli
authors.initials: J
authors.lastname: Li
authors.forename: Hyunkyu
authors.initials: H
authors.lastname: Sang
authors.forename: Huiyuan
authors.initials: H
authors.lastname: Guo
authors.forename: James T
authors.initials: JT
authors.lastname: Popko
authors.forename: Lili
authors.initials: L
authors.lastname: He
authors.forename: Jason C
authors.initials: JC
authors.lastname: White
authors.forename: Om
authors.initials: O
authors.lastname: Parkash Dhankher
authors.forename: Geunhwa
authors.initials: G
authors.lastname: Jung
authors.forename: Baoshan
authors.initials: B
authors.lastname: Xing
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry / Q000494:pharmacology*; D001203:Ascomycota / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D025141:Drug Resistance, Fungal / Q000187:drug effects; D005656:Fungal Proteins / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D053758:Nanoparticles / Q000737:chemistry; D018384:Oxidative Stress; D010935:Plant Diseases / Q000382:microbiology; D012834:Silver / Q000737:chemistry / Q000494:pharmacology*; D015854:Up-Regulation; D015034:Zinc Oxide / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000935:Antifungal Agents; D002352:Carrier Proteins; D005656:Fungal Proteins; C017800:zinc-binding protein; D012834:Silver; D015034:Zinc Oxide