title: A zinc-binding citrus protein metallothionein can act as a plant defense factor by controlling host-selective ACR-toxin production.
abstract: Metallothionein is a small cysteine-rich protein known to have a metal-binding function. We isolated three different lengths of rough lemon cDNAs encoding a metallothionein (RlemMT1, RlemMT2 and RlemMT3), and only RlemMT1-recombinant protein had zinc-binding activity. Appropriate concentration of zinc is an essential micronutrient for living organisms, while excess zinc is toxic. Zinc also stimulates the production of host-selective ACR-toxin for citrus leaf spot pathogen of Alternaria alternata rough lemon pathotype. Trapping of zinc by RlemMT1-recombinant protein or by a zinc-scavenging agent in the culture medium caused suppression of ACR-toxin production by the fungus. Since ACR-toxin is the disease determinant for A. alternata rough lemon pathotype, addition of RlemMT1 to the inoculum suspension led to a significant decrease in symptoms on rough lemon leaves as a result of reduced ACR-toxin production from the zinc trap around infection sites. RlemMT1-overexpression mutant of A. alternata rough lemon pathotype also produced less ACR-toxin and reduced virulence on rough lemon. This suppression was caused by an interruption of zinc absorption by cells from the trapping of the mineral by RlemMT1 and an excess supplement of ZnSO(4) restored toxin production and pathogenicity. Based on these results, we propose that zinc adsorbents including metallothionein likely can act as a plant defense factor by controlling toxin biosynthesis via inhibition of zinc absorption by the pathogen.
authors.affiliation: Kagawa University, Miki, Kagawa 761-0795, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nishimura
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tatano
authors.forename: Yoko
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Kouhei
authors.initials: K
authors.lastname: Ohtani
authors.forename: Takeshi
authors.initials: T
authors.lastname: Fukumoto
authors.forename: Kenji
authors.initials: K
authors.lastname: Gomi
authors.forename: Yasuomi
authors.initials: Y
authors.lastname: Tada
authors.forename: Kazuya
authors.initials: K
authors.lastname: Ichimura
authors.forename: Kazuya
authors.initials: K
authors.lastname: Akimitsu
mesh_terms: D000528:Alternaria / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002957:Citrus / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D003001:Cloning, Molecular; D018744:DNA, Plant / Q000235:genetics; D005800:Genes, Fungal; D017343:Genes, Plant; D054884:Host-Pathogen Interactions / Q000235:genetics / Q000502:physiology; D008668:Metallothionein / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009183:Mycotoxins / Q000096:biosynthesis*; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014774:Virulence; D015032:Zinc / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018744:DNA, Plant; D009183:Mycotoxins; D010940:Plant Proteins; D011994:Recombinant Proteins; C017800:zinc-binding protein; D008668:Metallothionein; D015032:Zinc