First published online May 21, 2004; 10.1105/tpc.021279
The Plant Cell 16:1575-1588 (2004)
© 2004 American Society of Plant Biologists
A Fungal Metallothionein Is Required for Pathogenicity of Magnaporthe grisea
Sara L. Tuckera,1,
Christopher R. Thorntona,
Karen Taskerb,
Claus Jacobb,
Greg Gilesb,
Martin Egana and
Nicholas J. Talbota,2
a School of Biological Sciences, University of Exeter, Washington Singer Laboratories, Exeter EX4 4QG, United Kingdom
b School of Chemistry, University of Exeter, Exeter, EX4 4QD, United Kingdom
2 To whom correspondence should be addressed. E-mail n.j.talbot{at}exeter.ac.uk; fax 44-1392-264668.
The causal agent of rice blast disease, the ascomycete fungus Magnaporthe grisea, infects rice (Oryza sativa) plants by means of specialized infection structures called appressoria, which are formed on the leaf surface and mechanically rupture the cuticle. We have identified a gene, Magnaporthe metallothionein 1 (MMT1), which is highly expressed throughout growth and development by M. grisea and encodes an unusual 22amino acid metallothionein-like protein containing only six Cys residues. The MMT1-encoded protein shows a very high affinity for zinc and can act as a powerful antioxidant. Targeted gene disruption of MMT1 produced mutants that show accelerated hyphal growth rates and poor sporulation but had no effect on metal tolerance. Mmt1 mutants are incapable of causing plant disease because of an inability to bring about appressorium-mediated cuticle penetration. Mmt1 appears to be distributed in the inner side of the cell wall of the fungus. These findings indicate that Mmt1-like metallothioneins may play a novel role in fungal cell wall biochemistry that is required for fungal virulence.
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