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The Melanin Biosynthesis Genes of Alternaria alternata Can Restore Pathogenicity of the Melanin-Deficient Mutants of Magnaporthe grisea

May 1997 , Volume 10 , Number  4
Pages  446 - 453

Chie Kawamura , 1 Jouji Moriwaki , 1 Norio Kimura , 1 Yasunari Fujita , 1 Shin-ichi Fuji , 2 Tetsuji Hirano , 2 Shinzo Koizumi , 3 and Takashi Tsuge 1

1School of Agricultural Sciences, Nagoya University, Chikusa, Nagoya 464-01, Japan; 2Aichi-Ken Agricultural Research Center, Nagakute-Cho, Aichi 480-11, Japan; 3Aichi-Ken Agricultural Research Center, Mountainous Region Experiment Farm, Inabu-Cho, Aichi 441-25, Japan

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Accepted 4 March 1997.

The phytopathogenic fungi Magnaporthe grisea and Alternaria alternata produce melanin via the polyketide biosynthesis, and both fungi form melanized colonies. However, the site of melanin deposition and the role of melanin in pathogenicity differ between these two fungi. M. grisea accumulates melanin in appressoria, and their melanization is essential for host penetration. On the other hand, A. alternata produces colorless appressoria, and melanin is not relevant to host penetration. We examined whether the melanin biosynthesis genes of A. alternata could complement the melanin-deficient mutations of M. grisea. Melanin-deficient, nonpathogenic mutants of M. grisea, albino (Alb¯), rosy (Rsy¯), and buff (Buf¯), were successfully transformed with a cosmid clone pMBR1 that carries melanin biosynthesis genes ALM, BRM1, and BRM2 of A. alternata. This transformation restored the melanin synthesis of the Alb¯ and Buf¯ mutants, but not that of the Rsy¯ mutant. The melanin-restored transformants regained mycelial melanization, appressorium melanization, and pathogenicity to rice. Further, transformation of Alb¯ and Buf¯ mutants with subcloned ALM and BRM2 genes, respectively, also produced melanin-restored transformants. These results indicate that the Alternaria genes ALM and BRM2 can restore pathogenicity to the mutants Alb¯ and Buf¯, respectively, due to their function during appressorium development in M. grisea.

Additional keywords: conidial melanization, conidiation, host-specific toxin, the Japanese pear pathotype of A. alternata.

© 1997 The American Phytopathological Society