THE MELANIN BIOSYNTHESIS GENES OF ALTERNARIA-ALTERNATA CAN RESTORE PATHOGENICITY OF THE MELANIN-DEFICIENT MUTANTS OF MAGNAPORTHE-GRISEA

The phytopathogenic fungi Magnaporthe grisea and Alternaria alternata produce melanin via the polyketide biosynthesis, and both fungi form m elanized 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 essenti al for host penetration. On the other hand, A. alternata produces colo rless 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 A. grisea. Melanin-defi cient, nonpathogenic mutants of M. grisea, albino (Alb(-)), rosy (Rsy( -)), and buff (Buf(-)), were successfully transformed with a cosmid cl one 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, appres sorium melanization, and pathogenicity to rice. Further, transformatio n of Alb(-) and Buf(-) mutants with subcloned ALM and BRM2 genes, resp ectively, also produced melanin-restored transformants. These results indicate that the Alternaria genes ALM and BRM2 can restore pathogenic ity to the mutants Alb(-) and Buf(-), respectively, due to their funct ion during appressorium development in M. grisea.