Kawamura C, Moriwaki J, Kimura N, Fujita Y, Fuji S, Hirano T, Koizumi S, Tsuge T
School of Agricultural Sciences, Nagoya University, Japan.
Mol Plant Microbe Interact. 1997 May;10(4):446-53. doi: 10.1094/MPMI.1997.10.4.446.
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 pMRB1 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.
植物病原真菌稻瘟病菌（Magnaporthe grisea）和链格孢（Alternaria alternata）通过聚酮生物合成途径产生黑色素，且这两种真菌都能形成黑色素化的菌落。然而，这两种真菌中黑色素的沉积部位以及黑色素在致病性中的作用有所不同。稻瘟病菌在附着胞中积累黑色素，其黑色素化对于侵入宿主至关重要。另一方面，链格孢产生无色附着胞，黑色素与侵入宿主无关。我们研究了链格孢的黑色素生物合成基因是否能互补稻瘟病菌的黑色素缺陷突变。用携带链格孢黑色素生物合成基因ALM、BRM1和BRM2的黏粒克隆pMRB1成功转化了稻瘟病菌的黑色素缺陷型非致病突变体，即白化（Alb-）、玫瑰色（Rsy-）和浅黄色（Buf-）突变体。这种转化恢复了Alb-和Buf-突变体的黑色素合成，但未恢复Rsy-突变体的黑色素合成。黑色素恢复的转化体重新获得了菌丝体黑色素化、附着胞黑色素化以及对水稻的致病性。此外，分别用亚克隆的ALM和BRM2基因转化Alb-和Buf-突变体，也产生了黑色素恢复的转化体。这些结果表明，链格孢基因ALM和BRM2分别能恢复Alb-和Buf-突变体的致病性，这是由于它们在稻瘟病菌附着胞发育过程中的功能所致。
