Takano Y, Kubo Y, Kawamura C, Tsuge T, Furusawa I
Faculty of Agriculture, Kyoto University, Kyoto, 606-01, Japan
Fungal Genet Biol. 1997 Feb;21(1):131-40.
Colletotrichum lagenarium and Alternaria alternata produce a dark pigment, melanin. The C. lagenarium PKS1 and A. alternata ALM genes are involved in polyketide synthesis in the melanin biosynthesis pathway. PKS1 encodes a type I polyketide synthase. For functional comparison of the ALM gene with the PKS1 gene, we examined whether the A. alternata ALM gene could restore melanin synthesis in C. lagenarium albino mutant (Pks1(-)). The ALM gene transformed the albino mutant (Pks1(-)) to melanin-producing phenotypes, designated CAL transformants. The pigment intensity of both melanized colonies and appressoria of CAL transformants was weaker than that of the wild type. Ultrastructural studies of the cell walls of appressoria demonstrated that CAL transformants formed an outer melanized layer, as did the wild type. On the other hand, the thin inner and middle layers were less electron-dense than those of the wild type. CAL transformants were able to penetrate cellulose membranes as effectively as the wild type. By contrast, the penetration frequency of CAL transformants on cucumber cotyledons was remarkably reduced compared to that of the wild type. During conidial germination, the PKS1 transcript accumulated de novo in both the wild-type and CAL transformants after the start of conidial incubation. On the other hand, ALM transcript accumulated in conidia of CAL transformants before the start of conidial incubation.
葫芦炭疽菌和链格孢会产生一种深色色素——黑色素。葫芦炭疽菌的PKS1基因和链格孢的ALM基因参与黑色素生物合成途径中的聚酮化合物合成。PKS1编码一种I型聚酮化合物合酶。为了对ALM基因和PKS1基因进行功能比较，我们检测了链格孢的ALM基因是否能恢复葫芦炭疽菌白化突变体（Pks1(-)）中的黑色素合成。ALM基因将白化突变体（Pks1(-)）转化为产生黑色素的表型，命名为CAL转化体。CAL转化体的黑色素化菌落和附着胞的色素强度均弱于野生型。对附着胞细胞壁的超微结构研究表明，CAL转化体与野生型一样形成了外层黑色素化层。另一方面，其薄的内层和中层电子密度低于野生型。CAL转化体能够与野生型一样有效地穿透纤维素膜。相比之下，CAL转化体在黄瓜子叶上的穿透频率与野生型相比显著降低。在分生孢子萌发过程中，分生孢子培养开始后，野生型和CAL转化体中PKS1转录本均重新积累。另一方面，CAL转化体分生孢子在分生孢子培养开始前就积累了ALM转录本。
