Temporal Transcriptional Pattern of Three Melanin Biosynthesis Genes, PKS1, SCD1, and THR1, in Appressorium-Differentiating and Nondifferentiating Conidia of Colletotrichum lagenarium.

A phytopathogenic fungus, Colletotrichum lagenarium, produces melanized appressoria that display temperature-sensitive differentiation. Conidia incubated in water at 24(deg)C germinated, and germ tubes differentiated into melanized appressoria. On the other hand, conidia incubated in water at 32(deg)C germinated and produced germ tubes that elongated without appressorium differentiation. Conidia in 0.1% yeast extract solution at 32(deg)C germinated and developed into vegetative hyphae. In this study, we investigated the temporal transcriptional pattern of cloned melanin biosynthesis genes, PKS1, SCD1, and THR1, in these differentiating and nondifferentiating conidia. During appressorium differentiation, de novo transcripts of the three melanin biosynthesis genes accumulated 1 to 2 h after the start of conidial incubation at 24(deg)C, and the amount of transcripts began to decrease at 6 h. In conidia germinating in water at 32(deg)C, the transcriptional pattern of the PKS1, SCD1, and THR1 genes was similar to that of these genes in appressorium-forming conidia, although no appressoria were formed. However, in conidia in 0.1% yeast extract solution at 32(deg)C, transcripts of the three melanin biosynthesis genes hardly accumulated.