Scytalone as a natural intermediate of melanin biosynthesis in appressoria of Colletotrichum lagenarium

Abstract

Melanin biosynthesis of appressoria in Colletotrichum lagenaru was studied using color mutants. Mutant 8015 of C. lagenarium obtained by N-methyl- N′-nitro- N-nitroso-guanidine treatment formed a red-brown colony and secreted a substance which restored black coloration to colonies of albino mutants. This substance was identified as scytalone (3,4-dihydro-3,6,8-trihydroxy-1(2H)naphthalenone). Nineteen albino mutants formed colorless appressoria, but in the presence of 0.75 m M scytalone, the albino mutants formed darkly pigmented appressoria indistinguishable from those of the parent strain. Furthermore, the time course of appressorial pigmentation of albino mutants in the presence of scytalone was the same as that of the parent strain. On nitrocellulose membranes and host cucumber cotyledons, the colorless appressoria of albino mutants germinated laterally to form secondary appressoria, and consequently had little ability to form penetration hyphae. In the presence of 0.75 m M scytalone, however, the pigmented appressoria penetrated nitrocellulose membranes and host cucumber cell walls similarly to those of the parent strain. From these results, we conclude that scytalone is a normal precusor of melanin in appressoria, and that appressorial pigmentation is essential for the formation of penetration hyphae in C. lagenarium.