In vitro formation of infection structures of Phytophthora infestans is associated with synthesis of stage specific polypeptides

Efficient and synchronized production of infection structures of Phytophthora infestans, the causal agent of late blight of potato, was established on an artificial membrane without the host plant. Microscopic comparison of the in vitro and the in planta formed fungal structures revealed a high degree of similarity. In vitro development of infection structures enabled detailed cytological and biochemical investigations. By video microscopy the highly dynamic phenomenon of cytoplasmic migration was monitored within the living fungus. At four distinct developmental stages, hyphae, cysts, germinating cysts and appressoria, all grown in vitro, protein synthesis was analysed by comparative two-dimensional SDS-polyacrylamide gel electrophoresis. On two-dimensional gels of protein extracts of the four developmental stages a number of polypeptides were identified that showed stage-specific differences in their relative amounts. The de novo synthesis of proteins was investigated by in vivo labelling experiments. A number of polypeptides showed development-dependent expression. The majority of changes in protein synthesis occurred during germination of cysts and development of the germ tubes. In particular, at the stage of appressoria formation, the actual start of the infection process, several major polypeptides were newly synthesized.