TRANSFORMATION OF BIPOLARIS-SOROKINIANA WITH THE GUS GENE AND USE FORSTUDYING FUNGAL COLONIZATION OF BARLEY ROOTS

Bipolaris sorokiniana, a fungal pathogen of cereals, was transformed w ith the GUS (beta-glucuronidase) gene, using a plasmid (pGUS5) contain ing GUS A with the constitutive promotor GPD-1 and a hygromycin-resist ance gene (hph) under the control of the same promotor. Hygromycin res istance was used as the selectable marker. Colonies growing on medium with hygromycin were obtained at a frequency of 6.5 X 10(-7) per viabl e fungal protoplast. Nineteen out of 20 tested hygromycin-resistant co lonies were also GUS positive. Transformants that showed a stable expr ession of GUS activity and hygromycin resistance after several conidia tion cycles and several months of growth on nonselective medium could be selected. However, some transformants lost their GUS activity and h ygromycin resistance after two conidiation cycles on nonselective medi um. The stable transformants did not differ from the wild-type strain in growth rate or pathogenicity. A significant, positive correlation w as found between GUS activity and ergosterol content and between GUS a ctivity and lesion size in barley roots infected with a transformed st rain. GUS activity could be detected in the root tissue before disease symptoms appeared, and only negligible background GUS activity was fo und in roots infected with the wild-type Fungus, These results indicat e that GUS-transformed strains of B. sorokiniana can be used for study ing fungal colonization and growth in plant tissue.