Transformation of the Oomycete Saprolegnia monoica to hygromycin-B resistance

Saprolegnia monoica was stably transformed to hygromycin resistance using the plasmids pTH210 and pHAM34H containing a bacterial phosphotransferase gene fused to regulatory sequences from genes of another Oomycete. Vectors pBT6, pCM54, used to transform higher fungi, yielded no stable transformants. DNA hybridizations indicated that transformation resulted from a single-copy integration of the transforming vector. Development of non-resistant subcultures from transformed colonies revealed that the transgene could become silent and was not uniformly expressed in the transformants.