Internuclear gene silencing in Phytophthora infestans

Transformation of the diploid oomycete plant pathogen Phytophthora infestan s with antisense, sense, and promoter-less constructs of the coding sequenc e of the elicitin gene inf1 resulted in transcriptional silencing of both t he transgenes and the endogenous gene. Since heterokaryons obtained by soma tic fusion of an inf1-silenced transgenic strain and a wild-type strain dis played stable gene silencing, inf1 silencing is dominant and acts in trans, Inf1 remained silenced in nontransgenic homokaryotic progeny from the sile nced heterokaryons, thereby demonstrating that the presence of transgenes i s not essential for maintaining the silenced status of the endogenous inf1 gene. These findings support a model reminiscent of paramutation and involv ing a trans-acting factor that is capable of transferring a silencing signa l between nuclei.