Gene transfer in plant protoplasts Inhibition of gene activity by cytosine methylation and expression of single-stranded DNA constructs

Transfection of petunia protoplasts with the plasmid pUC118CaMVCAT, bearing the bacterial chloramphenicol acetyltransferase (CAT) gene, resulted in the appearance of CAT activity. No CAT activity was detected in protoplasts transfected with the hemimethylated form of pUC118CaMVCAT. Transfection of petunia protoplasts with ss DNA constructs bearing the coding and noncoding sequences of the CAT gene also resulted in the appearance of CAT activity, indicating expression of ss DNA constructs in transfected protoplasts. The relevance of our observations to control of gene expression in plant cells is discussed.