INFLUENCE OF BACTERIAL STRAIN GENOTYPE ON TRANSIENT EXPRESSION OF PLASMID DNA IN PLANT-PROTOPLASTS

It is demonstrated that transient expression of plasmid DNA in plant p rotoplasts can be strongly influenced by the bacterial strain used for plasmid propagation. Four different promoter constructs containing tw o light-responsive and two fungal elicitor-responsive parsley promoter s translationally fused to the reporter gene, beta-glucuronidase (GUS) , were amplified in bacterial strains MC1061, DH5alpha or GM2163 and t ested individually. Marked differences in basal expression levels and in fold inducibilities were observed upon transfection of parsley prot oplasts. Low levels of basal expression and strong light or elicitor i nducibilities were observed only with plasmid DNA derived from the met hylation-deficient GM2163 strain. In vitro methylation of DNA prior to transformation also drastically increased basal expression levels. Th e results suggest that DNA methylation may be partly responsible for d eregulating promoter activity in the transient expression system.