The widely used 35S promoter for plant systems is expressed comparatively weak in the moss Physcomitrella patens. In order to find more potent promoters, living moss protoplasts were transiently transfected with GFP and mCherry controlled by a test-promoter or 35S-promoter, respectively. The ratio of the two fluorescence intensity signals was used to determine the test-promoter strength.
This application note shows the assay performed in 96 well microplate format. The CLARIOstar® microplate reader detected a low number of GFP (>150) and mCherry (<100) transfected protoplasts. Furthermore, the strength of promoters compared to the 35S promotor could be determined and a stronger promotor for Physcomitrella patens was identified.
In contrast to establishing stable clones, which requires post-transfection expansion and selection, transient transfection offers a fast and economic method to compare promoter activation.