In planta comparative analysis of improved green fluorescent proteins with reference to fluorescence intensity and bimolecular fluorescence complementation ability

Green fluorescent protein (GFP) was discovered from the jellyfish Aequorea victoria, and several improvements have been carried out to change its physicochemical properties. The resulting improved GFP variants have been used as reporter proteins for bioimaging techniques in various research fields including plant science. Almost all GFP variants were developed using Escherichia coli to improve fluorescence properties in mammalian cells, but the impact in other organisms such as plant cells remains to be determined. In this study, we performed comparative analysis of four improved GFP variants, GFP-S65T, eGFP, frGFP and sfGFP, with reference to the fluorescence intensity in Arabidopsis protoplasts, and found that sfGFP is the brightest. Using non-fluorescent fragments from the GFP variants, we also conducted bimolecular fluorescence complementation (BiFC) assays to find appropriate fragment pairs of GFP-based BiFC for visualization of protein–protein interactions in living plant cells. Our observations revealed that the brightest is the sfGFP-based BiFC. Further, as an evaluation method for the sfGFP-based BiFC, a BiFC competition assay was successfully completed for the first time in planta. The present study provides useful information for selection and improvement of the GFP molecule and its application to BiFC technology in plants.