Assessing the Utility of Photoswitchable Fluorescent Proteins for Tracking Intercellular Protein Movement in the Arabidopsis Root

One way in which cells communicate is through the direct transfer of proteins. In plants, many of these proteins are transcription factors, which are made by one cell type and traffic into another. In order to understand how this movement occurs and its role in development, we would like to track this movement in live, intact plants in real-time. Here we examine the utility of the photoconvertible proteins, Dendra2 and (to a lesser extent) EosFP as tags for studying intracellular and intercellular protein movement in the Arabidopsis root. To this end, we made fusions between Dendra2 and six mobile transcription factors. Our results show that Dendra2 is an effective tool for studying protein movement between plant cells. Interestingly, we found that Dendra2 could not simply be swapped into existing constructs that had originally contained GFP. Most of the fusions made in this way failed to produce a fluorescent fusion. In addition we found that the optimal settings for photoconversion of Dendra2 in stably transformed roots were different from what has been published for photoconversion in transient assays in plants or in animal cells. By modifying the confocal setting, we were able to photoconvert Dendra2 in all cell layers in the root. However the efficiency of photoconversion was affected by the position of the cell layer within the root, with more internal tissues requiring more energy. By examining the Dendra2 fusions, we confirmed the mobility of the SHORT-ROOT (SHR) and CAPRICE (CPC) transcription factors between cells and we further discovered that SHR movement in stele and CPC movement in the epidermis are non-directional.