INTRODUCTIONHere we describe a protocol for transforming Oxyrrhis marina with FITC-labelled dextran (a DNA analog) by electroporation.\u00a0This protocol is reproducible, and results in a transformation efficiency of around 1%.We have confirmed the viability of transformed cells by allowing them to recover in the dark (and thus maintain fluorescence intensity) and then by observing fluorescent cells swimming normally, days after transformation (see the video\u00a0here).\u00a0NOTE ON AUTOFLUORESCENCEAlthough Oxyrrhis is a non-photosynthetic dinoflagellate and therefore lacks plastid autofluorescence, we have observed a small amount of green autofluorescence that is typically isolated in the anterior of the cell (See top panel of Figure 1).The autofluorescence was observed in wildtype cells, cells electroporated without FITC-dextran, and cells that were incubated with FITC-dextran but not electroporated. The autofluorescence was observed in cultures with both Dunaliella tertiolecta or heat-killed E. coli. The brightness and frequency of the autofluorescence also seemed to be dependent on culture conditions. Not all cells had the autofluorescence.ADDITIONAL INFORMATIONAs of yet we have been unable to demonstrate the actual uptake of plasmid DNA. We have tried using rhodamine labelled plasmids to demonstrate this but the results were inconclusive due to issues with cellular autofluorescence.\u00a0We have also tried this method with a variety of expression plasmids\u00a0encoding different promoters. For example, we tried the MOE promoter from\u00a0Perkinsus marinus\u00a0(a closely related species) and the generic eukaryotic CMV promoter. However no GFP fluorescence was detected in these samples.\u00a0We have also tried transforming\u00a0in vitro synthesized GFP encoding mRNA using this protocol. As of yet, no GFP production has been detected, but this may reflect non-cannonical translational systems in dinoflagellates as the same mRNA could be translated in starfish embryos.Although the development of expression systems in dinoflagellates remains a challenge, our results suggest that\u00a0O. marina may be amenable to genetic transformation.