With the rise of easy methods for creating and administering transgenes, there has been an exponential increase in genetically modified organisms. From crops which resist disease and tolerate drought, to viruses designed to deliver gene therapies to treat genetic disorders, scientists continue to push the boundaries of genetic manipulation. Recently published in Nature, Chin et al. present a genetically modified fluorescent petunia, bringing our society closer to a reality reminiscent of James Cameron’s Avatar.¹ The insertion of genes encoding fluorescent proteins into organisms has been employed for decades, mostly used for experimental purposes (i.e. reporter genes), but scientists have started to create fluorescent organisms for ornamental purposes. Most fluorescent organisms created thus far have been animals, for example brightly coloured aquarium fish or silkworms whose fluorescent silk can be used to create fluorescent textiles.^2,3 In the past, there have been experiments which created fluorescent plants by expressing a green fluorescent protein derived from the marine copepod Chiridius poppei (CpYGFP), but the fluorescence emitted was only visible under blue light excitation through a yellow emission filter.⁴ Since these plants had to be viewed under an emission filter, their usefulness as a fluorescent ornamental plant or as an experimental tool was limited. To circumvent this issue of fluorescent visibility, Chin et al. sought to produce ornamental plants using commercial Petunia hybrida cultivars expressing bright fluorescent flowers, excited by invisible UV light and visualized by the naked eye.¹

To produce these novel flowers, the team created an expression cassette containing a fluorescent protein (FP) gene called eYGFPuv – (a derivative of the CpYGFP protein excited by blue light) driven by the constitutive cauliflower mosaic virus (CaMV) 35S promoter.¹ The cassette also contained a transcriptional terminator from an Arabidopsis heat-shock protein, and the 5’UTR from an Arabidopsis cold-regulated gene.¹ This combination of genetic elements, expressed in triplicate via Agrobacterium-mediated transformation, allowed for the stable expression of the eYGFPuv FP throughout the plant.¹ Eighteen transgenic lines were created using the eYGFPuv FP, and one transgenic line was created with the eYGFP FP (also a CpYGFP derivative, excited by blue light) for comparison.¹ 

The authors started by examining fluorescence of calli (unorganized mass of cells) transformed with eYGFPuv and eYGFP, and saw that under UV light, fluorescence was only visible to the naked eye in calli containing eYGFPuv FP.¹ The team continued to grow the calli into mature plants and observed a maintenance of fluorescence throughout the whole plant.¹ Since one of the main purposes of the study was to obtain fluorescent flowers for display or observation-based experiments, fluorescence intensity was measured in the mature plants using photographs.¹ Again, the team only saw bright fluorescence under UV light, without emission filters in plants expressing eYGFPuv, showing the success of their novel gene construct.¹ To determine whether the novel construct could be used in other types of plants, the team inserted it into a more glamourous, double-flowered cultivar of P. hybrida and saw very similar results, suggesting the construct can potentially be applied to a wider range of species.¹

But fluorescence visible with the naked eye was not the only goal of this study – the team also aimed to maintain fluorescence under long exposure to UV, and properly characterize the genetic modifications induced in the plant.¹ They analyzed transgene copy number and found that some of their lines had multiple insertion events – potentially problematic for future commercialization of the product.¹ They also confirmed the fluorescence observed in their transgenic plants was indeed a result of the insertion of the FP transgene.¹ Importantly, there was no growth inhibition or morphological defects in the transgenic plants grown, suggesting neither UV exposure nor FP insertion causes damage to plants.¹ To further test this hypothesis, the team examined expression levels of the FP as well as anti-oxidative stress response genes in both transgenic and wild-type plants after two weeks of UVA exposure.¹ Results showed an increase in some anti-oxidative stress gene expression after UV exposure in both wild type and transgenic plants, suggesting all plants contain endogenous mechanisms to resist UV-induced damage.¹ The results also confirmed, at least in this study, that UV exposure does not cause growth inhibition, withering or fluorescence decay – important features for an ornamental plant.¹ 

Overall, the results from this study show a successful generation of bright fluorescence in P. hybrida plants, easily visualized under UV light, at the whole plant level.¹ Compared to previous work, the transgenic construct created by Chin et al. is leaps and bounds ahead, in terms of potential for commercial production.⁴ But this successful FP construct can also be used for plant research purposes as a reporter gene to study spatiotemporal relationships and behaviour of genes which are normally difficult to detect.¹ 

However, as fresh and promising as this research is, there are a few issues which need to be addressed in future work. First, some transgenic lines showed tessellated patterns of fluorescence expression in their leaves and flowers, as well as differing levels of expression between leaves and flowers, suggesting position effects regarding transgene insertion.¹ It is also possible that the CaMV 35S promoter was not constitutively activated in the plants used for this study, so further analyses and confirmations regarding position effects and gene activation are needed.¹ Second, although the plants in this study showed no adverse effects to prolonged UV exposure, further experimentation needs to be done on other species and in different conditions to properly confirm the lack of deleterious effects posed by UV exposure.¹

Currently, continued use of the eYGFPuv construct is taking place to create more varieties of fluorescent plants, for example, orchids and cyclamen.¹ As the method becomes more robust and ready for commercial production, the team will have to conduct an assessment of biodiversity impact of the transgenic plants, which has to be in accordance with domestic laws put in place by each jurisdiction or country.¹ This is often a difficult task to achieve (and the reason why many transgenic organisms never make it to commercial production), but since the petunia F1 hybrid cultivar is relatively self-incompatible, the plants undergo vegetative propagation, meaning they would not pose a threat to wild cultivars in terms of hybridization.¹

As a whole, this study puts forth a promising product, filling the gap in scientific advancement, and creating a plant that is both beautiful and useful. As briefly discussed in the paper, these fluorescent petunias also have the potential to be an engaging educational tool to help improve public perception and acceptance of genetically modified organisms.¹ With the current levels of scrutiny towards genetic modification, opening minds is a tall task, but an organism as incredible as this fluorescent petunia might just be the turning point we need for a productive future of (safe) genetic modification.