Avatar's Pandorian Botany in Reality
James Cameron's sci-fi classic Avatar was a long-waited one for movie fans and for me. The first time I watched it was a sophomore of Biochemistry major. On a personal note, this is one of the few movies I watched several times with my dad on TV. Not exactly from the beginning to end every time, but from a various starting point to the end. Fast forwarded a decade or slightly more than that, I became a plant biologist in the meantime and re-watching the movie brings completely different perspective.
The plot starts with the human race to obtain the mineral Unobtanium, which is available in the Pandora. Humans are inclined to have this mineral to solve the energy crisis of earth. But, the native Navi is the obstacle on their way. To conquer the Pandora and their mineral, humans made a base camp to observe them and even created a hybrid combining human and Navi's DNA.
That's the plot. But, watching that movie will make you realize that the Pondorian land is basically a forest, where Navi feels deep connection with the forest and a deep network of energy flows through living things. They explain the electro-chemical communication between the roots of tress, which acts like synapses between neurons and much more complex array of network than human brain. It is hard to miss those fascinating glowing plants at night, water containing plants, touch sensitive plants, and the tree of voice. Even, their most valuable mineral, Unobtanium, is basically under one giant tree, The Tree of Souls. Moreover, if you play the Avatar game, you will notice that a character can stop next to a tree in the forest and learn about that plant. If you observe the movie along the way, you will be amazed by the design of the movie set and arrangement of the forest and cool plants, which is absolutely impossible to design without in depth knowledge of plants. My hunch was right! When searched further about the design of the Avatar movie set, I found that the consultant for this movie set and story was a plant biologist, Jodie S. Holt, professor at University of California Riverside. That completely makes sense. She is the mastermind behind this amazing Pandorain botany.
In this blog post, among all those demonstrated cool plants in the movie, we will think about glowing plants from Pandora. When Jake and Neytiri were walking through the forest at night, they could easily find their way because of those glowing plants like nature's light. Isn't it fascinating? What if we had such plants in real life? Right—that would be awesome. We could use them at home, office, even in the street. It is not necessarily that we think about the option of glowing plants after watching the Avatar movie. The idea and development of Avatar's glowing plants has been in motion for a long time.
GUS reporter gene
The earliest system developed to visualize something inside a plant is based on the enzyme beta-glucuronidase expression. In this endeavor, gusA gene is inserted into a plasmid under different promoter or promoter of interest and eventually it produces the enzyme beta-glucuronidase, also known as GUS. After adding chromogenic compound X-gluc, chemical name is 5-bromo-4-chloro-3-indolyl glucuronide, as a substance, tissues producing beta-glucuronidase will turn blue. It helps to visualize in a spatial and temporal manner. It is an efficient system to understand the activity of promoter.
This amazing system was developed by Richard Anthony Jefferson as PhD student in the University of Colorado at Boulder. He applied this system in plants first and with that success the system had been adapted by several other systems as follow up. No wonder—the original research article has crossed 10k citation till date since its publication in 1987.
Expression of cell cycle marker, CyclinB1;1, with GUS in Arabidopsis root. Blue colored cells indicate the active mitosis activity. Source: Wu et al. Development (2010)
Like any other ground breaking system, GUS reporter system comes along with some limitations. The whole system is based on an enzyme, as a result it is only applicable to the system where the organism itself lacks beta-glucuronidase enzyme, such as plant, bacteria, algae, fungi. And, for the same reason the GUS expression system is not suitable for vertebrates. Even when we use it in suitable system it does not work magically. We have to incubate it 1 to 2 hours at 37 degree Celsius to make it works. Trade off is that—at 37 degree Celsius the staining works well, but cells are damaged at this temperature. As a result, after staining, we can't use the plant, literally we killed them during the staining process. Furthermore, the whole process is done in a non-sterile condition which has a possibility to let other unwanted organisms grow along with and if those organisms contain beta-glucuronidase enzyme, it will create artifact from the experimental data.
Luciferase from firefly
The next one in this list from beautiful firefly. In a pitch dark night, we see beautiful fireflies dancing around us with their flashing light on and off. Fireflies are not only something we observe in our daily life around us, but also it drew a great attention in arts and films, such as Isao Takahata's masterpiece movie Grave of the Fireflies.
This flashing light of fireflies is an excellent example of bioluminescence. It is named such a way, because the "luminescence" is produced using "biological" system or reaction. The simplest recipe for this reaction is oxygen, calcium, ATP (adenosine triphosphate), chemical luciferin in presence of the enzyme luciferase. The light produced by firefly is unique, unlike regular light bulb, they do not produce heat, otherwise they would destroy the organism due to additional heat.
In 1986, Ow et al. cloned firefly's luciferase gene and expressed into tobacco, Nicotiana tabacum, plants and when showering the plant with the substrate luciferin solution, it glows beautifully. This expression system is an useful tool for research in last few decades. But, is it helpful for creating the pandorian botany of glowing plants at night? The answer is a long one with logical arguments and debates. But, think simply, it requires a chemical substrate which we need to water over the plants to see the flash of luminescence.
How far we are from pandorian botany?
Probably—not too far. Just a quick reminder, our major challenge is to feed plants with exogenous chemical substrate. Recently, an article published in Nature Biotechnology, where authors tried to circumvent that issue. Unlike previous attempts, where genes were taken from bioluminescent bacterial or firefly, for making glowing plants; they have used the DNA from from bioluminescent fungi. In a different note, we should take a pause and appreciate the bounty of fungi. I have started to appreciate fungi more than ever recently after watching an amazing documentary, Fantastic Fungi.
Going back to the mechanism of recently developed glowing plants. Recently, we came to know about the fungal luciferin biosynthesis pathway and involved enzymes, which means it is possible to produce the substrate luciferin by expressing luciferin producing enzymes inside plants. Problem solved? Confusion lingers—what if the precursor for producing luciferin is not present in plants? The precursor for producing luciferin is caffeic acid. Caffeic acid is available in plants and they use it for lignin biosynthesis, an essential polymer for cell wall construction. With this idea, when researchers hijacked that system and express those four key genes for producing luciferin from caffeic acid and complete the cycle, they could produce tobacco plants with bioluminescence without external source of substrate.
Reminiscing of pandorian forest from the recently developed glowing plants
These glowing tobacco plants have visible light and it persists all along their life cycle with variable intensity. Moreover, if you keep a ripen banana close to the plants, it emits brighter light. Ripen banana produces ethylene gas, which is basically a hydrocarbon. It suggests that these plants will not only glow, but also can indicate the environmental cues. See the movie of recently glowing plants demonstrated above, which is reminiscing of the pandorian botany.
For uncountable reasons, plants are amazing. The way we utilize and manipulate plants for our use is more amazing than science fiction. This is why I am always fascinated by plants. On a personal note, my father's physical condition deteriorates continuously everyday. I wish to meet him soon someday and tell him the story how the glowing and glittering plants from James Cameron's movie Avatar is coming to our reality.
Thanks to Amber, a good friend and plant biology enthusiast, to read and edit the post.