Tobacco Glowers – A trip up the Na’vi into the Heart of Lightness

April 28, 2020 | Jim Lane

Today, we start with Lucifer, as in the devil (who is supposed to be in the details). He plays a role in these details, for sure, because there is this substance called luciferin, which you find in certain species of fungi, though not your everyday ‘shrooms. It causes them to glow, and if you find yourself suddenly with visions of a journey down the Na’vi River at Animal Kingdom in Disney World, you’re actually not far off.

Some strange fungi and strange weird animals such as deep-sea creatures including lampfish. Bacteria have this capacity, as do fireflies. Firefly luciferin is found in some beetle species, and they use it to attract mates.

For many years, scientists have been pursuing a technology that would lend luminescence to plants, or even animals, in a way that we could target and control. Lampfish on land, if you will.

A team of scientists led by researchers at Planta LLC, and the Institute of Bioorganic Chemistry at the Russian Academy this week have reported in Nature Biotechnology that they have inserted bioluminescence in a new way that commands attention.

For years, the basic idea was to take the bacterial genes and insert them into the plastids. Plastids? These are small membrane-bound organelles that reside inside the cells of plants, algae and some other organisms, and include chloroplasts that trap sunlight energy and enable photosynthesis.

It is believed that chloroplasts are very ancient cyanobacteria that were trapped inside a very ancient ancestor of ours, about 1.5 billion years ago, and thereby our line of the Tree of Life, the eukaryotes, gained the ability to photosynthesize and thereby populate the world. Lucky us.

We humans don’t have plastids, and that’s why we have to eat food instead of living peacefully like plants through photosynthesis. We do have organelles, many of them. In fact, we have mitochondria inside us that enable energy production from the oxidation of sugars and the release of a substance called ATP. That cycle powers you, and every living thing large enough to see. Just like chloroplasts, it is believed that the mitochondria represent a bacteria that was captured and ingested by an ancestor of ours more than a billion years ago. The two organisms, the ingested mitochondria and our ancestor, became symbionts, cooperating to survive and sharing mutually supportive capabilities.

This tour down the ancient hallways of pre-historic science becomes important at this moment. Let’s return to the main narrative, the problem scientists had when they tried to insert these bacterial genes into the plastids. The result — it works, sort of. You just get a very low light level, too low to be useful. A candle in the wind, so to speak, or perhaps better, a candle seen across an ocean.

You see, our plastid friends are very important and useful — where would plants be without photosynthesis and where would we be without our veggies? Yet, our host organisms (and plants) evolved an important biological cycle that the plastids don’t have.

It involves our old friend lignin, of which it is often said that you can make anything out of lignin except money.

How do plants make lignin, which give them strength and rigidity and make trees trees instead of limp noodles? In part, we can thank something called the caffeic acid cycle and the phenylpropanoid pathway. That pathway is the one by which plants make lignin, and some other important substances.

Making plants glow for real

This scientific team have inserted bioluminescence into that very pathway, and it works reasonably well as a lab experiment as a means of achieving plants that have the ability to glow.

They write:

The caffeic acid cycle, which is a metabolic pathway responsible for luminescence in fungi, was recently characterized.

We report light emission in Nicotiana tabacum and Nicotiana benthamiana plants without the addition of any exogenous substrate by engineering fungal bioluminescence genes into the plant nuclear genome.

We engineered tobacco plants with a fungal bioluminescence system that converts caffeic acid (present in all plants) into luciferin and report self-sustained luminescence that is visible to the naked eye. Moreover, the green luminescence produced by the caffeic acid cycle fits well with the optical transparency window of pigmented plant tissues.

Our findings could underpin development of a suite of imaging tools for plants.

Could it be applied to humans or animals? Will cats ever glow?

The scientists write: Although caffeic acid is not native to animals, autonomous luminescence could also be enabled in animals by including two additional enzymes.

More about Planta

The founders write:

We created Planta in 2017 to make glowing plants. We are not the first to attempt this, but we have the right technology — an entirely novel bioluminescent design created by our team. With our expertise in molecular technologies and plant transgenesis, we are developing bright self-luminous plants.

What can you do with a glowing plant?

The founders of Planta report that they “intend to introduce ornamental plants within the next two years and commercialize these in global markets.”

About phenotyping

Generally, people know a lot more about genotyping than we do about phenotyping. You may have had your DNA analysis done — that’s genotype. But when a service made predictions about health — are you more likely to have a disease, and so forth, that’s more about how your genome interacts with your environment, and that’s phenotype. If your twin smokes three packs of cigarettes a day, gains lots of weight, never exercises and spends hours baking in sunlight without any skin protection, you’ll probably look a lot different at age 65 (if your twin survives that long). There’s no real difference in your genotype, but a big difference in your phenotype.

How we handle stress is one thing. How plants we grow for crops handle their stresses — dust, drought, toxins, damp, cold — all yield-killers. These are phenotypic responses, because it is the genome interacting to the environment.

Researchers at Johns Hopkins offer this explanation:

Identification of a protein gene product and determination of its function as a receptor, ligand, or enzyme is a proximal goal. Understanding the role of the gene and its product in the context of a living organism is the ultimate goal. Phenotyping evaluations can combine in vivo evaluations, imaging strategies, and clinical and anatomic pathology to characterize complex phenotypes.

What can you do with a plant the glows, besides use it ornamentally?

For one, it becomes very easy to spot plants when they have a bit of glow to them, and it’s easy to train machines to spot them as well. When you introduce a trait, you can track that plant if that trait is always present in a luminescent plant. Pretty easy to spot if the glowing plants are growing teller than the non-glowing ones, which makes it easier to do field trials and measure results.

Plus, when you have a modified organism, if it glows (even if only slightly), it’s pretty easy to spot when someone is using your organism without your permission. It’s the Rudolph the Red Nosed Microbe.

Biomarkers that are visual are used in therapeutics, but typically we use radioactive material to do the trick, and if you have a friend or loved one who’s gone through a PET or SPECT scan, you know all about it.

Farther out there in the world of wow

Think of it this way. Bioluminescence is a very interesting phenomenon, because you can produce photons at night using the photons that were harvested from the sun in the daytime. It sort of extends the sunlight clock, if you think about it.

One of the things that we find regrettable about the world of plants, here in Digestville, is that they are really poor users of sunlight. Plants absorb between 2-8 percent of the sunlight that’s shining on them. Bottom line, if they could utilize more light, they could run photosynthesis on a more industrial scale, absorb a lot more CO2 from the atmosphere and produce a lot more food, or fuel or fiber, per acre of land. All interesting capabilities.

One of the reasons that plants use light so inefficiently is that they don’t like ultraviolet and infrared light. We don’t like it much either — that’s where all the skin damage and sunburn and sun poisoning comes from, and it’s one of the reasons we get sick from radiation. Neither they nor you can benefit much from the radio spectrum used for microwaves, mobile and cordless phones, Bluetooth, AM radio, over-the-air TV, suntanning or X-rays.

What’s very interesting about bioluminescence, is that if you take fireflies as an example, they only emit visible light, in the green to yellow range, more or less. Not much point in attracting a mate with an invisible wavelength. So, the light that is emitted through this process is safer and very efficient for plants, much more so than actual sunlight or ultraviolet light sometimes used by growers.

Now, green light isn’t very useful in growing plants, they don’t like it and they reflect it, which is why most plants look green to us. But yellow light is very, very useful. It’s not just a cheery color. Yellow light is the farmer’s friend, and when you have a way of producing it at night from sunlight harvested during the day, that’s interesting.