Would you like to have a pot of this plant that glows at night?

Editor: He Jian

The movie "Avatar" once showed such a magical world: at night on the planet Pandora, the city was full of self-luminous plants, as if dotting the starry sky in the darkness, giving people a dreamlike sense of mystery. Imagine how wonderful it would be to plant a large number of such luminous plants in our living environment! So, do such self-luminous plants also exist on Earth?

In fact, bioluminescence is quite common in nature. Currently, there are about 30 independent bioluminescent systems known, including bacteria, algae, fungi and invertebrates, and there are even fewer plants that can emit light. Liu Hongtao, a researcher at the Institute of Plant Physiology and Ecology of the Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, said that my country's lantern tree, Africa's night-light tree, and some aloes, dinoflagellates, and street lamp grasses in Africa are all luminous plants. Although the phenomenon of plants emitting light seems to be counterintuitive, it does exist and is not a hypothetical proposition.

At this point, some people may wonder: Aren't there "luminous mushrooms"? Dozens of species have been discovered. You should know that mushrooms are not plants, but fungi.

Why do some plants glow?

Take some aloe vera in Africa as an example. The main reason is that the leaves of these plants contain a lot of phosphorus, which can release a small amount of phosphine gas. Since phosphine has a very low ignition point, it can spontaneously combust in the air, so it will emit a light blue light. But at present, the purpose of plant luminescence is still unknown.

However, although mushrooms are not plants, the luminescence of mushrooms is mainly concentrated on an organic molecule that is also necessary for plants to make cell walls. It is caffeic acid, which can produce light through a metabolic cycle of four enzymes. Two enzymes convert caffeic acid into a luminescent precursor, which is then oxidized by a third enzyme to produce photons. The last enzyme converts the oxidized molecule back into caffeic acid, thus starting a new cycle.

In plants, caffeic acid is a component of lignin, which helps provide mechanical strength to cell walls. As such, it is part of plant lignocellulosic biomass, the most abundant renewable resource on Earth.

So some scientists began to imagine: Can we make plants glow through technological means? For example, transplanting genes from certain organisms into plants and making them work. Although the idea is good, it is by no means easy. It is not simply transferring luminous genes from one organism to another. Just like the gears inside a watch, the newly added genes must be able to function normally in the host. However, as a cheap and environmentally friendly light source, it still has a lot of support.

In fact, as early as the 1980s, scientists introduced firefly luciferase into plant cells or plants for expression. When the substrate luciferin and the energy substance adenosine triphosphate (ATP) were added through culture medium or watering, the plant tissues would emit firefly-like light. In addition, scientists have also obtained fluorescent plants by genetically engineering jellyfish fluorescent protein or improved fluorescent protein into plant tissues for expression in the laboratory. However, these luminous plants require exogenous substrates and energy, and have limitations such as weak luminescence, short duration, and difficulty in observation with the naked eye. Even the brightness effect of "reading at night with fireflies" cannot be achieved, and they are not truly self-luminous plants.

The experience gained from fireflies and jellyfish cannot be fully applied to plants, so scientists began to learn from luminous fungi, and this time they succeeded.

In 2020, in a latest achievement published in Nature Biotechnology, a team of 27 scientists, led by synthetic biologists Karen Sarkisyan and Dr. Ilia Yampolsky, used genetic technology to create plants that can continuously emit visible light.

Image from Xinhuanet

The researchers say the new technology has practical value and can be used for aesthetic purposes, most importantly creating glowing flowers and other ornamental plants. While replacing streetlights with trees that glow on their own is a bit too whimsical, the green fluorescence these plants emit from their life is truly pleasing.

Image from Xinhuanet

Each generation is brighter than the previous one

Here comes the creature that can realize lighting!

In May 2023, Du Hao's team at Zhejiang University further improved the system on this basis. In their research, they found that the content of caffeic acid, the biosynthetic precursor of luciferin, and the intermediate product galactose is the limiting factor for the luminescence intensity of plants. Through identification and screening, the research team obtained two catalytic enzyme genes from Brassica napus and Aspergillus nidulans, respectively.

By introducing these two genes into the FBP system, the catalytic enzymes produced by them can efficiently promote the synthesis and accumulation of large amounts of caffeic acid and lactobacillus in the plant body, thereby significantly increasing the content of luciferin, thereby successfully enhancing the luminescence intensity of the self-luminous plants.

This plant self-luminous system optimized by metabolic engineering has a brightness five times higher than the original one, and can continuously and stably emit light visible to the human eye. Even detached leaves can continue to glow for three days. When multiple flowering plants are placed together, the light they emit can illuminate a dark environment, and the brightness is enough for people to clearly see nearby large fonts. In the future, these plants will no longer be limited to laboratory research and testing purposes, but are also expected to be used in environmental lighting and other fields.

Do you think this is the limit? There are even better ones! Recently, the research team of Hefei Shenbi Biotechnology Co., Ltd. successfully developed China's first gene-edited high-brightness night self-luminous plant. Li Renhan, the head of the research team, said that the research team went through 532 technical iterations and overcame multiple technical difficulties. The most difficult one was how to make the plant glow to the point where it was visible to the naked eye. The team also successfully achieved high-throughput expression of exogenous genes in plant cells, breaking the barriers to gene expression. In addition, the research team also optimized the enzymes in the reaction process to improve the efficiency of the enzymes, while superimposing multiple genes and changing some restrictive genes of the plant itself, ultimately allowing the plant to reach a high-brightness state visible to the naked eye.

It is reported that compared with similar international products, Shenbi Bio's luminous plants have obvious advantages in brightness. These plants do not require long-term camera exposure, and the luminous effect can be quickly seen by the naked eye in a dark environment, which can achieve commercial lighting. At present, Shenbi Bio has successfully achieved high-brightness self-luminescence on a variety of plants including sunflowers, and has also expanded the luminous technology of other flower varieties, including the transformation of roses, roses, lilies and other flowers.

In the future, these luminous plants are expected to be used in the garden field, and even to create a real "Avatar" theme park.

Reference sources: Science Popularization China, Xinhuanet, Science and Technology Daily, etc.