Bioluminescence brings light to the ocean depths, turns beaches into nocturnal wonderlands, and allows fireflies to brighten our nights, but plants never mastered the art of bringing light into the world on their own. The transfer of bioluminescent firefly genes into plants was an early demonstration of transgenic technologies, but a new announcement promises to far exceed those short-lived glows.
Bacterial bioluminescent genes products proved toxic when introduced to plants, and firefly light didn't last long. Now Nature Biotechnology reports tobacco plants modified to incorporate genes from bioluminescent mushrooms have similar health measures and seed production to their wild counterparts, other than growing 12 percent taller, and the glow lasts the plants' whole lives.
“Thirty years ago, I helped to create the first luminescent plant using a gene from fireflies,” said Dr Keith Wood in a statement. “These new plants can produce a much brighter and more steady glow, which is fully embodied within their genetic code." The appropriately named Wood is CEO of Light Bio, a company planning to sell ornamental house plants that will allow you to find your way in the dark.
Sales to members of the public who want to make their houses look like the forests in Avatar may represent the commercial driver for the idea, but there are scientific benefits as well. The fluorescent jellyfish protein's discovery won a Nobel Prize for allowing scientists to identify which genes are activated at a particular time. A brighter and lasting glow could take botanists even further, allowing them to observe plant activity in previously impossible ways, including an instant healthcheck. The authors found plants glow most brightly when growing rapidly, and light output increases in the presence of ethylene – such as is produced by ripe banana skins – which encourages fruit to ripen.
The team responsible do not expect cities to replace streetlights with bioluminescent trees, as other teams have hoped. Not only is the light unlikely to ever be bright enough for that, but what is produced would spread in all directions, particularly up, greatly increasing light pollution compared to lights focussed downwards, and hindering our capacity to see the stars. Nightclubs, on the other hand, may love the indoor decor.
If all that was required to make plants glow like the brightest mushrooms was to move a single gene, the achievement would have been unlocked decades ago. Instead, the researchers had to understand the complex genetics that allows some fungi to convert caffeic acid into a precursor molecule, which releases light when it is oxidized, before being converted back to caffeic acid. The cycle requires the involvement of four different enzymes, the genes for each of which need to be transferred.
Plants use caffeic acid to make lignin, which gives cell walls their strength, so once the enzymes are there they have an abundance of material to work on.
Tobacco plants were chosen because their genetics are well understood (not through any desire to make glow-in-the-dark cigarettes). Having demonstrated success in that area the authors advanced to more marketable plants, with roses and petunia flowers producing particularly bright glows.
That may not be the end of the team's ambitions, however. The paper notes animals do not have caffeic acid, but additional enzymes could make it out of common molecules. Glowing pets, anyone?