Bioluminescent Torch Passed from Glowing to Dim Fungi

Artificially glowing yeast cells in a test tube. [Sergei Shakhov]

A set of bioluminescence genes has been transferred from one eukaryote, a glowing fungus called Neonothopanus nambi, to another eukaryote, a non-glowing fungus called Pichia pastoris. This relay race is no mere sport, and it concerns organisms other than yeast. Higher organisms including plants and animals are more likely to accept a bioluminescence pathway from another eukaryote than one from a bacterium. Moreover, if higher organisms are set aglow by genetic manipulation, they could push diverse biomedical and bioengineering applications across the finish line, including the much-discussed idea of replacing streetlights with glowing plants.

The eukaryote-friendly bioluminescence genes were identified and passed from glowing to non-glowing yeasts by an international team of scientists led by Ilia V. Yampolsky, a researcher at the Institute of Bioorganic Chemistry of the Russian Academy of Sciences in Moscow. Using library screening and genome analysis, the team identified the enzymes that contribute to the synthesis of luciferin. The scientists showed that fungal luciferin, the substrate for the bioluminescence reaction, is only two enzymatic steps away from a well-known metabolite, called caffeic acid, which the fungus generates.

Additional findings appeared November 26 in the Proceedings of the National Academy of Sciences, in an article titled, “Genetically encodable bioluminescent system from fungi.” The article emphasized that the expression of genes from the fungal bioluminescent pathway is not toxic to eukaryotic cells, and the luciferase can be easily co-opted to bioimaging applications.

“Here, we report identification of the fungal luciferase and three other key enzymes that together form the biosynthetic cycle of the fungal luciferin from caffeic acid, a simple and widespread metabolite,” the article’s authors wrote. “Introduction of the identified genes into the genome of the yeast Pichia pastoris along with caffeic acid biosynthesis genes resulted in a strain that is autoluminescent in standard media.”

Comparing mushrooms that glow with those that don’t, co-author Fyodor Kondrashov, Ph.D., professor at the Institute of Science and Technology Austria (IST Austria) and colleagues also uncovered how gene duplication allowed bioluminescence to evolve more than a hundred million years ago. Why it evolved is still unclear.

The fungus Neonothopanus nambi. [Cassius V. Stevani]
So, is bioluminescence beneficial or just a side product? “We don’t know yet,” said Dr. Kondrashov. “There are evidences that the glow attracts insects which distribute the spores. But I don’t think that’s convincing.”

Knowing how bioluminescent fungi glow, the researchers then lit up non-bioluminescent eukaryotes. Inserting the gene encoding luciferase in Neonothopanus nambi along with three other genes whose products form the chain that converts the metabolite caffeic acid into the substrate for the reaction, luciferin, into the yeast Pichia pastoris resulted in glowing colonies of yeasts. “We don’t supply a chemical that makes the yeast glow. Instead, we supply the enzymes it needs to convert a metabolic product that is already present in the yeast into light,” explained Dr. Kondrashov.

This discovery could find widespread applications, from tissues that report changes in their physiology by lighting up to creating glowing animals and plants. “If we think of sci-fi scenarios in which glowing plants replace street lights—this is it. This is the breakthrough that can lead to this,” Dr. Kondrashov declared. “However, it may take several years until such a plant street light is engineered.”

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