Thanks to a unique type of chlorophyll, marine algae thrive in aquatic environments. However, the pathways responsible for synthesizing this pigment have long remained a secret of the ocean. In a study led by Tingting Xiang, an assistant professor of bioengineering at UC Riverside, scientists sought a greater understanding of the genetic basis of this adaptation. With marine algae responsible for generating a substantial portion of the Earth's oxygen and sustaining vital marine ecosystems, this revelation is a major step towards comprehending and capturing these organisms' resilience.

"Marine algae produce half of all the oxygen we breathe, even more than plants on land. And they feed huge food webs, fish that get eaten by mammals and humans," remarked Tingting Xiang. "Despite their global significance, we did not understand the genetic basis for the algae’s survival, until now."

The study, published in Current Biology, also details the successful transfer of the gene responsible for chlorophyll c production into a terrestrial plant, a feat with profound biotechnological implications. Chlorophyll facilitates photosynthesis, the vital process of converting light into energy. The absorption spectrum of these pigments determines how much solar energy is captured and can be funneled into the process. “Chlorophylls b and c absorb light at different wavelengths,” Xiang explained. “The ocean absorbs red light, which is why it looks blue. Chlorophyll c evolved to capture the blue-green light penetrating deeper into the water.”

By making a fuller spectrum of light available to the modified plants, more energy is consequently available for growth. This feat opens the door to potentially enhancing crop yields while reducing the demand for arable land, offering a promising avenue for addressing food security challenges.

The implications extend beyond agricultural innovation, with potential applications in the realm of renewable energy. By leveraging this newfound understanding of chlorophyll biosynthesis, researchers envision optimizing algae for biofuel production, bolstering the viability of sustainable energy alternatives.

This groundbreaking discovery was something of a surprise to the researchers. The study began as an investigation into algae that reside in coral and share sugars with their hosts. Each coral colony has thousands of polyps, and their brown color is from the algae. Whenever you see coral bleaching, it’s due to the loss of the algae,” Xiang said.

In an attempt to understand how the photosynthetic capabilities of the algae might affect the coral, the researchers began to study mutant algae, characterized by their inability to perform photosynthesis. The researchers discovered that these mutants were surprisingly still able to survive, just on the sustenance provided by their coral hosts. By using next-generation DNA sequencing to investigate the genome of these unusual specimens, the researchers uncovered the gene responsible for chlorophyll c production. 

“Discovering the chlorophyll c gene was not the initial goal of our work. We made the mutants for another reason, but I guess we were just lucky,” Xiang stated.

As the scientific community grapples with mounting concerns over coral bleaching and climate change, the newfound understanding of chlorophyll biosynthesis harbors potential remedies. By harnessing this knowledge, researchers can seek mitigations to the adverse impacts of environmental stressors on coral reefs alongside exploring avenues for sustainable agricultural practices and renewable energy solutions.

"The identification of the biosynthetic pathway for chlorophyll c is more than a scientific curiosity; it's a potential game-changer for sustainable energy and food security," emphasized Robert Jinkerson, a chemical engineering professor at UCR and co-author of the study.

"By unlocking the secrets of this key pigment, we're not only gaining insights into the lifeblood of marine ecosystems but also pioneering a path towards developing more robust crops and efficient biofuels," Jinkerson concluded.

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