Biologists uncover evidence of an evolutionary origin

Think of algae, and you might think of the shiny green threads looming in a stream or the bluish-green flowers that invade lakes. But the majority of these diverse aquatic organisms that exchange sunlight for energy are brown, like the large seagrass forests found in the polar or coastal regions of California.

Brown algae are brown (and therefore not pretty) because they have developed a special set of pigments that absorb more light for photosynthesis than green plants and green algae. This makes brown-colored algae so important to life on Earth, that it produces 20% of the oxygen we breathe. The biochemical mechanisms that make these brown algae so good at converting sunlight into energy have hitherto been a mystery to scientists.

Colorado State University biologists, in partnership with researchers in Germany and China, have unveiled fundamental new insights into the evolutionary steps taken by these algae to make new brown pigments called fucoxanthin.

Graham Beers, associate professor in CSU’s Department of Biology, co-led the study with Martin Loehr at Johannes Gutenberg-Universität in Germany and Xiaobo Li at Westlake University in Hangzhou, China. Posted in Proceedings of the National Academy of SciencesAnd the The team used a genetic screening method known as CRISPR/CAS9 to remove the function of the genes responsible for the algae’s brown pigment, turning its mutant varieties green in the process. CSU postdoctoral researcher Yu Bai was the first author of the manuscript.

Peers’ group, which studies the efficiency of photosynthesis and the ecophysiology of algae, identified the targets of the gene and performed experiments that allowed the team to see what happened when these brown pigment-related genes were inactivated.

Fucoxanthin has pharmaceutical and food applications

During the past decade, fucoxanthin has become the subject of increasing interest in food and pharmaceutical applications. The chemical structure of fucoxanthin was first mentioned in the scientific literature 150 years ago in the 1960s. What was not known was exactly how the algae manufactured this natural product.

This biochemical synthesis pathway was shown to be complex; Writing PNAS, The researchers showed that the brown pigment fucoxanthin evolved by duplicating ancient genes that generate light-protective pigments. Along the way, some of these gene copies acquired more and more complex functions, allowing the synthesis of other pigments that became highly suitable for photosynthesis.

“These algae are somehow able to mix and match, and then reprogram their cellular machinery to capture light in a way that land plants have not,” Beers said.

The new study provides a rich context in which to build further studies that could enable the transfer of the intense light-harvesting efficiency of brown pigment to other objects or uses.

For example, learning about how brown algae evolved could give scientists better insights into fucoxanthin as a nutrient for various health applications. And in biofuels research, understanding how to change the content of this pigment in a cell could better harness the efficiency of photosynthesis to produce more biofuels with the same amount of light, earth, and effort as conventional fuels.

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