Scientists have discovered a process of sexual reproduction in microalgae that helps them better understand algae and plant evolution. By Shunsuke Hirooka and Shin-ya Miyagishima, National Institute of Genetics, ROIS

Scientists have discovered a process of sexual reproduction in microalgae that helps them better understand algae and plant evolution. Their discovery could lead to new industrial applications for microalgae, ranging from wastewater treatment to the production of food ingredients and pigments.

A Japanese research team published their findings in Proceedings of the National Academy of Sciences week of October 3, 2022

The team conducted their research on Galdieria, a single-celled species of red microalgae found in the sulfuric acid hot springs worldwide and is expected to become an important source of human nutrition. Microalgae have a high ability to fix carbon dioxide. This fixation is the process by which carbon dioxide is converted into organic compounds. The fixation capacity of microalgae is higher than that of plants, and microalgae contain higher concentrations of proteins, vitamins, and pigments. In recent years, researchers and businesses have worked to develop the fast-growing Galdieria as an industrial source of vitamins and pigments.

Galdieria is quite versatile, able to produce its own energy through photosynthesis, using light and carbon dioxide. It uses a mixture of different energy and carbon sources and obtains its nutrients by consuming extracellular sugars or sugar alcohols. Galdieria can also tolerate higher levels of salt and heavy metals than many other microalgae. However, the genome size of Galdieria is very small.

Because of the versatility of Galdieria, scientists consider it a new system for the application of biotechnology. However, that’s why Galdieria is surrounded by thick and tough cell wall, it requires energy-intensive physical processing to extract its cellular contents. The cell wall also prevents genetic modification of Galdieria.

During the research, the team learned that the known form of Galdieria with a cell wall is diploid, a type of cell that contains two complete sets of chromosomes. However, when these diploids are exposed to a specific environment, a haploid without a cell wall is formed, and a haploid without a cell wall contains only one set of chromosomes.

For further research, the team was able to stably propagate a haploid without a cell wall and turn the haploid back into a diploid. “Thus, we have discovered a process of sexual reproduction in microalgae that appeared in the early stages of the evolution of algae and plants,” said Shunsuke Hiruka, a project associate professor at the National Institute of Genetics in Japan.

“We have successfully developed a technique for genetic modification of Galderia using cell wall-less haploids. The procedure allows the creation of “self-cloning” lines that do not contain any heterologous DNA sequence for industrial use. For example, we were able to create a blue algae (blue is the color of phycocyanin, which is used as a natural blue dye in some foods) that does not exist in nature,” said Shin-ya Miyagishima, a professor at Japan’s National Institute of Genetics.

The team’s findings are important because although sexual reproduction also occurs in some unicellular algae, the ancestors of plants, sexual reproduction was never found in many unicellular algae that appeared early in evolution. “These unicellular algae are thought to reproduce only cell divisionor asexual reproductionand the origin and evolutionary process of sexual reproduction in algae and plants were unclear,” Hiruka said.

Looking ahead, the researchers believe their findings will help further elucidate the evolutionary process and origins sexual reproduction in algae and plants. The team’s discoveries hold the potential to reveal exciting future uses for Galdieria microalgae.

“The haploid identified in this study has the same growth potential as the diploid, and its contents can be easily extracted and genetically modified, facilitating industrial useGaldieria and is expected to create advanced forms microalgae disposal, such as the use of feed containing the vaccine algae which express viral proteins as antigens,” Miyagishima said.

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Additional information:
Hirooka, Shunsuke et al., Life Cycle and Functional Genomics of the Unicellular Red Alga Galdieria for Elucidation of Algal and Plant Evolution and Industrial Use, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2210665119.

Courtesy of the Information and Systems Research Organization

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