What is it about?

Plants proliferate by a life cycle that involves sexual reproduction, in which flowering, fertilization, producing seeds creates genetic diversity within a population of the same species. Although sexual reproduction is also found in some unicellular algae, the ancestors of plants, sexual reproduction has never been found in many eukaryotic unicellular algae that emerged early in evolution. These unicellular algae have been believed to proliferate only by cell division (asexual reproduction). We show that one group of such organisms, unicellular red algae Galdieria spp., which inhabit sulfuric hot springs worldwide and have great potential for industrial use, undergo sexual reproduction. In addition, we have developed tools for genetic manipulation of these algae for elucidating algal and plant evolution and advancing microalgal industrial use.

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Why is it important?

The finding of sexual reproduction in the unicellular red algae provides information on the missing link of life cycle evolution in plant and algae. Besides its evolutionary importance, Galderia is expected to be used as new industrial microalgae. Galdieria shows remarkable metabolic capabilities, growing by photosynthesis, utilizing extracellular organic compounds, or both. Galdieria grows to a very high density (~100 g dried algae/L) and is rich in proteins and vitamins. Its acidic culture conditions reduce the risk of contamination by undesirable microorganisms. At this point, Galdieria is being developed for wastewater treatment, production of food ingredients and pigments. However, the known form of Galdieria cell (shown to be diploid phase by our study) is surrounded by a thick and rigid cell wall, requiring energy-intensive physical processing to extract the cellular contents and preventing the introduction of exogenous DNA and, thus, genetic modification. By finding cell wall-less haploid cells and cultivating them by asexual reproduction, we have succeeded in genetically manipulating Galdieiria. In addition, the newly found cell wall-less haploid makes cell disruption less cost intensive for industrial use of Galdieria.


Galdieria is also polyextremophile, tolerating very low pH (e.g. pH 0.1), higher salt and heavy metal concentrations than the other algae. Despite the versatility, genome size of Galdieria is very small among eukaryotic algae. The procedure for controlling the sexual life cycle, the genomic information, the genetic modification tools developed here provide a useful platform for understanding evolution of algae and plants, photosynthesis, metabolisms, and environmental adaptation in basic biology. The information and tools also facilitate industrial use of Galdieria and is expected to create advanced forms of microalgae utilization, such as vaccine-containing feed using algae expressing viral proteins as antigens.

Shin-ya Miyagishima
National Institute of Genetics

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This page is a summary of: Life cycle and functional genomics of the unicellular red alga Galdieria for elucidating algal and plant evolution and industrial use, Proceedings of the National Academy of Sciences, October 2022, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2210665119.
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