University of the Ryukyus · Graduate School of Science and Engineering · 准教授

Research keywordsunicellular red algae・Cyanidioschyzon merolae・trophic transitions・polyphosphate metabolism・mitochondrial division・eukaryotic evolution

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• A high-yield protein expression platform in the unicellular red alga Cyanidioschyzon merolae.2026 · The production of engineered proteins in transgenic cells is widely used in research, medicine and industry. However, conventional cell-based production systems still face challenges in cost, scalability and biosafety. Here, we present a recombinant protein expression platform with simplified purification based on the photosynthetic unicellular red alga Cyanidioschyzon merolae, which can be cultivated under highly acidic conditions using only inorganic nutrients, air, water and light. We first identified a promoter that drives high-level constitutive gene expression throughout the cell cycle, resulting in substantial mRNA accumulation in C. merolae. A stable transformant expressing His-tagged mVenus under the control of this promoter accumulated the recombinant protein to more than 1% of total soluble protein. The simple cellular architecture of C. merolae, including the absence of a cell wall, enables efficient protein extraction via a single freeze-thaw cycle, followed by purification using immobilized metal affinity chromatography (IMAC), yielding ∼13.9 mg of functional recombinant protein per gram of total soluble protein. Owing to its low cost, scalability, operational simplicity and minimal risk of contamination, this Cyanidioschyzon-based platform offers a practical and promising approach to recombinant protein production in a photosynthetic eukaryote.
• Sexual life cycle establishes the unicellular red algae Cyanidiophyceae as a genetically tractable model lineage for eukaryotic evolution2025 · Abstract The thermo-acidophilic unicellular algal class Cyanidiophyceae is the earliest-branching lineage in red algae, which diverged from Viridiplantae lineage (green algae and land plants) soon after chloroplast establishment in the common ancestor of Archaeplastida. Cyanidiophyceae possess extremely simple genomes (8.7–17.8 Mb; approximately 4,800– 7,800 genes), and the cell-wall-less, genetically tractable strain Cyanidioschyzon merolae 10D has served as a model organism. However, its unknown sexual life cycle has limited its utility in studies of evolution and genetics. Inspired by the recent discovery of sexual reproduction in the cyanidiophycean genus Galdieria, we identified similar life cycles in the other cyanidiophycean genera Cyanidioschyzon, Cyanidiococcus, and Cyanidium. In these genera, the cell-walled diploid form, exclusively observed in nature, produces a cell-wall-less haploid form when the culture pH is lowered, and both proliferate asexually. In addition, the cell-wall-less Cyanidioschyzon merolae 10D strain has been shown to be a haploid clone that forms a cell-walled diploid through mating with other haploid clones. Building on these findings, we generated high-quality genomic resources with phase-specific transcriptomes and developed genetic manipulation systems using the cell-wall-less haploids of these genera. We further uncovered phase-specific distribution of histone H3 lysine 27 trimethylation linked to haploid- and diploid-specific gene expression, including transcription factors involved in differentiation associated with sexual reproduction in plants. Additionally, biparental inheritance of organelle DNA occurs following isogamous mating of haploid cells but resolves into uniparental inheritance during diploid proliferation. These advances position Cyanidiophyceae as a powerful model lineage for studying early Archaeplastida evolution, the shared mechanisms of photosynthetic eukaryotes, and their environmental adaptation.
• Costs of photosynthesis and cellular remodeling in trophic transitions of the unicellular red alga Galdieria partita.2025 · Yamashita S, Hirooka S, Fujiwara T, Zhou B, Yagisawa F, Tamashiro K, Murakami H, Awai K, Miyagishima SY
• Heterotrophic unicellular eukaryotes feeding on the unicellular red alga Cyanidiococcus sp. in moderately hot geothermal sulfuric springs.2025 · Sulfuric acidic hot springs (<pH 4.0, >37°C) are found in volcanic regions worldwide, where various bacteria, archaea, and the unicellular red algae Cyanidiophyceae dominate. Regarding heterotrophic eukaryotes, the only known species was the thermophilic amoeboflagellate Tetramitus thermacidophilus (class Eutetramitea, phylum Heterolobosea), which feeds on surrounding bacteria and archaea. In this study, we investigated three sulfuric hot springs (34.7°C-50°C, ∼pH 2.0) in Japan to determine whether other heterotrophic eukaryotes inhabit these environments. As a result, we isolated and identified cultures of four species capable of surviving at pH 2.0 and 40°C: Allovahlkampfia sp. (Eutetramitea, Heterolobosea); Nuclearia sp. and Parvularia sp. (Nucleariidea, Cristidiscoidea); and Vannella sp. (Discosea, Amoebozoa). Phylogenetic analyses suggest that these four species independently evolved from mesophilic and neutrophilic ancestors, separate from each other. Additionally, Platyophrya sp. (Colpodea, Ciliophora) and two species of Neobodo (Euglenozoa, Kinetoplastea) were also found in the same environment, while their maximum survival temperatures were 35°C and 30°C, respectively. Among these, all species except Neobodo were confirmed to grow exclusively by feeding on Cyanidiococcus sp., a dominant species of Cyanidiophyceae in the environment. Thus, various lineages of heterotrophic unicellular eukaryotes have independently developed acidophilic and thermotolerant traits, allowing them to colonize sulfuric hot springs.

• 紅藻におけるMYB転写因子とポリリン酸代謝が介するリン酸飢餓応答機構の解明2025 · 基盤研究(C)
• 微細藻類のオルガネラ分裂機構を基盤に植物細胞の基を解く2022 · 基盤研究(B)
• 真核光合成生物における貯蔵物質代謝を介した生存戦略の解明2022 · 物は無機および有機養分の枯渇に備えてこれらを貯蔵し、必要時に利用する。このような貯蔵物質の合成と分解は、生物の持つ最も基本的な生存戦略の一つであるが、この戦略を支えるしくみはよく分かっていない。たとえば、貯蔵物質の合成と分解の切り替えは直近の代謝経路だけでなく、他の代謝経路群の変動も必要とすることが予想されるが、このような包括的な変動はほとんど議論されていない。本研究では、ゲノムサイズが小さく遺伝子組換え技術が確立された単細胞藻類をモデルに、貯蔵物質の合成・分解の切り替えに伴う細胞全体の代謝変動などを解析し、光合成生物における貯蔵物質代謝を介した生存戦略を明らかにする。
• オルガネラ分裂/増殖機構を基盤にした真核植物細胞の基のゲノム形態学的解明2019 · 真核生物に共通のオルガネラの増殖を考慮した細胞分裂の機構を、原始紅藻 C.merolae (シゾン）を基盤に調べた。各包膜オルガネラが分裂装置を使って順次分裂すること、更に各分裂装置の構成物質を確かめた。分裂したオルガネラの分配にTOP（キネシン様物質）が働き細胞核分裂を起こし、次に細胞膜の収縮物質(EF1α)が作動した。窪んだ中央細胞膜に収縮分子類（ESCRTIII, ALIX, VPS4等）が現れ分裂を促した。ESCRTIIIは「電子密度の高いリング」と複合体を形成し、最終分断を起こすと推定され、類似のリングはメダカモでも観察された。またシゾンにおいて中期染色体構造が確認された。

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