Presentation Information
[P04-549]Genomic and transcriptomic analysis of environmental stress adaptation in the oleaginous microalga Marinichlorella sp. NKG400014
○Ryota Kumakubo1, Kosuke Kataoka1,2, Tsuyoshi Tanaka1 (1. Graduate School of Engineering, Tokyo University of Agriculture and Technology (Japan), 2. Comprehensive Research Organization, Waseda University (Japan))
Keywords:
Marine green microalga,Stress tolerance,Comparative genomics,Transcriptome analysis,Lipid metabolism
[Purpose] Microalgae have gathered increasing attention for sustainable biofuel production. However, biomass productivity in large-scale outdoor cultivation systems is often reduced. The primary cause of this decline is environmental stress, particularly fluctuations in light intensity, temperature, and salinity. The marine green microalga genus Marinichlorella exhibits high environmental adaptability and lipid accumulation capacity, making it a promising industrial candidate. Nevertheless, genomic information remains limited, and the molecular basis underlying its stress tolerance has not been fully elucidated. This study aimed to elucidate the environmental stress response and tolerance mechanisms of Marinichlorella sp. NKG400014 through integrated comparative genomics and transcriptomic analyses.
[Method] A high-quality genome of Marinichlorella sp. NKG400014 was assembled using PacBio HiFi sequencing, followed by structural and functional annotations. For comparative genomics, 20 green algal genomes were analyzed to evaluate genome-scale phylogeny, gene family evolution, and lineage-specific functional signatures. Furthermore, RNA-seq analysis under nitrogen-depletion stress was conducted to investigate the transcriptional dynamics of stress- and lipid metabolism-related genes.
[Results&Consideration] The genome of Marinichlorella sp. NKG400014 was assembled into a 53.4 Mb genome with a GC content of 55.95%, comprising 10,326 predicted protein-coding genes. Both genome size and total gene number are comparable to those of closely related species, indicating no evidence of large-scale genome expansion. Gene family expansion analysis demonstrated enrichment of genes associated with light response, metal ion transport, and osmotic stress sensing, which are likely critical for adaptation to fluctuating marine environments. Such quantitative reinforcement of stress-related pathways likely contributes to improved tolerance to osmotic and high-light stresses in Marinichlorella sp. NKG400014.Furthermore, gene families related to lipid accumulation and carbohydrate metabolism were expanded in the common ancestor of Marinichlorella and Parachlorella, indicating evolutionary reinforcement of metabolic flexibility. Notably, genes involved in the pyruvate dehydrogenase (PDH) bypass pathway were expanded and transcriptionally induced under nitrogen-depletion stress. Because the canonical PDH complex is often sensitive to oxidative stress, the PDH bypass may enable sustained acetyl-CoA supply under stress conditions.
[Conclusion] This study provides integrated genomic and transcriptomic insights into the stress adaptation mechanisms of Marinichlorella sp. NKG400014. The identified gene family expansions and stress-inducible metabolic pathways, particularly the PDH bypass, highlight a potential adaptive metabolic strategy that supports stable lipid production under fluctuating marine conditions.
[Method] A high-quality genome of Marinichlorella sp. NKG400014 was assembled using PacBio HiFi sequencing, followed by structural and functional annotations. For comparative genomics, 20 green algal genomes were analyzed to evaluate genome-scale phylogeny, gene family evolution, and lineage-specific functional signatures. Furthermore, RNA-seq analysis under nitrogen-depletion stress was conducted to investigate the transcriptional dynamics of stress- and lipid metabolism-related genes.
[Results&Consideration] The genome of Marinichlorella sp. NKG400014 was assembled into a 53.4 Mb genome with a GC content of 55.95%, comprising 10,326 predicted protein-coding genes. Both genome size and total gene number are comparable to those of closely related species, indicating no evidence of large-scale genome expansion. Gene family expansion analysis demonstrated enrichment of genes associated with light response, metal ion transport, and osmotic stress sensing, which are likely critical for adaptation to fluctuating marine environments. Such quantitative reinforcement of stress-related pathways likely contributes to improved tolerance to osmotic and high-light stresses in Marinichlorella sp. NKG400014.Furthermore, gene families related to lipid accumulation and carbohydrate metabolism were expanded in the common ancestor of Marinichlorella and Parachlorella, indicating evolutionary reinforcement of metabolic flexibility. Notably, genes involved in the pyruvate dehydrogenase (PDH) bypass pathway were expanded and transcriptionally induced under nitrogen-depletion stress. Because the canonical PDH complex is often sensitive to oxidative stress, the PDH bypass may enable sustained acetyl-CoA supply under stress conditions.
[Conclusion] This study provides integrated genomic and transcriptomic insights into the stress adaptation mechanisms of Marinichlorella sp. NKG400014. The identified gene family expansions and stress-inducible metabolic pathways, particularly the PDH bypass, highlight a potential adaptive metabolic strategy that supports stable lipid production under fluctuating marine conditions.
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