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内容記述 |
Although microalgae such as diatoms and haptophytes have been studied to optimize fucoxanthin production, the complete biosynthetic pathway of fucoxanthin remains unclear. In this study, we subjected the haptophyte Tisochrysis lutea cells to heavy-ion beam irradiation to induce random mutations and obtained two greenish strains, GR1 and GR2, following exposures to 45 Gy and 100 Gy, respectively. The GR1 strain exhibited slow growth, whereas GR2 showed growth comparable to both the wild-type strain and the parental strain C8-14. Neither GR1 nor GR2 accumulated fucoxanthin; instead, both strains accumulated fucoxanthin biosynthetic intermediates, haptoxanthin and phaneroxanthin, and harbored 74 and 148 mutation sites, respectively. As expected, higher radiation doses resulted in a greater number of mutations. Over 80% of these mutations consisted of short nucleotide insertions, primarily 4 to 8 bp in length. Additionally, mutations were identified in orthologs of the ZEP1 and CRTISO5 genes known in the diatom Phaeodactylum tricornutum to encode enzymes that convert haptoxanthin to phaneroxanthin and phaneroxanthin into fucoxanthin, respectively, in both GR1 and GR2 strains. Because the genomic analysis results aligned with those from pigment analysis, our findings demonstrate that ZEP1 and CRTISO5 in T. lutea cells are involved in fucoxanthin biosynthesis and support the broader application of heavy-ion beam irradiation in fundamental microalgal research. |
