University of the Ryukyus · Tropical Biosphere Research Center · 教授

Research keywordstropical plant biochemistry・isoprene biosynthesis・mimosine metabolism・brown algae polysaccharides・functional food resources

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• Fractionation and characterization of cell wall polysaccharides from the brown alga Cladosiphon okamuranus.2023 · Awanthi MGG, Umosa M, Yuguchi Y, Oku H, Kitahara K, Ito M, Tanaka A, Konishi T
• Molecular characteristics of isoprene synthase and its control effects on isoprene emissions from tropical trees.2023 · Oku H, Mutanda I, Inafuku M
• Isolation and characterization of mimosine degrading enzyme from Arthrobacter sp. Ryudai-S1.2022 · Leucaena leucocephala growing in the tropics and subtropics serves as potential forage for livestock because its foliage is rich in protein, fiber, and minerals. However, its use for livestock feed has been hindered by toxic nonprotein amino acid mimosine. Therefore, it is necessary to develop a method to reduce or eliminate mimosine from foliage. A previous study found that the fermentation of L. leucocephala foliage reduced the mimosine content and prompted the authors to isolate potent mimosine degrading microorganisms and characterize the mimosinase for the complete elimination of mimosine in the L. leucocephala foliage. The soil screening of the L. leucocephala tree surroundings led to the isolation of Arthrobacter sp. Ryudai-S1, which can degrade and assimilate mimosine as a nitrogen and carbon source. Mimosinase in this strain was found to be thermostable and showed strong activity. Docking model's inspection and the interaction energy calculation between mimosine-pyridoxal-5'-phosphate (PLP) complex and the active site of this enzyme identified 11 important amino acid residues that stabilized the binding. Of these amino acid residues, mutation experiment suggested that Tyr-263' and Phe-34 stabilizes the substrate binding and play a critical role in guiding the substrate to proper positions to accomplish high catalytic efficacy and selectivity. These observations suggest that Arthrobacter sp. Ryudai-S1 could be potentially useful for the development of L. leucocephala feed with reduced mimosine content.
• Plant hormone profile and control over isoprene biosynthesis in a tropical tree Ficus septica.2022 · Plant hormone signalling and the circadian clock have been implicated in the transcriptional control of isoprene biosynthesis. To gain more insight into the hormonal control of isoprene biosynthesis, the present study measured plant hormone concentrations in jasmonic acid (JA)-treated leaves of our previous model study, examined their relationship with gene expression of isoprene synthase (IspS) and hormone signalling transcription factors. Of the plant hormones, IAA and JA-Ile and their related transcription factors (MYC2 and SAUR21) were significantly correlated with IspS gene expression. Concentrations of cytokinins, isopentenyladenine (iP), trans-zeatin riboside (tZR) and cis-zeatin riboside (cZR), were similarly significantly correlated with IspS expression. However, there was no significant correlation between their related transcription factor (ARR-B) and IspS expression. The circadian clock-related gene PRR7, but not the transcription factor LHY, was highly correlated with IspS expression. These results suggest that the hormonal balance between JA-Ile and IAA plays a central role in transcriptional regulation of IspS through the transcription factors MYC2 and SAUR21, the early auxin responsive genes. The putative cis-acting elements for SAUR on the IspS promoter (TGTCNN and CATATG), in addition to the G-box for MYC2, support the above proposal. These results provide insightful information on the core components of plant hormone-related regulation of IspS under coordination with the circadian clock genes.

• ヒト卵子形成および胚発生における卵胞液中・血中脂肪酸の影響2016 · ■■■
• イソプレン合成を指標とした熱帯樹木の温度センシング及びシグナリング系の解明2015 · 基盤研究(C)
• マングローブ植物の耐塩機構におけるＮＯシグナリングの役割解明2015 · ■■■

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