College of Food Science and Bioengineering, South China University of Technology, Guangzhou, China.
Department of Bioengineering, Imperial College London, London, UK.
Physiol Plant. 2024 Mar-Apr;176(2):e14296. doi: 10.1111/ppl.14296.
In Dunaliella tertiolecta, a microalga renowned for its extraordinary tolerance to high salinity levels up to 4.5 M NaCl, the mechanisms underlying its stress response have largely remained a mystery. In a groundbreaking discovery, this study identifies a choline dehydrogenase enzyme, termed DtCHDH, capable of converting choline to betaine aldehyde. Remarkably, this is the first identification of such an enzyme not just in D. tertiolecta but across the entire Chlorophyta. A 3D model of DtCHDH was constructed, and molecular docking with choline was performed, revealing a potential binding site for the substrate. The enzyme was heterologously expressed in E. coli Rosetta (DE3) and subsequently purified, achieving enzyme activity of 672.2 U/mg. To elucidate the role of DtCHDH in the salt tolerance of D. tertiolecta, RNAi was employed to knock down DtCHDH gene expression. The results indicated that the Ri-12 strain exhibited compromised growth under both high and low salt conditions, along with consistent levels of DtCHDH gene expression and betaine content. Additionally, fatty acid analysis indicated that DtCHDH might also be a FAPs enzyme, catalyzing reactions with decarboxylase activity. This study not only illuminates the role of choline metabolism in D. tertiolecta's adaptation to high salinity but also identifies a novel target for enhancing the NaCl tolerance of microalgae in biotechnological applications.
在杜氏盐藻中，一种以能耐受高达 4.5M NaCl 的高盐度而闻名的微藻，其应激反应的机制在很大程度上仍是一个谜。在一项开创性的发现中，本研究鉴定出一种胆碱脱氢酶，称为 DtCHDH，它能够将胆碱转化为甜菜碱醛。值得注意的是，这不仅是在杜氏盐藻中，而且是在整个绿藻门中首次鉴定出这种酶。构建了 DtCHDH 的 3D 模型，并进行了与胆碱的分子对接，揭示了一个潜在的底物结合位点。该酶在大肠杆菌 Rosetta（DE3）中异源表达，并随后进行纯化，实现了 672.2U/mg 的酶活。为了阐明 DtCHDH 在杜氏盐藻耐盐性中的作用，采用 RNAi 敲低 DtCHDH 基因表达。结果表明，Ri-12 株在高盐和低盐条件下的生长都受到了损害，同时 DtCHDH 基因表达和甜菜碱含量保持一致。此外，脂肪酸分析表明，DtCHDH 可能也是一种 FAPs 酶，具有脱羧酶活性的催化反应。本研究不仅阐明了胆碱代谢在杜氏盐藻适应高盐度中的作用，而且为增强生物技术应用中微藻对 NaCl 的耐受性提供了一个新的靶标。
