Unraveling Vitamin B12-Responsive Gene Regulation in Algae
Unraveling Vitamin B12-Responsive Gene Regulation in Algae
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DOI：
10.1104/pp.113.234369
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发表时间：
2014-05-01
期刊：
影响因子：
7.4
通讯作者：
Smith, Alison G.
中科院分区：
文献类型：
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作者：
Helliwell, Katherine E.;Scaife, Mark A.;Smith, Alison G.
光合微藻在全球海洋和淡水系统的初级生产力和生物地球化学循环中发挥着至关重要的作用。然而，这些大都会生物的生长取决于维生素等营养物质的生物利用度。大约一半的微藻物种需要维生素 B-12 作为生长补充剂。藻类 B-12 需求的主要决定因素是藻类所拥有的蛋氨酸合酶同工型，因此，不依赖 B-12 的蛋氨酸合酶 (METE) 的存在使得藻类在没有这种维生素的情况下也能生长。此外，B-12 营养缺陷型在整个藻类谱系中广泛但与系统发育无关的分布表明 METE 基因在进化过程中多次丢失。鉴于 B-12 的存在会抑制 METE 表达，因此可靠的维生素来源的长期抑制可能会导致突变的积累，并最终导致基因丢失。在这里，我们探讨了海洋和淡水微藻物种中 B-12 和蛋氨酸/叶酸循环代谢物对 METE 基因的调控。此外，我们使用报告基因方法鉴定了莱茵衣藻 METE 的 B-12 响应元件。我们表明，报告基因的完全抑制是通过 METE 起始密码子上游 2574 至 290 bp 的区域发生的。蛋白质组学研究表明，莱茵衣藻中参与蛋氨酸-叶酸循环的另外两个基因（S-腺苷高半胱氨酸水解酶和丝氨酸羟甲基转移酶2）也受到 B-12 的抑制。 B-12 响应元件的强抑制性质和高灵敏度作为一种经济高效的调控基因表达工具，具有广阔的生物技术应用前景。
Photosynthetic microalgae play a vital role in primary productivity and biogeochemical cycling in both marine and freshwater systems across the globe. However, the growth of these cosmopolitan organisms depends on the bioavailability of nutrients such as vitamins. Approximately one-half of all microalgal species requires vitamin B-12 as a growth supplement. The major determinant of algal B-12 requirements is defined by the isoform of methionine synthase possessed by an alga, such that the presence of the B-12-independent methionine synthase (METE) enables growth without this vitamin. Moreover, the widespread but phylogenetically unrelated distribution of B-12 auxotrophy across the algal lineages suggests that the METE gene has been lost multiple times in evolution. Given that METE expression is repressed by the presence of B-12, prolonged repression by a reliable source of the vitamin could lead to the accumulation of mutations and eventually gene loss. Here, we probe METE gene regulation by B-12 and methionine/folate cycle metabolites in both marine and freshwater microalgal species. In addition, we identify a B-12-responsive element of Chlamydomonas reinhardtii METE using a reporter gene approach. We show that complete repression of the reporter occurs via a region spanning 2574 to 290 bp upstream of the METE start codon. A proteomics study reveals that two other genes (S-Adenosylhomocysteine hydrolase and Serine hydroxymethyltransferase2) involved in the methionine-folate cycle are also repressed by B-12 in C. reinhardtii. The strong repressible nature and high sensitivity of the B-12-responsive element has promising biotechnological applications as a cost-effective regulatory gene expression tool.