Research Centre for Environmental Bioscience, Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan.
Proc Natl Acad Sci U S A. 2013 Jan 29;110(5):1767-72. doi: 10.1073/pnas.1216234110. Epub 2013 Jan 7.
Photosynthesis in marine diatoms is a vital fraction of global primary production empowered by CO(2)-concentrating mechanisms. Acquisition of HCO(3)(-) from seawater is a critical primary step of the CO(2)-concentrating mechanism, allowing marine photoautotrophic eukaryotes to overcome CO(2) limitation in alkaline high-salinity water. However, little is known about molecular mechanisms governing this process. Here, we show the importance of a plasma membrane-type HCO(3)(-) transporter for CO(2) acquisition in a marine diatom. Ten putative solute carrier (SLC) family HCO(3)(-) transporter genes were found in the genome of the marine pennate diatom Phaeodactylum tricornutum. Homologs also exist in marine centric species, Thalassiosira pseudonana, suggesting a general occurrence of SLC transporters in marine diatoms. Seven genes were found to encode putative mammalian-type SLC4 family transporters in P. tricornutum, and three of seven genes were specifically transcribed under low CO(2) conditions. One of these gene products, PtSLC4-2, was localized at the plasmalemma and significantly stimulated both dissolved inorganic carbon (DIC) uptake and photosynthesis in P. tricornutum. DIC uptake by PtSLC4-2 was efficiently inhibited by an anion-exchanger inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, in a concentration-dependent manner and highly dependent on Na(+) ions at concentrations over 100 mM. These results show that DIC influx into marine diatoms is directly driven at the plasmalemma by a specific HCO(3)(-) transporter with a significant halophilic nature.
海洋硅藻的光合作用是全球初级生产力的重要组成部分，其由 CO2 浓缩机制提供动力。从海水中获取 HCO3-是 CO2 浓缩机制的关键初级步骤，使海洋光合真核生物能够克服碱性高盐水中的 CO2 限制。然而，对于控制这一过程的分子机制，人们知之甚少。在这里，我们展示了一种质膜型 HCO3-转运蛋白在海洋硅藻 CO2 摄取中的重要性。在海洋羽纹硅藻的基因组中发现了 10 个推测的溶质载体 (SLC) 家族 HCO3-转运蛋白基因。在海洋中心种塔玛亚历山大藻中也存在同源物，这表明 SLC 转运蛋白在海洋硅藻中普遍存在。在 P. tricornutum 中发现了 7 个基因编码推测的哺乳动物型 SLC4 家族转运蛋白，其中 7 个基因中有 3 个在低 CO2 条件下特异性转录。这些基因产物之一，PtSLC4-2，位于质膜上，可显著刺激 P. tricornutum 中溶解无机碳 (DIC) 的摄取和光合作用。PtSLC4-2 的 DIC 摄取可被阴离子交换抑制剂 4,4'-二异硫氰基二苯乙烯-2,2'-二磺酸以浓度依赖的方式有效抑制，且在超过 100 mM 的 Na+离子浓度下高度依赖。这些结果表明，DIC 流入海洋硅藻是由一种具有显著嗜盐性的特定 HCO3-转运蛋白在质膜上直接驱动的。
